Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Dmitry Baryshkov]

On 25/02/2023 02:36, Abhinav Kumar wrote:
> 
> 
> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar 
>> <quic_abhinavk@quicinc.com> wrote:
>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar 
>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>> Add DSC helper functions based on DSC configuration profiles to 
>>>>>>> produce
>>>>>>> DSC related runtime parameters through both table look up and 
>>>>>>> runtime
>>>>>>> calculation to support DSC on DPU.
>>>>>>>
>>>>>>> There are 6 different DSC configuration profiles are supported 
>>>>>>> currently.
>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC 
>>>>>>> version (V1.1),
>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>
>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>
>>>>>> These helpers should go to drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>> Also please check that they can be used for i915 or for amdgpu 
>>>>>> (ideally for both of them).
>>>>>>
>>>>>
>>>>> No, it cannot. So each DSC encoder parameter is calculated based on 
>>>>> the HW core which is being used.
>>>>>
>>>>> They all get packed to the same DSC structure which is the struct 
>>>>> drm_dsc_config but the way the parameters are computed is specific 
>>>>> to the HW.
>>>>>
>>>>> This DPU file helper still uses the drm_dsc_helper's 
>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but the 
>>>>> parameters themselves are very HW specific and belong to each 
>>>>> vendor's dir.
>>>>>
>>>>> This is not unique to MSM.
>>>>>
>>>>> Lets take a few other examples:
>>>>>
>>>>> AMD: 
>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
>>>>>
>>>>> i915: 
>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
>>>>
>>>> I checked several values here. Intel driver defines more bpc/bpp 
>>>> combinations, but the ones which are defined in intel_vdsc and in 
>>>> this patch seem to match. If there are major differences there, 
>>>> please point me to the exact case.
>>>>
>>>> I remember that AMD driver might have different values.
>>>>
>>>
>>> Some values in the rc_params table do match. But the rc_buf_thresh[] 
>>> doesnt.
>>
>> Because later they do:
>>
>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>
>>>
>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
>>>
>>> Vs
>>>
>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>> +};
>>
>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>> standard. As it's done in the Intel driver.
>>
> 
> Got it, thanks
> 
>>> I dont know the AMD calculation very well to say that moving this to the
>>> helper is going to help.
>>
>> Those calculations correspond (more or less) at the first glance to
>> what intel does for their newer generations. I think that's not our
>> problem for now.
>>
> 
> Well, we have to figure out if each value matches and if each of them 
> come from the spec for us and i915 and from which section. So it is 
> unfortunately our problem.

Otherwise it will have to be handled by Marijn, me or anybody else 
wanting to hack up the DSC code. Or by anybody adding DSC support to the 
next platform and having to figure out the difference between i915, msm 
and their platform.

> 
>>>
>>> Also, i think its too risky to change other drivers to use whatever math
>>> we put in the drm_dsc_helper to compute thr RC params because their code
>>> might be computing and using this tables differently.
>>>
>>> Its too much ownership for MSM developers to move this to drm_dsc_helper
>>> and own that as it might cause breakage of basic DSC even if some values
>>> are repeated.
>>
>> It's time to stop thinking about ownership and start thinking about
>> shared code. We already have two instances of DSC tables. I don't
>> think having a third instance, which is a subset of an existing
>> dataset, would be beneficial to anybody.
>> AMD has complicated code which supports half-bit bpp and calculates
>> some of the parameters. But sharing data with the i915 driver is
>> straightforward.
>>
> 
> Sorry, but I would like to get an ack from i915 folks if this is going
> to be useful to them if we move this to helper because we have to look 
> at every table. Not just one.

Added i915 maintainers to the CC list for them to be able to answer.

> 
> Also, this is just 1.1, we will add more tables for 1.2. So we will have 
> to end up changing both 1.1 and 1.2 tables as they are different for QC.

I haven't heard back from Kuogee about the possible causes of using 
rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on 
that? In other words, can we always stick to the values from 1.2 
standard? What will be the drawback?

Otherwise, we'd have to have two different sets of values, like you do 
in your vendor driver.

> So if you look at the DSC spec from where these tables have come it says
> 
> "Common Recommended Rate Control-Related Parameter Values"
> 
> Its Recommended but its NOT mandated by the spec to follow every value 
> to the dot. I have confirmed this point with more folks.
> 
> So, if someone from i915 this is useful and safe to move their code to 
> the tables, we can try it.
> 
>>> I would prefer to keep it in the msm code but in a top level directory
>>> so that we dont have to make DSI dependent on DPU.
>>
>> I haven't changed my opinion. Please move relevant i915's code to
>> helpers, verify data against standards and reuse it.
>>
> 
> 
> 
>>>>> All vendors compute the values differently and eventually call 
>>>>> drm_dsc_compute_rc_parameters()
>>>>>
>>>>>> I didn't check the tables against the standard (or against the 
>>>>>> current source code), will do that later.
>>

-- 
With best wishes
Dmitry

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

Hi Dmitry

On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>
>>
>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar 
>>> <quic_abhinavk@quicinc.com> wrote:
>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar 
>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>> Add DSC helper functions based on DSC configuration profiles to 
>>>>>>>> produce
>>>>>>>> DSC related runtime parameters through both table look up and 
>>>>>>>> runtime
>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>
>>>>>>>> There are 6 different DSC configuration profiles are supported 
>>>>>>>> currently.
>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC 
>>>>>>>> version (V1.1),
>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>
>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>
>>>>>>> These helpers should go to drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>> Also please check that they can be used for i915 or for amdgpu 
>>>>>>> (ideally for both of them).
>>>>>>>
>>>>>>
>>>>>> No, it cannot. So each DSC encoder parameter is calculated based 
>>>>>> on the HW core which is being used.
>>>>>>
>>>>>> They all get packed to the same DSC structure which is the struct 
>>>>>> drm_dsc_config but the way the parameters are computed is specific 
>>>>>> to the HW.
>>>>>>
>>>>>> This DPU file helper still uses the drm_dsc_helper's 
>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but the 
>>>>>> parameters themselves are very HW specific and belong to each 
>>>>>> vendor's dir.
>>>>>>
>>>>>> This is not unique to MSM.
>>>>>>
>>>>>> Lets take a few other examples:
>>>>>>
>>>>>> AMD: 
>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165 
>>>>>>
>>>>>>
>>>>>> i915: 
>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379 
>>>>>>
>>>>>
>>>>> I checked several values here. Intel driver defines more bpc/bpp 
>>>>> combinations, but the ones which are defined in intel_vdsc and in 
>>>>> this patch seem to match. If there are major differences there, 
>>>>> please point me to the exact case.
>>>>>
>>>>> I remember that AMD driver might have different values.
>>>>>
>>>>
>>>> Some values in the rc_params table do match. But the rc_buf_thresh[] 
>>>> doesnt.
>>>
>>> Because later they do:
>>>
>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>
>>>>
>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40 
>>>>
>>>>
>>>> Vs
>>>>
>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>> +};
>>>
>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>> standard. As it's done in the Intel driver.
>>>
>>
>> Got it, thanks
>>
>>>> I dont know the AMD calculation very well to say that moving this to 
>>>> the
>>>> helper is going to help.
>>>
>>> Those calculations correspond (more or less) at the first glance to
>>> what intel does for their newer generations. I think that's not our
>>> problem for now.
>>>
>>
>> Well, we have to figure out if each value matches and if each of them 
>> come from the spec for us and i915 and from which section. So it is 
>> unfortunately our problem.
> 
> Otherwise it will have to be handled by Marijn, me or anybody else 
> wanting to hack up the DSC code. Or by anybody adding DSC support to the 
> next platform and having to figure out the difference between i915, msm 
> and their platform.
> 

Yes, I wonder why the same doubt didn't arise when the other vendors 
added their support both from other maintainers and others.

Which makes me think that like I wrote in my previous response, these 
are "recommended" values in the spec but its not mandatory.

Moving this to the drm_dsc_helper is generalizing the tables and not 
giving room for the vendors to customize even if they want to (which the 
spec does allow).

So if this has any merit and if you or Marijn would like to take it up, 
go for it. We would do the same thing as either of you would have to in 
terms of figuring out the difference between msm and the i915 code.

This is not a generic API we are trying to put in a helper, these are 
hard-coded tables so there is a difference between looking at these Vs 
looking at some common code which can move to the core.

>>
>>>>
>>>> Also, i think its too risky to change other drivers to use whatever 
>>>> math
>>>> we put in the drm_dsc_helper to compute thr RC params because their 
>>>> code
>>>> might be computing and using this tables differently.
>>>>
>>>> Its too much ownership for MSM developers to move this to 
>>>> drm_dsc_helper
>>>> and own that as it might cause breakage of basic DSC even if some 
>>>> values
>>>> are repeated.
>>>
>>> It's time to stop thinking about ownership and start thinking about
>>> shared code. We already have two instances of DSC tables. I don't
>>> think having a third instance, which is a subset of an existing
>>> dataset, would be beneficial to anybody.
>>> AMD has complicated code which supports half-bit bpp and calculates
>>> some of the parameters. But sharing data with the i915 driver is
>>> straightforward.
>>>
>>
>> Sorry, but I would like to get an ack from i915 folks if this is going
>> to be useful to them if we move this to helper because we have to look 
>> at every table. Not just one.
> 
> Added i915 maintainers to the CC list for them to be able to answer.
> 

Thanks, lets wait to hear from them about where finally these tables 
should go but thats can be taken up as a separate effort too.

>>
>> Also, this is just 1.1, we will add more tables for 1.2. So we will 
>> have to end up changing both 1.1 and 1.2 tables as they are different 
>> for QC.
> 
> I haven't heard back from Kuogee about the possible causes of using 
> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on 
> that? In other words, can we always stick to the values from 1.2 
> standard? What will be the drawback?
> 
> Otherwise, we'd have to have two different sets of values, like you do 
> in your vendor driver.
> 

I have responded to this in the other email.

All this being said, even if the rc tables move the drm_dsc_helper 
either now or later on, we will still need MSM specific calculations for 
many of the other encoder parameters (which are again either hard-coded 
or calculated). Please refer to the sde_dsc_populate_dsc_config() 
downstream. And yes, you will not find those in the DP spec directly.

So we will still need a dsc helper for MSM calculations to be common for 
DSI / DP irrespective of where the tables go.

So, lets finalize that first.

>> So if you look at the DSC spec from where these tables have come it says
>>
>> "Common Recommended Rate Control-Related Parameter Values"
>>
>> Its Recommended but its NOT mandated by the spec to follow every value 
>> to the dot. I have confirmed this point with more folks.
>>
>> So, if someone from i915 this is useful and safe to move their code to 
>> the tables, we can try it.
>>
>>>> I would prefer to keep it in the msm code but in a top level directory
>>>> so that we dont have to make DSI dependent on DPU.
>>>
>>> I haven't changed my opinion. Please move relevant i915's code to
>>> helpers, verify data against standards and reuse it.
>>>
>>
>>
>>
>>>>>> All vendors compute the values differently and eventually call 
>>>>>> drm_dsc_compute_rc_parameters()
>>>>>>
>>>>>>> I didn't check the tables against the standard (or against the 
>>>>>>> current source code), will do that later.
>>>
> 

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Dmitry Baryshkov]

On 26/02/2023 02:47, Abhinav Kumar wrote:
> Hi Dmitry
> 
> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>
>>>
>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar 
>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar 
>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>> Add DSC helper functions based on DSC configuration profiles to 
>>>>>>>>> produce
>>>>>>>>> DSC related runtime parameters through both table look up and 
>>>>>>>>> runtime
>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>
>>>>>>>>> There are 6 different DSC configuration profiles are supported 
>>>>>>>>> currently.
>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC 
>>>>>>>>> version (V1.1),
>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>
>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>
>>>>>>>> These helpers should go to drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>> Also please check that they can be used for i915 or for amdgpu 
>>>>>>>> (ideally for both of them).
>>>>>>>>
>>>>>>>
>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based 
>>>>>>> on the HW core which is being used.
>>>>>>>
>>>>>>> They all get packed to the same DSC structure which is the struct 
>>>>>>> drm_dsc_config but the way the parameters are computed is 
>>>>>>> specific to the HW.
>>>>>>>
>>>>>>> This DPU file helper still uses the drm_dsc_helper's 
>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but the 
>>>>>>> parameters themselves are very HW specific and belong to each 
>>>>>>> vendor's dir.
>>>>>>>
>>>>>>> This is not unique to MSM.
>>>>>>>
>>>>>>> Lets take a few other examples:
>>>>>>>
>>>>>>> AMD: 
>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
>>>>>>>
>>>>>>> i915: 
>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
>>>>>>
>>>>>> I checked several values here. Intel driver defines more bpc/bpp 
>>>>>> combinations, but the ones which are defined in intel_vdsc and in 
>>>>>> this patch seem to match. If there are major differences there, 
>>>>>> please point me to the exact case.
>>>>>>
>>>>>> I remember that AMD driver might have different values.
>>>>>>
>>>>>
>>>>> Some values in the rc_params table do match. But the 
>>>>> rc_buf_thresh[] doesnt.
>>>>
>>>> Because later they do:
>>>>
>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>
>>>>>
>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
>>>>>
>>>>> Vs
>>>>>
>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>> +};
>>>>
>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>>> standard. As it's done in the Intel driver.
>>>>
>>>
>>> Got it, thanks
>>>
>>>>> I dont know the AMD calculation very well to say that moving this 
>>>>> to the
>>>>> helper is going to help.
>>>>
>>>> Those calculations correspond (more or less) at the first glance to
>>>> what intel does for their newer generations. I think that's not our
>>>> problem for now.
>>>>
>>>
>>> Well, we have to figure out if each value matches and if each of them 
>>> come from the spec for us and i915 and from which section. So it is 
>>> unfortunately our problem.
>>
>> Otherwise it will have to be handled by Marijn, me or anybody else 
>> wanting to hack up the DSC code. Or by anybody adding DSC support to 
>> the next platform and having to figure out the difference between 
>> i915, msm and their platform.
>>
> 
> Yes, I wonder why the same doubt didn't arise when the other vendors 
> added their support both from other maintainers and others.
> 
> Which makes me think that like I wrote in my previous response, these 
> are "recommended" values in the spec but its not mandatory.

I think, it is because there were no other drivers to compare. In other 
words, for a first driver it is pretty logical to have everything 
handled on its own. As soon as we start getting other implementations of 
a feature, it becomes logical to think if the code can be generalized. 
This is what we see we with the HDCP series or with the code being moved 
to DP helpers.

> 
> Moving this to the drm_dsc_helper is generalizing the tables and not 
> giving room for the vendors to customize even if they want to (which the 
> spec does allow).

That depends on the API you select. For example, in 
intel_dsc_compute_params() I see customization being applied to 
rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.

In case the driver needs to perform customization of the params, nothing 
stops it drop applying after filling all the RC params in the 
drm_dsc_config struct via the generic helper.


> So if this has any merit and if you or Marijn would like to take it up, 
> go for it. We would do the same thing as either of you would have to in 
> terms of figuring out the difference between msm and the i915 code.
> 
> This is not a generic API we are trying to put in a helper, these are 
> hard-coded tables so there is a difference between looking at these Vs 
> looking at some common code which can move to the core.
> 
>>>
>>>>>
>>>>> Also, i think its too risky to change other drivers to use whatever 
>>>>> math
>>>>> we put in the drm_dsc_helper to compute thr RC params because their 
>>>>> code
>>>>> might be computing and using this tables differently.
>>>>>
>>>>> Its too much ownership for MSM developers to move this to 
>>>>> drm_dsc_helper
>>>>> and own that as it might cause breakage of basic DSC even if some 
>>>>> values
>>>>> are repeated.
>>>>
>>>> It's time to stop thinking about ownership and start thinking about
>>>> shared code. We already have two instances of DSC tables. I don't
>>>> think having a third instance, which is a subset of an existing
>>>> dataset, would be beneficial to anybody.
>>>> AMD has complicated code which supports half-bit bpp and calculates
>>>> some of the parameters. But sharing data with the i915 driver is
>>>> straightforward.
>>>>
>>>
>>> Sorry, but I would like to get an ack from i915 folks if this is going
>>> to be useful to them if we move this to helper because we have to 
>>> look at every table. Not just one.
>>
>> Added i915 maintainers to the CC list for them to be able to answer.
>>
> 
> Thanks, lets wait to hear from them about where finally these tables 
> should go but thats can be taken up as a separate effort too.
> 
>>>
>>> Also, this is just 1.1, we will add more tables for 1.2. So we will 
>>> have to end up changing both 1.1 and 1.2 tables as they are different 
>>> for QC.
>>
>> I haven't heard back from Kuogee about the possible causes of using 
>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on 
>> that? In other words, can we always stick to the values from 1.2 
>> standard? What will be the drawback?
>>
>> Otherwise, we'd have to have two different sets of values, like you do 
>> in your vendor driver.
>>
> 
> I have responded to this in the other email.
> 
> All this being said, even if the rc tables move the drm_dsc_helper 
> either now or later on, we will still need MSM specific calculations for 
> many of the other encoder parameters (which are again either hard-coded 
> or calculated). Please refer to the sde_dsc_populate_dsc_config() 
> downstream. And yes, you will not find those in the DP spec directly.
> 
> So we will still need a dsc helper for MSM calculations to be common for 
> DSI / DP irrespective of where the tables go.
> 
> So, lets finalize that first.

I went on and trimmed sde_dsc_populate_dsc_config() to remove 
duplication with the drm_dsc_compute_rc_parameters() (which we already 
use for the MSM DSI DSC).

Not much is left:

dsc->first_line_bpg_offset set via the switch

dsc->line_buf_depth = bpc + 1;
dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
         DSC_MUX_WORD_SIZE_8_10_BPC;

if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
     dsc->nsl_bpg_offset = (2048 *
              (DIV_ROUND_UP(dsc->second_line_bpg_offset,
                                 (dsc->slice_height - 1))));

dsc->initial_scale_value = 8 * dsc->rc_model_size /
                         (dsc->rc_model_size - dsc->initial_offset);


mux_word_size comes from the standard (must)
initial_scale_value calculation is recommended, but not required
nsl_bpg_offset follows the standard (must), also see below (*).

first_line_bpg_offset calculation differs between three drivers. The 
standard also provides a recommended formulas. I think we can leave it 
as is for now.

I think, that mux_word_size and nsl_bpg_offset calculation should be 
moved to drm_dsc_compute_rc_parameters(), while leaving 
initial_scale_value in place (in the driver code).

* I think nsl_bpg_offset is slightly incorrectly calculated. Standard 
demands that it is set to 'second_line_bpg_offset / (slice_height - 1), 
rounded up to 16 fraction bits', while SDE driver code sets it to the 
value rounded up to the next integer (having 16 fraction bits 
representation).

In my opinion correct calculation should be:
dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
                                 (dsc->slice_height - 1));

Could you please check, which one is correct according to the standard?


-- 
With best wishes
Dmitry

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
> On 26/02/2023 02:47, Abhinav Kumar wrote:
>> Hi Dmitry
>>
>> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>>
>>>>
>>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar 
>>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar 
>>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>>> Add DSC helper functions based on DSC configuration profiles 
>>>>>>>>>> to produce
>>>>>>>>>> DSC related runtime parameters through both table look up and 
>>>>>>>>>> runtime
>>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>>
>>>>>>>>>> There are 6 different DSC configuration profiles are supported 
>>>>>>>>>> currently.
>>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC 
>>>>>>>>>> version (V1.1),
>>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>>
>>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>>
>>>>>>>>> These helpers should go to 
>>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>>> Also please check that they can be used for i915 or for amdgpu 
>>>>>>>>> (ideally for both of them).
>>>>>>>>>
>>>>>>>>
>>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based 
>>>>>>>> on the HW core which is being used.
>>>>>>>>
>>>>>>>> They all get packed to the same DSC structure which is the 
>>>>>>>> struct drm_dsc_config but the way the parameters are computed is 
>>>>>>>> specific to the HW.
>>>>>>>>
>>>>>>>> This DPU file helper still uses the drm_dsc_helper's 
>>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but 
>>>>>>>> the parameters themselves are very HW specific and belong to 
>>>>>>>> each vendor's dir.
>>>>>>>>
>>>>>>>> This is not unique to MSM.
>>>>>>>>
>>>>>>>> Lets take a few other examples:
>>>>>>>>
>>>>>>>> AMD: 
>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165 
>>>>>>>>
>>>>>>>>
>>>>>>>> i915: 
>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379 
>>>>>>>>
>>>>>>>
>>>>>>> I checked several values here. Intel driver defines more bpc/bpp 
>>>>>>> combinations, but the ones which are defined in intel_vdsc and in 
>>>>>>> this patch seem to match. If there are major differences there, 
>>>>>>> please point me to the exact case.
>>>>>>>
>>>>>>> I remember that AMD driver might have different values.
>>>>>>>
>>>>>>
>>>>>> Some values in the rc_params table do match. But the 
>>>>>> rc_buf_thresh[] doesnt.
>>>>>
>>>>> Because later they do:
>>>>>
>>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>>
>>>>>>
>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40 
>>>>>>
>>>>>>
>>>>>> Vs
>>>>>>
>>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>>> +};
>>>>>
>>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>>>> standard. As it's done in the Intel driver.
>>>>>
>>>>
>>>> Got it, thanks
>>>>
>>>>>> I dont know the AMD calculation very well to say that moving this 
>>>>>> to the
>>>>>> helper is going to help.
>>>>>
>>>>> Those calculations correspond (more or less) at the first glance to
>>>>> what intel does for their newer generations. I think that's not our
>>>>> problem for now.
>>>>>
>>>>
>>>> Well, we have to figure out if each value matches and if each of 
>>>> them come from the spec for us and i915 and from which section. So 
>>>> it is unfortunately our problem.
>>>
>>> Otherwise it will have to be handled by Marijn, me or anybody else 
>>> wanting to hack up the DSC code. Or by anybody adding DSC support to 
>>> the next platform and having to figure out the difference between 
>>> i915, msm and their platform.
>>>
>>
>> Yes, I wonder why the same doubt didn't arise when the other vendors 
>> added their support both from other maintainers and others.
>>
>> Which makes me think that like I wrote in my previous response, these 
>> are "recommended" values in the spec but its not mandatory.
> 
> I think, it is because there were no other drivers to compare. In other 
> words, for a first driver it is pretty logical to have everything 
> handled on its own. As soon as we start getting other implementations of 
> a feature, it becomes logical to think if the code can be generalized. 
> This is what we see we with the HDCP series or with the code being moved 
> to DP helpers.
> 

We were not the second, MSM was/is the third to add support for DSC afer 
i915 and AMD. Thats what made me think why whoever was the second didnt 
end up generalizing. Was it just missed out or was it intentionally left 
in the vendor driver.

>>
>> Moving this to the drm_dsc_helper is generalizing the tables and not 
>> giving room for the vendors to customize even if they want to (which 
>> the spec does allow).
> 
> That depends on the API you select. For example, in 
> intel_dsc_compute_params() I see customization being applied to 
> rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
> 

Thanks for going through the i915 to figure out that the 6bpp is handled 
in a customized way. So what you are saying is let the helper first fill 
up the recommended values of the spec, whatever is changed from that let 
the vendor driver override that.

Thats where the case-by-case handling comes.

Why not we do this way? Like you mentioned lets move these tables to the 
drm_dsc_helper and let MSM driver first use those.

Then in a separate patchset if i915 and AMD would like to move to that, 
let them handle it for their respective drivers instead of MSM going 
through whats customized for each calculation and doing it.

I am hesitant to take up that effort.

If the recommended values work for the vendor, they can clean it up and 
move to the drm_dsc_helper themselves and preserving their 
customizations rather than one vendor doing it for all of them.

> In case the driver needs to perform customization of the params, nothing 
> stops it drop applying after filling all the RC params in the 
> drm_dsc_config struct via the generic helper.
> 
> 
>> So if this has any merit and if you or Marijn would like to take it 
>> up, go for it. We would do the same thing as either of you would have 
>> to in terms of figuring out the difference between msm and the i915 code.
>>
>> This is not a generic API we are trying to put in a helper, these are 
>> hard-coded tables so there is a difference between looking at these Vs 
>> looking at some common code which can move to the core.
>>
>>>>
>>>>>>
>>>>>> Also, i think its too risky to change other drivers to use 
>>>>>> whatever math
>>>>>> we put in the drm_dsc_helper to compute thr RC params because 
>>>>>> their code
>>>>>> might be computing and using this tables differently.
>>>>>>
>>>>>> Its too much ownership for MSM developers to move this to 
>>>>>> drm_dsc_helper
>>>>>> and own that as it might cause breakage of basic DSC even if some 
>>>>>> values
>>>>>> are repeated.
>>>>>
>>>>> It's time to stop thinking about ownership and start thinking about
>>>>> shared code. We already have two instances of DSC tables. I don't
>>>>> think having a third instance, which is a subset of an existing
>>>>> dataset, would be beneficial to anybody.
>>>>> AMD has complicated code which supports half-bit bpp and calculates
>>>>> some of the parameters. But sharing data with the i915 driver is
>>>>> straightforward.
>>>>>
>>>>
>>>> Sorry, but I would like to get an ack from i915 folks if this is going
>>>> to be useful to them if we move this to helper because we have to 
>>>> look at every table. Not just one.
>>>
>>> Added i915 maintainers to the CC list for them to be able to answer.
>>>
>>
>> Thanks, lets wait to hear from them about where finally these tables 
>> should go but thats can be taken up as a separate effort too.
>>
>>>>
>>>> Also, this is just 1.1, we will add more tables for 1.2. So we will 
>>>> have to end up changing both 1.1 and 1.2 tables as they are 
>>>> different for QC.
>>>
>>> I haven't heard back from Kuogee about the possible causes of using 
>>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on 
>>> that? In other words, can we always stick to the values from 1.2 
>>> standard? What will be the drawback?
>>>
>>> Otherwise, we'd have to have two different sets of values, like you 
>>> do in your vendor driver.
>>>
>>
>> I have responded to this in the other email.
>>
>> All this being said, even if the rc tables move the drm_dsc_helper 
>> either now or later on, we will still need MSM specific calculations 
>> for many of the other encoder parameters (which are again either 
>> hard-coded or calculated). Please refer to the 
>> sde_dsc_populate_dsc_config() downstream. And yes, you will not find 
>> those in the DP spec directly.
>>
>> So we will still need a dsc helper for MSM calculations to be common 
>> for DSI / DP irrespective of where the tables go.
>>
>> So, lets finalize that first.
> 
> I went on and trimmed sde_dsc_populate_dsc_config() to remove 
> duplication with the drm_dsc_compute_rc_parameters() (which we already 
> use for the MSM DSI DSC).
> 
> Not much is left:
> 
> dsc->first_line_bpg_offset set via the switch
> 
> dsc->line_buf_depth = bpc + 1;
> dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
>          DSC_MUX_WORD_SIZE_8_10_BPC;
> 
> if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
>      dsc->nsl_bpg_offset = (2048 *
>               (DIV_ROUND_UP(dsc->second_line_bpg_offset,
>                                  (dsc->slice_height - 1))));
> 
> dsc->initial_scale_value = 8 * dsc->rc_model_size /
>                          (dsc->rc_model_size - dsc->initial_offset);
> 
> 
> mux_word_size comes from the standard (must)
> initial_scale_value calculation is recommended, but not required
> nsl_bpg_offset follows the standard (must), also see below (*).
> 
> first_line_bpg_offset calculation differs between three drivers. The 
> standard also provides a recommended formulas. I think we can leave it 
> as is for now.
> 
> I think, that mux_word_size and nsl_bpg_offset calculation should be 
> moved to drm_dsc_compute_rc_parameters(), while leaving 
> initial_scale_value in place (in the driver code).
> 
> * I think nsl_bpg_offset is slightly incorrectly calculated. Standard 
> demands that it is set to 'second_line_bpg_offset / (slice_height - 1), 
> rounded up to 16 fraction bits', while SDE driver code sets it to the 
> value rounded up to the next integer (having 16 fraction bits 
> representation).
> 
> In my opinion correct calculation should be:
> dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
>                                  (dsc->slice_height - 1));
> 
> Could you please check, which one is correct according to the standard?
> 
> 

Sure, i will check about nsl_bpg_offset. But sorry if I was not more 
clear about this but sde_dsc_populate_dsc_config() is only one example 
which from your analysis can be moved to the drm_dsc_helper() but not 
the initial line calculation _dce_dsc_initial_line_calc(), 
_dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().

All of these are again common between DSI and DP.

So in addition to thinking about what can be moved to the drm_dsc_helper 
also think about what is specific to MSM but common to DSI and DP modules.

That was the bigger picture I was trying to convey.

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Dmitry Baryshkov]

On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
>
>
>
> On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
> > On 26/02/2023 02:47, Abhinav Kumar wrote:
> >> Hi Dmitry
> >>
> >> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
> >>> On 25/02/2023 02:36, Abhinav Kumar wrote:
> >>>>
> >>>>
> >>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
> >>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar
> >>>>> <quic_abhinavk@quicinc.com> wrote:
> >>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
> >>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar
> >>>>>>> <quic_abhinavk@quicinc.com> пишет:
> >>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
> >>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
> >>>>>>>>>> Add DSC helper functions based on DSC configuration profiles
> >>>>>>>>>> to produce
> >>>>>>>>>> DSC related runtime parameters through both table look up and
> >>>>>>>>>> runtime
> >>>>>>>>>> calculation to support DSC on DPU.
> >>>>>>>>>>
> >>>>>>>>>> There are 6 different DSC configuration profiles are supported
> >>>>>>>>>> currently.
> >>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC
> >>>>>>>>>> version (V1.1),
> >>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
> >>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
> >>>>>>>>>>
> >>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
> >>>>>>>>>
> >>>>>>>>> These helpers should go to
> >>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
> >>>>>>>>> Also please check that they can be used for i915 or for amdgpu
> >>>>>>>>> (ideally for both of them).
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based
> >>>>>>>> on the HW core which is being used.
> >>>>>>>>
> >>>>>>>> They all get packed to the same DSC structure which is the
> >>>>>>>> struct drm_dsc_config but the way the parameters are computed is
> >>>>>>>> specific to the HW.
> >>>>>>>>
> >>>>>>>> This DPU file helper still uses the drm_dsc_helper's
> >>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but
> >>>>>>>> the parameters themselves are very HW specific and belong to
> >>>>>>>> each vendor's dir.
> >>>>>>>>
> >>>>>>>> This is not unique to MSM.
> >>>>>>>>
> >>>>>>>> Lets take a few other examples:
> >>>>>>>>
> >>>>>>>> AMD:
> >>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> i915:
> >>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
> >>>>>>>>
> >>>>>>>
> >>>>>>> I checked several values here. Intel driver defines more bpc/bpp
> >>>>>>> combinations, but the ones which are defined in intel_vdsc and in
> >>>>>>> this patch seem to match. If there are major differences there,
> >>>>>>> please point me to the exact case.
> >>>>>>>
> >>>>>>> I remember that AMD driver might have different values.
> >>>>>>>
> >>>>>>
> >>>>>> Some values in the rc_params table do match. But the
> >>>>>> rc_buf_thresh[] doesnt.
> >>>>>
> >>>>> Because later they do:
> >>>>>
> >>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
> >>>>>
> >>>>>>
> >>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
> >>>>>>
> >>>>>>
> >>>>>> Vs
> >>>>>>
> >>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
> >>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
> >>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
> >>>>>> +};
> >>>>>
> >>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
> >>>>> standard. As it's done in the Intel driver.
> >>>>>
> >>>>
> >>>> Got it, thanks
> >>>>
> >>>>>> I dont know the AMD calculation very well to say that moving this
> >>>>>> to the
> >>>>>> helper is going to help.
> >>>>>
> >>>>> Those calculations correspond (more or less) at the first glance to
> >>>>> what intel does for their newer generations. I think that's not our
> >>>>> problem for now.
> >>>>>
> >>>>
> >>>> Well, we have to figure out if each value matches and if each of
> >>>> them come from the spec for us and i915 and from which section. So
> >>>> it is unfortunately our problem.
> >>>
> >>> Otherwise it will have to be handled by Marijn, me or anybody else
> >>> wanting to hack up the DSC code. Or by anybody adding DSC support to
> >>> the next platform and having to figure out the difference between
> >>> i915, msm and their platform.
> >>>
> >>
> >> Yes, I wonder why the same doubt didn't arise when the other vendors
> >> added their support both from other maintainers and others.
> >>
> >> Which makes me think that like I wrote in my previous response, these
> >> are "recommended" values in the spec but its not mandatory.
> >
> > I think, it is because there were no other drivers to compare. In other
> > words, for a first driver it is pretty logical to have everything
> > handled on its own. As soon as we start getting other implementations of
> > a feature, it becomes logical to think if the code can be generalized.
> > This is what we see we with the HDCP series or with the code being moved
> > to DP helpers.
> >
>
> We were not the second, MSM was/is the third to add support for DSC afer
> i915 and AMD. Thats what made me think why whoever was the second didnt
> end up generalizing. Was it just missed out or was it intentionally left
> in the vendor driver.

I didn't count AMD here, since it calculates some of the params rather
than using the fixed ones from the model.

>
> >>
> >> Moving this to the drm_dsc_helper is generalizing the tables and not
> >> giving room for the vendors to customize even if they want to (which
> >> the spec does allow).
> >
> > That depends on the API you select. For example, in
> > intel_dsc_compute_params() I see customization being applied to
> > rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
> >
>
> Thanks for going through the i915 to figure out that the 6bpp is handled
> in a customized way. So what you are saying is let the helper first fill
> up the recommended values of the spec, whatever is changed from that let
> the vendor driver override that.
>
> Thats where the case-by-case handling comes.
>
> Why not we do this way? Like you mentioned lets move these tables to the
> drm_dsc_helper and let MSM driver first use those.
>
> Then in a separate patchset if i915 and AMD would like to move to that,
> let them handle it for their respective drivers instead of MSM going
> through whats customized for each calculation and doing it.
>
> I am hesitant to take up that effort.

Writing a tool to convert model's rc_Nbpc_Mbpp_foo.cfg into C
languages structures used by Intel code took 15-20 minutes. Plugging
generated structures took another 5 minutes. I will send the patches
later today or tomorrow, as I find a time slot to clean them. Thank
you for spending more time on arguing than it took me to generate &
verify the data.

>
> If the recommended values work for the vendor, they can clean it up and
> move to the drm_dsc_helper themselves and preserving their
> customizations rather than one vendor doing it for all of them.
>
> > In case the driver needs to perform customization of the params, nothing
> > stops it drop applying after filling all the RC params in the
> > drm_dsc_config struct via the generic helper.
> >
> >
> >> So if this has any merit and if you or Marijn would like to take it
> >> up, go for it. We would do the same thing as either of you would have
> >> to in terms of figuring out the difference between msm and the i915 code.
> >>
> >> This is not a generic API we are trying to put in a helper, these are
> >> hard-coded tables so there is a difference between looking at these Vs
> >> looking at some common code which can move to the core.
> >>
> >>>>
> >>>>>>
> >>>>>> Also, i think its too risky to change other drivers to use
> >>>>>> whatever math
> >>>>>> we put in the drm_dsc_helper to compute thr RC params because
> >>>>>> their code
> >>>>>> might be computing and using this tables differently.
> >>>>>>
> >>>>>> Its too much ownership for MSM developers to move this to
> >>>>>> drm_dsc_helper
> >>>>>> and own that as it might cause breakage of basic DSC even if some
> >>>>>> values
> >>>>>> are repeated.
> >>>>>
> >>>>> It's time to stop thinking about ownership and start thinking about
> >>>>> shared code. We already have two instances of DSC tables. I don't
> >>>>> think having a third instance, which is a subset of an existing
> >>>>> dataset, would be beneficial to anybody.
> >>>>> AMD has complicated code which supports half-bit bpp and calculates
> >>>>> some of the parameters. But sharing data with the i915 driver is
> >>>>> straightforward.
> >>>>>
> >>>>
> >>>> Sorry, but I would like to get an ack from i915 folks if this is going
> >>>> to be useful to them if we move this to helper because we have to
> >>>> look at every table. Not just one.
> >>>
> >>> Added i915 maintainers to the CC list for them to be able to answer.
> >>>
> >>
> >> Thanks, lets wait to hear from them about where finally these tables
> >> should go but thats can be taken up as a separate effort too.
> >>
> >>>>
> >>>> Also, this is just 1.1, we will add more tables for 1.2. So we will
> >>>> have to end up changing both 1.1 and 1.2 tables as they are
> >>>> different for QC.
> >>>
> >>> I haven't heard back from Kuogee about the possible causes of using
> >>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on
> >>> that? In other words, can we always stick to the values from 1.2
> >>> standard? What will be the drawback?
> >>>
> >>> Otherwise, we'd have to have two different sets of values, like you
> >>> do in your vendor driver.
> >>>
> >>
> >> I have responded to this in the other email.
> >>
> >> All this being said, even if the rc tables move the drm_dsc_helper
> >> either now or later on, we will still need MSM specific calculations
> >> for many of the other encoder parameters (which are again either
> >> hard-coded or calculated). Please refer to the
> >> sde_dsc_populate_dsc_config() downstream. And yes, you will not find
> >> those in the DP spec directly.
> >>
> >> So we will still need a dsc helper for MSM calculations to be common
> >> for DSI / DP irrespective of where the tables go.
> >>
> >> So, lets finalize that first.
> >
> > I went on and trimmed sde_dsc_populate_dsc_config() to remove
> > duplication with the drm_dsc_compute_rc_parameters() (which we already
> > use for the MSM DSI DSC).
> >
> > Not much is left:
> >
> > dsc->first_line_bpg_offset set via the switch
> >
> > dsc->line_buf_depth = bpc + 1;
> > dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
> >          DSC_MUX_WORD_SIZE_8_10_BPC;
> >
> > if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
> >      dsc->nsl_bpg_offset = (2048 *
> >               (DIV_ROUND_UP(dsc->second_line_bpg_offset,
> >                                  (dsc->slice_height - 1))));
> >
> > dsc->initial_scale_value = 8 * dsc->rc_model_size /
> >                          (dsc->rc_model_size - dsc->initial_offset);
> >
> >
> > mux_word_size comes from the standard (must)
> > initial_scale_value calculation is recommended, but not required
> > nsl_bpg_offset follows the standard (must), also see below (*).
> >
> > first_line_bpg_offset calculation differs between three drivers. The
> > standard also provides a recommended formulas. I think we can leave it
> > as is for now.
> >
> > I think, that mux_word_size and nsl_bpg_offset calculation should be
> > moved to drm_dsc_compute_rc_parameters(), while leaving
> > initial_scale_value in place (in the driver code).
> >
> > * I think nsl_bpg_offset is slightly incorrectly calculated. Standard
> > demands that it is set to 'second_line_bpg_offset / (slice_height - 1),
> > rounded up to 16 fraction bits', while SDE driver code sets it to the
> > value rounded up to the next integer (having 16 fraction bits
> > representation).
> >
> > In my opinion correct calculation should be:
> > dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
> >                                  (dsc->slice_height - 1));
> >
> > Could you please check, which one is correct according to the standard?
> >
> >
>
> Sure, i will check about nsl_bpg_offset. But sorry if I was not more
> clear about this but sde_dsc_populate_dsc_config() is only one example
> which from your analysis can be moved to the drm_dsc_helper() but not
> the initial line calculation _dce_dsc_initial_line_calc(),
> _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().

The initial_line is already calculated in dpu_encoder.c. As for the
_dce_dsc_ich_reset_override_needed(), I don't think we support partial
updates in the upstream driver.

>
> All of these are again common between DSI and DP.
>
> So in addition to thinking about what can be moved to the drm_dsc_helper
> also think about what is specific to MSM but common to DSI and DP modules.
>
> That was the bigger picture I was trying to convey.



-- 
With best wishes
Dmitry

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

On 2/27/2023 4:45 AM, Dmitry Baryshkov wrote:
> On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
>>
>>
>>
>> On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
>>> On 26/02/2023 02:47, Abhinav Kumar wrote:
>>>> Hi Dmitry
>>>>
>>>> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>>>>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>>>>
>>>>>>
>>>>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar
>>>>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar
>>>>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>>>>> Add DSC helper functions based on DSC configuration profiles
>>>>>>>>>>>> to produce
>>>>>>>>>>>> DSC related runtime parameters through both table look up and
>>>>>>>>>>>> runtime
>>>>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>>>>
>>>>>>>>>>>> There are 6 different DSC configuration profiles are supported
>>>>>>>>>>>> currently.
>>>>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC
>>>>>>>>>>>> version (V1.1),
>>>>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>>>>
>>>>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>>>>
>>>>>>>>>>> These helpers should go to
>>>>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>>>>> Also please check that they can be used for i915 or for amdgpu
>>>>>>>>>>> (ideally for both of them).
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based
>>>>>>>>>> on the HW core which is being used.
>>>>>>>>>>
>>>>>>>>>> They all get packed to the same DSC structure which is the
>>>>>>>>>> struct drm_dsc_config but the way the parameters are computed is
>>>>>>>>>> specific to the HW.
>>>>>>>>>>
>>>>>>>>>> This DPU file helper still uses the drm_dsc_helper's
>>>>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but
>>>>>>>>>> the parameters themselves are very HW specific and belong to
>>>>>>>>>> each vendor's dir.
>>>>>>>>>>
>>>>>>>>>> This is not unique to MSM.
>>>>>>>>>>
>>>>>>>>>> Lets take a few other examples:
>>>>>>>>>>
>>>>>>>>>> AMD:
>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> i915:
>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I checked several values here. Intel driver defines more bpc/bpp
>>>>>>>>> combinations, but the ones which are defined in intel_vdsc and in
>>>>>>>>> this patch seem to match. If there are major differences there,
>>>>>>>>> please point me to the exact case.
>>>>>>>>>
>>>>>>>>> I remember that AMD driver might have different values.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Some values in the rc_params table do match. But the
>>>>>>>> rc_buf_thresh[] doesnt.
>>>>>>>
>>>>>>> Because later they do:
>>>>>>>
>>>>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>>>>
>>>>>>>>
>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
>>>>>>>>
>>>>>>>>
>>>>>>>> Vs
>>>>>>>>
>>>>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>>>>> +};
>>>>>>>
>>>>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>>>>>> standard. As it's done in the Intel driver.
>>>>>>>
>>>>>>
>>>>>> Got it, thanks
>>>>>>
>>>>>>>> I dont know the AMD calculation very well to say that moving this
>>>>>>>> to the
>>>>>>>> helper is going to help.
>>>>>>>
>>>>>>> Those calculations correspond (more or less) at the first glance to
>>>>>>> what intel does for their newer generations. I think that's not our
>>>>>>> problem for now.
>>>>>>>
>>>>>>
>>>>>> Well, we have to figure out if each value matches and if each of
>>>>>> them come from the spec for us and i915 and from which section. So
>>>>>> it is unfortunately our problem.
>>>>>
>>>>> Otherwise it will have to be handled by Marijn, me or anybody else
>>>>> wanting to hack up the DSC code. Or by anybody adding DSC support to
>>>>> the next platform and having to figure out the difference between
>>>>> i915, msm and their platform.
>>>>>
>>>>
>>>> Yes, I wonder why the same doubt didn't arise when the other vendors
>>>> added their support both from other maintainers and others.
>>>>
>>>> Which makes me think that like I wrote in my previous response, these
>>>> are "recommended" values in the spec but its not mandatory.
>>>
>>> I think, it is because there were no other drivers to compare. In other
>>> words, for a first driver it is pretty logical to have everything
>>> handled on its own. As soon as we start getting other implementations of
>>> a feature, it becomes logical to think if the code can be generalized.
>>> This is what we see we with the HDCP series or with the code being moved
>>> to DP helpers.
>>>
>>
>> We were not the second, MSM was/is the third to add support for DSC afer
>> i915 and AMD. Thats what made me think why whoever was the second didnt
>> end up generalizing. Was it just missed out or was it intentionally left
>> in the vendor driver.
> 
> I didn't count AMD here, since it calculates some of the params rather
> than using the fixed ones from the model.
> 
>>
>>>>
>>>> Moving this to the drm_dsc_helper is generalizing the tables and not
>>>> giving room for the vendors to customize even if they want to (which
>>>> the spec does allow).
>>>
>>> That depends on the API you select. For example, in
>>> intel_dsc_compute_params() I see customization being applied to
>>> rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
>>>
>>
>> Thanks for going through the i915 to figure out that the 6bpp is handled
>> in a customized way. So what you are saying is let the helper first fill
>> up the recommended values of the spec, whatever is changed from that let
>> the vendor driver override that.
>>
>> Thats where the case-by-case handling comes.
>>
>> Why not we do this way? Like you mentioned lets move these tables to the
>> drm_dsc_helper and let MSM driver first use those.
>>
>> Then in a separate patchset if i915 and AMD would like to move to that,
>> let them handle it for their respective drivers instead of MSM going
>> through whats customized for each calculation and doing it.
>>
>> I am hesitant to take up that effort.
> 
> Writing a tool to convert model's rc_Nbpc_Mbpp_foo.cfg into C
> languages structures used by Intel code took 15-20 minutes. Plugging
> generated structures took another 5 minutes. I will send the patches
> later today or tomorrow, as I find a time slot to clean them. Thank
> you for spending more time on arguing than it took me to generate &
> verify the data.
> 

Great, we will wait for your patches. We didnt intend to spend time on 
this at this point. We always wanted to take it up in a separate series 
of moving the tables.

You preferred not to wait. Upto you.

So thanks for doing it.

>>
>> If the recommended values work for the vendor, they can clean it up and
>> move to the drm_dsc_helper themselves and preserving their
>> customizations rather than one vendor doing it for all of them.
>>
>>> In case the driver needs to perform customization of the params, nothing
>>> stops it drop applying after filling all the RC params in the
>>> drm_dsc_config struct via the generic helper.
>>>
>>>
>>>> So if this has any merit and if you or Marijn would like to take it
>>>> up, go for it. We would do the same thing as either of you would have
>>>> to in terms of figuring out the difference between msm and the i915 code.
>>>>
>>>> This is not a generic API we are trying to put in a helper, these are
>>>> hard-coded tables so there is a difference between looking at these Vs
>>>> looking at some common code which can move to the core.
>>>>
>>>>>>
>>>>>>>>
>>>>>>>> Also, i think its too risky to change other drivers to use
>>>>>>>> whatever math
>>>>>>>> we put in the drm_dsc_helper to compute thr RC params because
>>>>>>>> their code
>>>>>>>> might be computing and using this tables differently.
>>>>>>>>
>>>>>>>> Its too much ownership for MSM developers to move this to
>>>>>>>> drm_dsc_helper
>>>>>>>> and own that as it might cause breakage of basic DSC even if some
>>>>>>>> values
>>>>>>>> are repeated.
>>>>>>>
>>>>>>> It's time to stop thinking about ownership and start thinking about
>>>>>>> shared code. We already have two instances of DSC tables. I don't
>>>>>>> think having a third instance, which is a subset of an existing
>>>>>>> dataset, would be beneficial to anybody.
>>>>>>> AMD has complicated code which supports half-bit bpp and calculates
>>>>>>> some of the parameters. But sharing data with the i915 driver is
>>>>>>> straightforward.
>>>>>>>
>>>>>>
>>>>>> Sorry, but I would like to get an ack from i915 folks if this is going
>>>>>> to be useful to them if we move this to helper because we have to
>>>>>> look at every table. Not just one.
>>>>>
>>>>> Added i915 maintainers to the CC list for them to be able to answer.
>>>>>
>>>>
>>>> Thanks, lets wait to hear from them about where finally these tables
>>>> should go but thats can be taken up as a separate effort too.
>>>>
>>>>>>
>>>>>> Also, this is just 1.1, we will add more tables for 1.2. So we will
>>>>>> have to end up changing both 1.1 and 1.2 tables as they are
>>>>>> different for QC.
>>>>>
>>>>> I haven't heard back from Kuogee about the possible causes of using
>>>>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on
>>>>> that? In other words, can we always stick to the values from 1.2
>>>>> standard? What will be the drawback?
>>>>>
>>>>> Otherwise, we'd have to have two different sets of values, like you
>>>>> do in your vendor driver.
>>>>>
>>>>
>>>> I have responded to this in the other email.
>>>>
>>>> All this being said, even if the rc tables move the drm_dsc_helper
>>>> either now or later on, we will still need MSM specific calculations
>>>> for many of the other encoder parameters (which are again either
>>>> hard-coded or calculated). Please refer to the
>>>> sde_dsc_populate_dsc_config() downstream. And yes, you will not find
>>>> those in the DP spec directly.
>>>>
>>>> So we will still need a dsc helper for MSM calculations to be common
>>>> for DSI / DP irrespective of where the tables go.
>>>>
>>>> So, lets finalize that first.
>>>
>>> I went on and trimmed sde_dsc_populate_dsc_config() to remove
>>> duplication with the drm_dsc_compute_rc_parameters() (which we already
>>> use for the MSM DSI DSC).
>>>
>>> Not much is left:
>>>
>>> dsc->first_line_bpg_offset set via the switch
>>>
>>> dsc->line_buf_depth = bpc + 1;
>>> dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
>>>           DSC_MUX_WORD_SIZE_8_10_BPC;
>>>
>>> if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
>>>       dsc->nsl_bpg_offset = (2048 *
>>>                (DIV_ROUND_UP(dsc->second_line_bpg_offset,
>>>                                   (dsc->slice_height - 1))));
>>>
>>> dsc->initial_scale_value = 8 * dsc->rc_model_size /
>>>                           (dsc->rc_model_size - dsc->initial_offset);
>>>
>>>
>>> mux_word_size comes from the standard (must)
>>> initial_scale_value calculation is recommended, but not required
>>> nsl_bpg_offset follows the standard (must), also see below (*).
>>>
>>> first_line_bpg_offset calculation differs between three drivers. The
>>> standard also provides a recommended formulas. I think we can leave it
>>> as is for now.
>>>
>>> I think, that mux_word_size and nsl_bpg_offset calculation should be
>>> moved to drm_dsc_compute_rc_parameters(), while leaving
>>> initial_scale_value in place (in the driver code).
>>>
>>> * I think nsl_bpg_offset is slightly incorrectly calculated. Standard
>>> demands that it is set to 'second_line_bpg_offset / (slice_height - 1),
>>> rounded up to 16 fraction bits', while SDE driver code sets it to the
>>> value rounded up to the next integer (having 16 fraction bits
>>> representation).
>>>
>>> In my opinion correct calculation should be:
>>> dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
>>>                                   (dsc->slice_height - 1));
>>>
>>> Could you please check, which one is correct according to the standard?
>>>
>>>
>>
>> Sure, i will check about nsl_bpg_offset. But sorry if I was not more
>> clear about this but sde_dsc_populate_dsc_config() is only one example
>> which from your analysis can be moved to the drm_dsc_helper() but not
>> the initial line calculation _dce_dsc_initial_line_calc(),
>> _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().
> 
> The initial_line is already calculated in dpu_encoder.c. As for the
> _dce_dsc_ich_reset_override_needed(), I don't think we support partial
> updates in the upstream driver.
> 
>>
>> All of these are again common between DSI and DP.
>>
>> So in addition to thinking about what can be moved to the drm_dsc_helper
>> also think about what is specific to MSM but common to DSI and DP modules.
>>
>> That was the bigger picture I was trying to convey.
> 

_dce_dsc_initial_line_calc which will get expanded with v1.2 gets added 
has much more than whats there in upstream today.

Dumping everything in dpu_encoder is not the solution. Sorry.

> 
> 

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Dmitry Baryshkov]

27 февраля 2023 г. 19:59:35 GMT+02:00, Abhinav Kumar <quic_abhinavk@quicinc.com> пишет:
>
>
>On 2/27/2023 4:45 AM, Dmitry Baryshkov wrote:
>> On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
>>> 
>>> 
>>> 
>>> On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
>>>> On 26/02/2023 02:47, Abhinav Kumar wrote:
>>>>> Hi Dmitry
>>>>> 
>>>>> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>>>>>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>>>>> 
>>>>>>> 
>>>>>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>>>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar
>>>>>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar
>>>>>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>>>>>> Add DSC helper functions based on DSC configuration profiles
>>>>>>>>>>>>> to produce
>>>>>>>>>>>>> DSC related runtime parameters through both table look up and
>>>>>>>>>>>>> runtime
>>>>>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> There are 6 different DSC configuration profiles are supported
>>>>>>>>>>>>> currently.
>>>>>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC
>>>>>>>>>>>>> version (V1.1),
>>>>>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>>>>> 
>>>>>>>>>>>> These helpers should go to
>>>>>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>>>>>> Also please check that they can be used for i915 or for amdgpu
>>>>>>>>>>>> (ideally for both of them).
>>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based
>>>>>>>>>>> on the HW core which is being used.
>>>>>>>>>>> 
>>>>>>>>>>> They all get packed to the same DSC structure which is the
>>>>>>>>>>> struct drm_dsc_config but the way the parameters are computed is
>>>>>>>>>>> specific to the HW.
>>>>>>>>>>> 
>>>>>>>>>>> This DPU file helper still uses the drm_dsc_helper's
>>>>>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but
>>>>>>>>>>> the parameters themselves are very HW specific and belong to
>>>>>>>>>>> each vendor's dir.
>>>>>>>>>>> 
>>>>>>>>>>> This is not unique to MSM.
>>>>>>>>>>> 
>>>>>>>>>>> Lets take a few other examples:
>>>>>>>>>>> 
>>>>>>>>>>> AMD:
>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> i915:
>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
>>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> I checked several values here. Intel driver defines more bpc/bpp
>>>>>>>>>> combinations, but the ones which are defined in intel_vdsc and in
>>>>>>>>>> this patch seem to match. If there are major differences there,
>>>>>>>>>> please point me to the exact case.
>>>>>>>>>> 
>>>>>>>>>> I remember that AMD driver might have different values.
>>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> Some values in the rc_params table do match. But the
>>>>>>>>> rc_buf_thresh[] doesnt.
>>>>>>>> 
>>>>>>>> Because later they do:
>>>>>>>> 
>>>>>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> Vs
>>>>>>>>> 
>>>>>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>>>>>> +};
>>>>>>>> 
>>>>>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>>>>>>> standard. As it's done in the Intel driver.
>>>>>>>> 
>>>>>>> 
>>>>>>> Got it, thanks
>>>>>>> 
>>>>>>>>> I dont know the AMD calculation very well to say that moving this
>>>>>>>>> to the
>>>>>>>>> helper is going to help.
>>>>>>>> 
>>>>>>>> Those calculations correspond (more or less) at the first glance to
>>>>>>>> what intel does for their newer generations. I think that's not our
>>>>>>>> problem for now.
>>>>>>>> 
>>>>>>> 
>>>>>>> Well, we have to figure out if each value matches and if each of
>>>>>>> them come from the spec for us and i915 and from which section. So
>>>>>>> it is unfortunately our problem.
>>>>>> 
>>>>>> Otherwise it will have to be handled by Marijn, me or anybody else
>>>>>> wanting to hack up the DSC code. Or by anybody adding DSC support to
>>>>>> the next platform and having to figure out the difference between
>>>>>> i915, msm and their platform.
>>>>>> 
>>>>> 
>>>>> Yes, I wonder why the same doubt didn't arise when the other vendors
>>>>> added their support both from other maintainers and others.
>>>>> 
>>>>> Which makes me think that like I wrote in my previous response, these
>>>>> are "recommended" values in the spec but its not mandatory.
>>>> 
>>>> I think, it is because there were no other drivers to compare. In other
>>>> words, for a first driver it is pretty logical to have everything
>>>> handled on its own. As soon as we start getting other implementations of
>>>> a feature, it becomes logical to think if the code can be generalized.
>>>> This is what we see we with the HDCP series or with the code being moved
>>>> to DP helpers.
>>>> 
>>> 
>>> We were not the second, MSM was/is the third to add support for DSC afer
>>> i915 and AMD. Thats what made me think why whoever was the second didnt
>>> end up generalizing. Was it just missed out or was it intentionally left
>>> in the vendor driver.
>> 
>> I didn't count AMD here, since it calculates some of the params rather
>> than using the fixed ones from the model.
>> 
>>> 
>>>>> 
>>>>> Moving this to the drm_dsc_helper is generalizing the tables and not
>>>>> giving room for the vendors to customize even if they want to (which
>>>>> the spec does allow).
>>>> 
>>>> That depends on the API you select. For example, in
>>>> intel_dsc_compute_params() I see customization being applied to
>>>> rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
>>>> 
>>> 
>>> Thanks for going through the i915 to figure out that the 6bpp is handled
>>> in a customized way. So what you are saying is let the helper first fill
>>> up the recommended values of the spec, whatever is changed from that let
>>> the vendor driver override that.
>>> 
>>> Thats where the case-by-case handling comes.
>>> 
>>> Why not we do this way? Like you mentioned lets move these tables to the
>>> drm_dsc_helper and let MSM driver first use those.
>>> 
>>> Then in a separate patchset if i915 and AMD would like to move to that,
>>> let them handle it for their respective drivers instead of MSM going
>>> through whats customized for each calculation and doing it.
>>> 
>>> I am hesitant to take up that effort.
>> 
>> Writing a tool to convert model's rc_Nbpc_Mbpp_foo.cfg into C
>> languages structures used by Intel code took 15-20 minutes. Plugging
>> generated structures took another 5 minutes. I will send the patches
>> later today or tomorrow, as I find a time slot to clean them. Thank
>> you for spending more time on arguing than it took me to generate &
>> verify the data.
>> 
>
>Great, we will wait for your patches. We didnt intend to spend time on this at this point. We always wanted to take it up in a separate series of moving the tables.

Getting rid of msm_display_dsc_config and then making use of drm_dsc_compute_rc_parameters() was bad enough. So, let's get things done in a good way now, rather than at some random point later.


>
>You preferred not to wait. Upto you.
>
>So thanks for doing it.
>
>>> 
>>> If the recommended values work for the vendor, they can clean it up and
>>> move to the drm_dsc_helper themselves and preserving their
>>> customizations rather than one vendor doing it for all of them.
>>> 
>>>> In case the driver needs to perform customization of the params, nothing
>>>> stops it drop applying after filling all the RC params in the
>>>> drm_dsc_config struct via the generic helper.
>>>> 
>>>> 
>>>>> So if this has any merit and if you or Marijn would like to take it
>>>>> up, go for it. We would do the same thing as either of you would have
>>>>> to in terms of figuring out the difference between msm and the i915 code.
>>>>> 
>>>>> This is not a generic API we are trying to put in a helper, these are
>>>>> hard-coded tables so there is a difference between looking at these Vs
>>>>> looking at some common code which can move to the core.
>>>>> 
>>>>>>> 
>>>>>>>>> 
>>>>>>>>> Also, i think its too risky to change other drivers to use
>>>>>>>>> whatever math
>>>>>>>>> we put in the drm_dsc_helper to compute thr RC params because
>>>>>>>>> their code
>>>>>>>>> might be computing and using this tables differently.
>>>>>>>>> 
>>>>>>>>> Its too much ownership for MSM developers to move this to
>>>>>>>>> drm_dsc_helper
>>>>>>>>> and own that as it might cause breakage of basic DSC even if some
>>>>>>>>> values
>>>>>>>>> are repeated.
>>>>>>>> 
>>>>>>>> It's time to stop thinking about ownership and start thinking about
>>>>>>>> shared code. We already have two instances of DSC tables. I don't
>>>>>>>> think having a third instance, which is a subset of an existing
>>>>>>>> dataset, would be beneficial to anybody.
>>>>>>>> AMD has complicated code which supports half-bit bpp and calculates
>>>>>>>> some of the parameters. But sharing data with the i915 driver is
>>>>>>>> straightforward.
>>>>>>>> 
>>>>>>> 
>>>>>>> Sorry, but I would like to get an ack from i915 folks if this is going
>>>>>>> to be useful to them if we move this to helper because we have to
>>>>>>> look at every table. Not just one.
>>>>>> 
>>>>>> Added i915 maintainers to the CC list for them to be able to answer.
>>>>>> 
>>>>> 
>>>>> Thanks, lets wait to hear from them about where finally these tables
>>>>> should go but thats can be taken up as a separate effort too.
>>>>> 
>>>>>>> 
>>>>>>> Also, this is just 1.1, we will add more tables for 1.2. So we will
>>>>>>> have to end up changing both 1.1 and 1.2 tables as they are
>>>>>>> different for QC.
>>>>>> 
>>>>>> I haven't heard back from Kuogee about the possible causes of using
>>>>>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on
>>>>>> that? In other words, can we always stick to the values from 1.2
>>>>>> standard? What will be the drawback?
>>>>>> 
>>>>>> Otherwise, we'd have to have two different sets of values, like you
>>>>>> do in your vendor driver.
>>>>>> 
>>>>> 
>>>>> I have responded to this in the other email.
>>>>> 
>>>>> All this being said, even if the rc tables move the drm_dsc_helper
>>>>> either now or later on, we will still need MSM specific calculations
>>>>> for many of the other encoder parameters (which are again either
>>>>> hard-coded or calculated). Please refer to the
>>>>> sde_dsc_populate_dsc_config() downstream. And yes, you will not find
>>>>> those in the DP spec directly.
>>>>> 
>>>>> So we will still need a dsc helper for MSM calculations to be common
>>>>> for DSI / DP irrespective of where the tables go.
>>>>> 
>>>>> So, lets finalize that first.
>>>> 
>>>> I went on and trimmed sde_dsc_populate_dsc_config() to remove
>>>> duplication with the drm_dsc_compute_rc_parameters() (which we already
>>>> use for the MSM DSI DSC).
>>>> 
>>>> Not much is left:
>>>> 
>>>> dsc->first_line_bpg_offset set via the switch
>>>> 
>>>> dsc->line_buf_depth = bpc + 1;
>>>> dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
>>>>           DSC_MUX_WORD_SIZE_8_10_BPC;
>>>> 
>>>> if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
>>>>       dsc->nsl_bpg_offset = (2048 *
>>>>                (DIV_ROUND_UP(dsc->second_line_bpg_offset,
>>>>                                   (dsc->slice_height - 1))));
>>>> 
>>>> dsc->initial_scale_value = 8 * dsc->rc_model_size /
>>>>                           (dsc->rc_model_size - dsc->initial_offset);
>>>> 
>>>> 
>>>> mux_word_size comes from the standard (must)
>>>> initial_scale_value calculation is recommended, but not required
>>>> nsl_bpg_offset follows the standard (must), also see below (*).
>>>> 
>>>> first_line_bpg_offset calculation differs between three drivers. The
>>>> standard also provides a recommended formulas. I think we can leave it
>>>> as is for now.
>>>> 
>>>> I think, that mux_word_size and nsl_bpg_offset calculation should be
>>>> moved to drm_dsc_compute_rc_parameters(), while leaving
>>>> initial_scale_value in place (in the driver code).
>>>> 
>>>> * I think nsl_bpg_offset is slightly incorrectly calculated. Standard
>>>> demands that it is set to 'second_line_bpg_offset / (slice_height - 1),
>>>> rounded up to 16 fraction bits', while SDE driver code sets it to the
>>>> value rounded up to the next integer (having 16 fraction bits
>>>> representation).
>>>> 
>>>> In my opinion correct calculation should be:
>>>> dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
>>>>                                   (dsc->slice_height - 1));
>>>> 
>>>> Could you please check, which one is correct according to the standard?
>>>> 
>>>> 
>>> 
>>> Sure, i will check about nsl_bpg_offset. But sorry if I was not more
>>> clear about this but sde_dsc_populate_dsc_config() is only one example
>>> which from your analysis can be moved to the drm_dsc_helper() but not
>>> the initial line calculation _dce_dsc_initial_line_calc(),
>>> _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().
>> 
>> The initial_line is already calculated in dpu_encoder.c. As for the
>> _dce_dsc_ich_reset_override_needed(), I don't think we support partial
>> updates in the upstream driver.
>> 
>>> 
>>> All of these are again common between DSI and DP.
>>> 
>>> So in addition to thinking about what can be moved to the drm_dsc_helper
>>> also think about what is specific to MSM but common to DSI and DP modules.
>>> 
>>> That was the bigger picture I was trying to convey.
>> 
>
>_dce_dsc_initial_line_calc which will get expanded with v1.2 gets added has much more than whats there in upstream today.
>
>Dumping everything in dpu_encoder is not the solution. Sorry.

But it is still the DPU thing. So, no problems.

>
>> 
>> 

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

On 2/27/2023 11:25 AM, Dmitry Baryshkov wrote:
> 27 февраля 2023 г. 19:59:35 GMT+02:00, Abhinav Kumar <quic_abhinavk@quicinc.com> пишет:
>>
>>
>> On 2/27/2023 4:45 AM, Dmitry Baryshkov wrote:
>>> On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
>>>>
>>>>
>>>>
>>>> On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
>>>>> On 26/02/2023 02:47, Abhinav Kumar wrote:
>>>>>> Hi Dmitry
>>>>>>
>>>>>> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>>>>>>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>>>>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar
>>>>>>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar
>>>>>>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>>>>>>> Add DSC helper functions based on DSC configuration profiles
>>>>>>>>>>>>>> to produce
>>>>>>>>>>>>>> DSC related runtime parameters through both table look up and
>>>>>>>>>>>>>> runtime
>>>>>>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> There are 6 different DSC configuration profiles are supported
>>>>>>>>>>>>>> currently.
>>>>>>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC
>>>>>>>>>>>>>> version (V1.1),
>>>>>>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>>>>>>
>>>>>>>>>>>>> These helpers should go to
>>>>>>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>>>>>>> Also please check that they can be used for i915 or for amdgpu
>>>>>>>>>>>>> (ideally for both of them).
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based
>>>>>>>>>>>> on the HW core which is being used.
>>>>>>>>>>>>
>>>>>>>>>>>> They all get packed to the same DSC structure which is the
>>>>>>>>>>>> struct drm_dsc_config but the way the parameters are computed is
>>>>>>>>>>>> specific to the HW.
>>>>>>>>>>>>
>>>>>>>>>>>> This DPU file helper still uses the drm_dsc_helper's
>>>>>>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but
>>>>>>>>>>>> the parameters themselves are very HW specific and belong to
>>>>>>>>>>>> each vendor's dir.
>>>>>>>>>>>>
>>>>>>>>>>>> This is not unique to MSM.
>>>>>>>>>>>>
>>>>>>>>>>>> Lets take a few other examples:
>>>>>>>>>>>>
>>>>>>>>>>>> AMD:
>>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> i915:
>>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> I checked several values here. Intel driver defines more bpc/bpp
>>>>>>>>>>> combinations, but the ones which are defined in intel_vdsc and in
>>>>>>>>>>> this patch seem to match. If there are major differences there,
>>>>>>>>>>> please point me to the exact case.
>>>>>>>>>>>
>>>>>>>>>>> I remember that AMD driver might have different values.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Some values in the rc_params table do match. But the
>>>>>>>>>> rc_buf_thresh[] doesnt.
>>>>>>>>>
>>>>>>>>> Because later they do:
>>>>>>>>>
>>>>>>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Vs
>>>>>>>>>>
>>>>>>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>>>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>>>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>>>>>>> +};
>>>>>>>>>
>>>>>>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>>>>>>>> standard. As it's done in the Intel driver.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Got it, thanks
>>>>>>>>
>>>>>>>>>> I dont know the AMD calculation very well to say that moving this
>>>>>>>>>> to the
>>>>>>>>>> helper is going to help.
>>>>>>>>>
>>>>>>>>> Those calculations correspond (more or less) at the first glance to
>>>>>>>>> what intel does for their newer generations. I think that's not our
>>>>>>>>> problem for now.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Well, we have to figure out if each value matches and if each of
>>>>>>>> them come from the spec for us and i915 and from which section. So
>>>>>>>> it is unfortunately our problem.
>>>>>>>
>>>>>>> Otherwise it will have to be handled by Marijn, me or anybody else
>>>>>>> wanting to hack up the DSC code. Or by anybody adding DSC support to
>>>>>>> the next platform and having to figure out the difference between
>>>>>>> i915, msm and their platform.
>>>>>>>
>>>>>>
>>>>>> Yes, I wonder why the same doubt didn't arise when the other vendors
>>>>>> added their support both from other maintainers and others.
>>>>>>
>>>>>> Which makes me think that like I wrote in my previous response, these
>>>>>> are "recommended" values in the spec but its not mandatory.
>>>>>
>>>>> I think, it is because there were no other drivers to compare. In other
>>>>> words, for a first driver it is pretty logical to have everything
>>>>> handled on its own. As soon as we start getting other implementations of
>>>>> a feature, it becomes logical to think if the code can be generalized.
>>>>> This is what we see we with the HDCP series or with the code being moved
>>>>> to DP helpers.
>>>>>
>>>>
>>>> We were not the second, MSM was/is the third to add support for DSC afer
>>>> i915 and AMD. Thats what made me think why whoever was the second didnt
>>>> end up generalizing. Was it just missed out or was it intentionally left
>>>> in the vendor driver.
>>>
>>> I didn't count AMD here, since it calculates some of the params rather
>>> than using the fixed ones from the model.
>>>
>>>>
>>>>>>
>>>>>> Moving this to the drm_dsc_helper is generalizing the tables and not
>>>>>> giving room for the vendors to customize even if they want to (which
>>>>>> the spec does allow).
>>>>>
>>>>> That depends on the API you select. For example, in
>>>>> intel_dsc_compute_params() I see customization being applied to
>>>>> rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
>>>>>
>>>>
>>>> Thanks for going through the i915 to figure out that the 6bpp is handled
>>>> in a customized way. So what you are saying is let the helper first fill
>>>> up the recommended values of the spec, whatever is changed from that let
>>>> the vendor driver override that.
>>>>
>>>> Thats where the case-by-case handling comes.
>>>>
>>>> Why not we do this way? Like you mentioned lets move these tables to the
>>>> drm_dsc_helper and let MSM driver first use those.
>>>>
>>>> Then in a separate patchset if i915 and AMD would like to move to that,
>>>> let them handle it for their respective drivers instead of MSM going
>>>> through whats customized for each calculation and doing it.
>>>>
>>>> I am hesitant to take up that effort.
>>>
>>> Writing a tool to convert model's rc_Nbpc_Mbpp_foo.cfg into C
>>> languages structures used by Intel code took 15-20 minutes. Plugging
>>> generated structures took another 5 minutes. I will send the patches
>>> later today or tomorrow, as I find a time slot to clean them. Thank
>>> you for spending more time on arguing than it took me to generate &
>>> verify the data.
>>>
>>
>> Great, we will wait for your patches. We didnt intend to spend time on this at this point. We always wanted to take it up in a separate series of moving the tables.
> 
> Getting rid of msm_display_dsc_config and then making use of drm_dsc_compute_rc_parameters() was bad enough. So, let's get things done in a good way now, rather than at some random point later.
> 

Alright, we will wait for your change then :)

> 
>>
>> You preferred not to wait. Upto you.
>>
>> So thanks for doing it.
>>
>>>>
>>>> If the recommended values work for the vendor, they can clean it up and
>>>> move to the drm_dsc_helper themselves and preserving their
>>>> customizations rather than one vendor doing it for all of them.
>>>>
>>>>> In case the driver needs to perform customization of the params, nothing
>>>>> stops it drop applying after filling all the RC params in the
>>>>> drm_dsc_config struct via the generic helper.
>>>>>
>>>>>
>>>>>> So if this has any merit and if you or Marijn would like to take it
>>>>>> up, go for it. We would do the same thing as either of you would have
>>>>>> to in terms of figuring out the difference between msm and the i915 code.
>>>>>>
>>>>>> This is not a generic API we are trying to put in a helper, these are
>>>>>> hard-coded tables so there is a difference between looking at these Vs
>>>>>> looking at some common code which can move to the core.
>>>>>>
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Also, i think its too risky to change other drivers to use
>>>>>>>>>> whatever math
>>>>>>>>>> we put in the drm_dsc_helper to compute thr RC params because
>>>>>>>>>> their code
>>>>>>>>>> might be computing and using this tables differently.
>>>>>>>>>>
>>>>>>>>>> Its too much ownership for MSM developers to move this to
>>>>>>>>>> drm_dsc_helper
>>>>>>>>>> and own that as it might cause breakage of basic DSC even if some
>>>>>>>>>> values
>>>>>>>>>> are repeated.
>>>>>>>>>
>>>>>>>>> It's time to stop thinking about ownership and start thinking about
>>>>>>>>> shared code. We already have two instances of DSC tables. I don't
>>>>>>>>> think having a third instance, which is a subset of an existing
>>>>>>>>> dataset, would be beneficial to anybody.
>>>>>>>>> AMD has complicated code which supports half-bit bpp and calculates
>>>>>>>>> some of the parameters. But sharing data with the i915 driver is
>>>>>>>>> straightforward.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Sorry, but I would like to get an ack from i915 folks if this is going
>>>>>>>> to be useful to them if we move this to helper because we have to
>>>>>>>> look at every table. Not just one.
>>>>>>>
>>>>>>> Added i915 maintainers to the CC list for them to be able to answer.
>>>>>>>
>>>>>>
>>>>>> Thanks, lets wait to hear from them about where finally these tables
>>>>>> should go but thats can be taken up as a separate effort too.
>>>>>>
>>>>>>>>
>>>>>>>> Also, this is just 1.1, we will add more tables for 1.2. So we will
>>>>>>>> have to end up changing both 1.1 and 1.2 tables as they are
>>>>>>>> different for QC.
>>>>>>>
>>>>>>> I haven't heard back from Kuogee about the possible causes of using
>>>>>>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on
>>>>>>> that? In other words, can we always stick to the values from 1.2
>>>>>>> standard? What will be the drawback?
>>>>>>>
>>>>>>> Otherwise, we'd have to have two different sets of values, like you
>>>>>>> do in your vendor driver.
>>>>>>>
>>>>>>
>>>>>> I have responded to this in the other email.
>>>>>>
>>>>>> All this being said, even if the rc tables move the drm_dsc_helper
>>>>>> either now or later on, we will still need MSM specific calculations
>>>>>> for many of the other encoder parameters (which are again either
>>>>>> hard-coded or calculated). Please refer to the
>>>>>> sde_dsc_populate_dsc_config() downstream. And yes, you will not find
>>>>>> those in the DP spec directly.
>>>>>>
>>>>>> So we will still need a dsc helper for MSM calculations to be common
>>>>>> for DSI / DP irrespective of where the tables go.
>>>>>>
>>>>>> So, lets finalize that first.
>>>>>
>>>>> I went on and trimmed sde_dsc_populate_dsc_config() to remove
>>>>> duplication with the drm_dsc_compute_rc_parameters() (which we already
>>>>> use for the MSM DSI DSC).
>>>>>
>>>>> Not much is left:
>>>>>
>>>>> dsc->first_line_bpg_offset set via the switch
>>>>>
>>>>> dsc->line_buf_depth = bpc + 1;
>>>>> dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
>>>>>            DSC_MUX_WORD_SIZE_8_10_BPC;
>>>>>
>>>>> if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
>>>>>        dsc->nsl_bpg_offset = (2048 *
>>>>>                 (DIV_ROUND_UP(dsc->second_line_bpg_offset,
>>>>>                                    (dsc->slice_height - 1))));
>>>>>
>>>>> dsc->initial_scale_value = 8 * dsc->rc_model_size /
>>>>>                            (dsc->rc_model_size - dsc->initial_offset);
>>>>>
>>>>>
>>>>> mux_word_size comes from the standard (must)
>>>>> initial_scale_value calculation is recommended, but not required
>>>>> nsl_bpg_offset follows the standard (must), also see below (*).
>>>>>
>>>>> first_line_bpg_offset calculation differs between three drivers. The
>>>>> standard also provides a recommended formulas. I think we can leave it
>>>>> as is for now.
>>>>>
>>>>> I think, that mux_word_size and nsl_bpg_offset calculation should be
>>>>> moved to drm_dsc_compute_rc_parameters(), while leaving
>>>>> initial_scale_value in place (in the driver code).
>>>>>
>>>>> * I think nsl_bpg_offset is slightly incorrectly calculated. Standard
>>>>> demands that it is set to 'second_line_bpg_offset / (slice_height - 1),
>>>>> rounded up to 16 fraction bits', while SDE driver code sets it to the
>>>>> value rounded up to the next integer (having 16 fraction bits
>>>>> representation).
>>>>>
>>>>> In my opinion correct calculation should be:
>>>>> dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
>>>>>                                    (dsc->slice_height - 1));
>>>>>
>>>>> Could you please check, which one is correct according to the standard?
>>>>>
>>>>>
>>>>
>>>> Sure, i will check about nsl_bpg_offset. But sorry if I was not more
>>>> clear about this but sde_dsc_populate_dsc_config() is only one example
>>>> which from your analysis can be moved to the drm_dsc_helper() but not
>>>> the initial line calculation _dce_dsc_initial_line_calc(),
>>>> _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().
>>>
>>> The initial_line is already calculated in dpu_encoder.c. As for the
>>> _dce_dsc_ich_reset_override_needed(), I don't think we support partial
>>> updates in the upstream driver.
>>>
>>>>
>>>> All of these are again common between DSI and DP.
>>>>
>>>> So in addition to thinking about what can be moved to the drm_dsc_helper
>>>> also think about what is specific to MSM but common to DSI and DP modules.
>>>>
>>>> That was the bigger picture I was trying to convey.
>>>
>>
>> _dce_dsc_initial_line_calc which will get expanded with v1.2 gets added has much more than whats there in upstream today.
>>
>> Dumping everything in dpu_encoder is not the solution. Sorry.
> 
> But it is still the DPU thing. So, no problems.
> 

I am not fully convinced. We will wait for your post, then see how the 
code looks.

>>
>>>
>>>
> 

Re: [Intel-gfx] [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Jessica Zhang]

On 2/27/2023 1:24 PM, Abhinav Kumar wrote:
> 
> 
> On 2/27/2023 11:25 AM, Dmitry Baryshkov wrote:
>> 27 февраля 2023 г. 19:59:35 GMT+02:00, Abhinav Kumar 
>> <quic_abhinavk@quicinc.com> пишет:
>>>
>>>
>>> On 2/27/2023 4:45 AM, Dmitry Baryshkov wrote:
>>>> On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar 
>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
>>>>>> On 26/02/2023 02:47, Abhinav Kumar wrote:
>>>>>>> Hi Dmitry
>>>>>>>
>>>>>>> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>>>>>>>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>>>>>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar
>>>>>>>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>>>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>>>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar
>>>>>>>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>>>>>>>> Add DSC helper functions based on DSC configuration profiles
>>>>>>>>>>>>>>> to produce
>>>>>>>>>>>>>>> DSC related runtime parameters through both table look up 
>>>>>>>>>>>>>>> and
>>>>>>>>>>>>>>> runtime
>>>>>>>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> There are 6 different DSC configuration profiles are 
>>>>>>>>>>>>>>> supported
>>>>>>>>>>>>>>> currently.
>>>>>>>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC
>>>>>>>>>>>>>>> version (V1.1),
>>>>>>>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> These helpers should go to
>>>>>>>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>>>>>>>> Also please check that they can be used for i915 or for 
>>>>>>>>>>>>>> amdgpu
>>>>>>>>>>>>>> (ideally for both of them).
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> No, it cannot. So each DSC encoder parameter is calculated 
>>>>>>>>>>>>> based
>>>>>>>>>>>>> on the HW core which is being used.
>>>>>>>>>>>>>
>>>>>>>>>>>>> They all get packed to the same DSC structure which is the
>>>>>>>>>>>>> struct drm_dsc_config but the way the parameters are 
>>>>>>>>>>>>> computed is
>>>>>>>>>>>>> specific to the HW.
>>>>>>>>>>>>>
>>>>>>>>>>>>> This DPU file helper still uses the drm_dsc_helper's
>>>>>>>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but
>>>>>>>>>>>>> the parameters themselves are very HW specific and belong to
>>>>>>>>>>>>> each vendor's dir.
>>>>>>>>>>>>>
>>>>>>>>>>>>> This is not unique to MSM.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Lets take a few other examples:
>>>>>>>>>>>>>
>>>>>>>>>>>>> AMD:
>>>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> i915:
>>>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> I checked several values here. Intel driver defines more 
>>>>>>>>>>>> bpc/bpp
>>>>>>>>>>>> combinations, but the ones which are defined in intel_vdsc 
>>>>>>>>>>>> and in
>>>>>>>>>>>> this patch seem to match. If there are major differences there,
>>>>>>>>>>>> please point me to the exact case.
>>>>>>>>>>>>
>>>>>>>>>>>> I remember that AMD driver might have different values.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Some values in the rc_params table do match. But the
>>>>>>>>>>> rc_buf_thresh[] doesnt.
>>>>>>>>>>
>>>>>>>>>> Because later they do:
>>>>>>>>>>
>>>>>>>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Vs
>>>>>>>>>>>
>>>>>>>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>>>>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>>>>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>>>>>>>> +};
>>>>>>>>>>
>>>>>>>>>> I'd prefer to have 896, 1792, etc. here, as those values come 
>>>>>>>>>> from the
>>>>>>>>>> standard. As it's done in the Intel driver.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Got it, thanks
>>>>>>>>>
>>>>>>>>>>> I dont know the AMD calculation very well to say that moving 
>>>>>>>>>>> this
>>>>>>>>>>> to the
>>>>>>>>>>> helper is going to help.
>>>>>>>>>>
>>>>>>>>>> Those calculations correspond (more or less) at the first 
>>>>>>>>>> glance to
>>>>>>>>>> what intel does for their newer generations. I think that's 
>>>>>>>>>> not our
>>>>>>>>>> problem for now.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Well, we have to figure out if each value matches and if each of
>>>>>>>>> them come from the spec for us and i915 and from which section. So
>>>>>>>>> it is unfortunately our problem.
>>>>>>>>
>>>>>>>> Otherwise it will have to be handled by Marijn, me or anybody else
>>>>>>>> wanting to hack up the DSC code. Or by anybody adding DSC 
>>>>>>>> support to
>>>>>>>> the next platform and having to figure out the difference between
>>>>>>>> i915, msm and their platform.
>>>>>>>>
>>>>>>>
>>>>>>> Yes, I wonder why the same doubt didn't arise when the other vendors
>>>>>>> added their support both from other maintainers and others.
>>>>>>>
>>>>>>> Which makes me think that like I wrote in my previous response, 
>>>>>>> these
>>>>>>> are "recommended" values in the spec but its not mandatory.
>>>>>>
>>>>>> I think, it is because there were no other drivers to compare. In 
>>>>>> other
>>>>>> words, for a first driver it is pretty logical to have everything
>>>>>> handled on its own. As soon as we start getting other 
>>>>>> implementations of
>>>>>> a feature, it becomes logical to think if the code can be 
>>>>>> generalized.
>>>>>> This is what we see we with the HDCP series or with the code being 
>>>>>> moved
>>>>>> to DP helpers.
>>>>>>
>>>>>
>>>>> We were not the second, MSM was/is the third to add support for DSC 
>>>>> afer
>>>>> i915 and AMD. Thats what made me think why whoever was the second 
>>>>> didnt
>>>>> end up generalizing. Was it just missed out or was it intentionally 
>>>>> left
>>>>> in the vendor driver.
>>>>
>>>> I didn't count AMD here, since it calculates some of the params rather
>>>> than using the fixed ones from the model.
>>>>
>>>>>
>>>>>>>
>>>>>>> Moving this to the drm_dsc_helper is generalizing the tables and not
>>>>>>> giving room for the vendors to customize even if they want to (which
>>>>>>> the spec does allow).
>>>>>>
>>>>>> That depends on the API you select. For example, in
>>>>>> intel_dsc_compute_params() I see customization being applied to
>>>>>> rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
>>>>>>
>>>>>
>>>>> Thanks for going through the i915 to figure out that the 6bpp is 
>>>>> handled
>>>>> in a customized way. So what you are saying is let the helper first 
>>>>> fill
>>>>> up the recommended values of the spec, whatever is changed from 
>>>>> that let
>>>>> the vendor driver override that.
>>>>>
>>>>> Thats where the case-by-case handling comes.
>>>>>
>>>>> Why not we do this way? Like you mentioned lets move these tables 
>>>>> to the
>>>>> drm_dsc_helper and let MSM driver first use those.
>>>>>
>>>>> Then in a separate patchset if i915 and AMD would like to move to 
>>>>> that,
>>>>> let them handle it for their respective drivers instead of MSM going
>>>>> through whats customized for each calculation and doing it.
>>>>>
>>>>> I am hesitant to take up that effort.
>>>>
>>>> Writing a tool to convert model's rc_Nbpc_Mbpp_foo.cfg into C
>>>> languages structures used by Intel code took 15-20 minutes. Plugging
>>>> generated structures took another 5 minutes. I will send the patches
>>>> later today or tomorrow, as I find a time slot to clean them. Thank
>>>> you for spending more time on arguing than it took me to generate &
>>>> verify the data.
>>>>
>>>
>>> Great, we will wait for your patches. We didnt intend to spend time 
>>> on this at this point. We always wanted to take it up in a separate 
>>> series of moving the tables.
>>
>> Getting rid of msm_display_dsc_config and then making use of 
>> drm_dsc_compute_rc_parameters() was bad enough. So, let's get things 
>> done in a good way now, rather than at some random point later.
>>
> 
> Alright, we will wait for your change then :)
> 
>>
>>>
>>> You preferred not to wait. Upto you.
>>>
>>> So thanks for doing it.
>>>
>>>>>
>>>>> If the recommended values work for the vendor, they can clean it up 
>>>>> and
>>>>> move to the drm_dsc_helper themselves and preserving their
>>>>> customizations rather than one vendor doing it for all of them.
>>>>>
>>>>>> In case the driver needs to perform customization of the params, 
>>>>>> nothing
>>>>>> stops it drop applying after filling all the RC params in the
>>>>>> drm_dsc_config struct via the generic helper.
>>>>>>
>>>>>>
>>>>>>> So if this has any merit and if you or Marijn would like to take it
>>>>>>> up, go for it. We would do the same thing as either of you would 
>>>>>>> have
>>>>>>> to in terms of figuring out the difference between msm and the 
>>>>>>> i915 code.
>>>>>>>
>>>>>>> This is not a generic API we are trying to put in a helper, these 
>>>>>>> are
>>>>>>> hard-coded tables so there is a difference between looking at 
>>>>>>> these Vs
>>>>>>> looking at some common code which can move to the core.
>>>>>>>
>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Also, i think its too risky to change other drivers to use
>>>>>>>>>>> whatever math
>>>>>>>>>>> we put in the drm_dsc_helper to compute thr RC params because
>>>>>>>>>>> their code
>>>>>>>>>>> might be computing and using this tables differently.
>>>>>>>>>>>
>>>>>>>>>>> Its too much ownership for MSM developers to move this to
>>>>>>>>>>> drm_dsc_helper
>>>>>>>>>>> and own that as it might cause breakage of basic DSC even if 
>>>>>>>>>>> some
>>>>>>>>>>> values
>>>>>>>>>>> are repeated.
>>>>>>>>>>
>>>>>>>>>> It's time to stop thinking about ownership and start thinking 
>>>>>>>>>> about
>>>>>>>>>> shared code. We already have two instances of DSC tables. I don't
>>>>>>>>>> think having a third instance, which is a subset of an existing
>>>>>>>>>> dataset, would be beneficial to anybody.
>>>>>>>>>> AMD has complicated code which supports half-bit bpp and 
>>>>>>>>>> calculates
>>>>>>>>>> some of the parameters. But sharing data with the i915 driver is
>>>>>>>>>> straightforward.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Sorry, but I would like to get an ack from i915 folks if this 
>>>>>>>>> is going
>>>>>>>>> to be useful to them if we move this to helper because we have to
>>>>>>>>> look at every table. Not just one.
>>>>>>>>
>>>>>>>> Added i915 maintainers to the CC list for them to be able to 
>>>>>>>> answer.
>>>>>>>>
>>>>>>>
>>>>>>> Thanks, lets wait to hear from them about where finally these tables
>>>>>>> should go but thats can be taken up as a separate effort too.
>>>>>>>
>>>>>>>>>
>>>>>>>>> Also, this is just 1.1, we will add more tables for 1.2. So we 
>>>>>>>>> will
>>>>>>>>> have to end up changing both 1.1 and 1.2 tables as they are
>>>>>>>>> different for QC.
>>>>>>>>
>>>>>>>> I haven't heard back from Kuogee about the possible causes of using
>>>>>>>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on
>>>>>>>> that? In other words, can we always stick to the values from 1.2
>>>>>>>> standard? What will be the drawback?
>>>>>>>>
>>>>>>>> Otherwise, we'd have to have two different sets of values, like you
>>>>>>>> do in your vendor driver.
>>>>>>>>
>>>>>>>
>>>>>>> I have responded to this in the other email.
>>>>>>>
>>>>>>> All this being said, even if the rc tables move the drm_dsc_helper
>>>>>>> either now or later on, we will still need MSM specific calculations
>>>>>>> for many of the other encoder parameters (which are again either
>>>>>>> hard-coded or calculated). Please refer to the
>>>>>>> sde_dsc_populate_dsc_config() downstream. And yes, you will not find
>>>>>>> those in the DP spec directly.
>>>>>>>
>>>>>>> So we will still need a dsc helper for MSM calculations to be common
>>>>>>> for DSI / DP irrespective of where the tables go.
>>>>>>>
>>>>>>> So, lets finalize that first.
>>>>>>
>>>>>> I went on and trimmed sde_dsc_populate_dsc_config() to remove
>>>>>> duplication with the drm_dsc_compute_rc_parameters() (which we 
>>>>>> already
>>>>>> use for the MSM DSI DSC).
>>>>>>
>>>>>> Not much is left:
>>>>>>
>>>>>> dsc->first_line_bpg_offset set via the switch
>>>>>>
>>>>>> dsc->line_buf_depth = bpc + 1;
>>>>>> dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
>>>>>>            DSC_MUX_WORD_SIZE_8_10_BPC;
>>>>>>
>>>>>> if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
>>>>>>        dsc->nsl_bpg_offset = (2048 *
>>>>>>                 (DIV_ROUND_UP(dsc->second_line_bpg_offset,
>>>>>>                                    (dsc->slice_height - 1))));
>>>>>>
>>>>>> dsc->initial_scale_value = 8 * dsc->rc_model_size /
>>>>>>                            (dsc->rc_model_size - 
>>>>>> dsc->initial_offset);
>>>>>>
>>>>>>
>>>>>> mux_word_size comes from the standard (must)
>>>>>> initial_scale_value calculation is recommended, but not required
>>>>>> nsl_bpg_offset follows the standard (must), also see below (*).
>>>>>>
>>>>>> first_line_bpg_offset calculation differs between three drivers. The
>>>>>> standard also provides a recommended formulas. I think we can 
>>>>>> leave it
>>>>>> as is for now.
>>>>>>
>>>>>> I think, that mux_word_size and nsl_bpg_offset calculation should be
>>>>>> moved to drm_dsc_compute_rc_parameters(), while leaving
>>>>>> initial_scale_value in place (in the driver code).
>>>>>>
>>>>>> * I think nsl_bpg_offset is slightly incorrectly calculated. Standard
>>>>>> demands that it is set to 'second_line_bpg_offset / (slice_height 
>>>>>> - 1),
>>>>>> rounded up to 16 fraction bits', while SDE driver code sets it to the
>>>>>> value rounded up to the next integer (having 16 fraction bits
>>>>>> representation).
>>>>>>
>>>>>> In my opinion correct calculation should be:
>>>>>> dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * 
>>>>>> dsc->second_line_bpg_offset,
>>>>>>                                    (dsc->slice_height - 1));
>>>>>>
>>>>>> Could you please check, which one is correct according to the 
>>>>>> standard?
>>>>>>
>>>>>>
>>>>>
>>>>> Sure, i will check about nsl_bpg_offset. But sorry if I was not more
>>>>> clear about this but sde_dsc_populate_dsc_config() is only one example
>>>>> which from your analysis can be moved to the drm_dsc_helper() but not
>>>>> the initial line calculation _dce_dsc_initial_line_calc(),
>>>>> _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().
>>>>
>>>> The initial_line is already calculated in dpu_encoder.c. As for the
>>>> _dce_dsc_ich_reset_override_needed(), I don't think we support partial
>>>> updates in the upstream driver.
>>>>
>>>>>
>>>>> All of these are again common between DSI and DP.
>>>>>
>>>>> So in addition to thinking about what can be moved to the 
>>>>> drm_dsc_helper
>>>>> also think about what is specific to MSM but common to DSI and DP 
>>>>> modules.
>>>>>
>>>>> That was the bigger picture I was trying to convey.
>>>>
>>>
>>> _dce_dsc_initial_line_calc which will get expanded with v1.2 gets 
>>> added has much more than whats there in upstream today.
>>>
>>> Dumping everything in dpu_encoder is not the solution. Sorry.
>>
>> But it is still the DPU thing. So, no problems.
>>
> 
> I am not fully convinced. We will wait for your post, then see how the 
> code looks.

Hi Dmitry and Abhinav,

Just wanted to follow up on this thread. I've gone over the MSM-specific 
DSC params for DP and DSI and have found a few shared calculations and 
variables between both DSI and DP paths:

- (as mentioned earlier in the thread) almost all the calculations in 
dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The 
only difference in the math I'm seeing is initial_scale_value.

- dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were introduced 
in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU timing 
engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line 
(which is calculated differently between DP and DSI), but 
dce_bytes_per_line is calculated the same way between DP and DSI.

To avoid having to duplicate math in 2 different places, I think it 
would help to have these calculations in some msm_dsc_helper.c file. Any 
thoughts on this?

Thanks,

Jessica Zhang

[1] 
https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756

[2] https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1

> 
>>>
>>>>
>>>>
>>

Re: [Intel-gfx] [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Dmitry Baryshkov]

Hi,

[removed previous conversation]

>
> Hi Dmitry and Abhinav,
>
> Just wanted to follow up on this thread. I've gone over the MSM-specific
> DSC params for DP and DSI and have found a few shared calculations and
> variables between both DSI and DP paths:
>
> - (as mentioned earlier in the thread) almost all the calculations in
> dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The
> only difference in the math I'm seeing is initial_scale_value.

The value in dsi code is valid for initial_offset = 6144. Please use
the formula from the standard (= sde_dsc_populate_dsc_config) and add
it to drm_dsc_helper.c

If I remember correctly the last remaining item in
dsi_populate_dsc_params() (except mentioned initial_offset) was
line_buf_depth, see [3]. I'm not sure about setting it to bpc+1.
According to the standard it should come from a DSC decoder spec,
which means it should be set by the DSI panel driver or via
drm_dp_dsc_sink_line_buf_depth() in the case of DP output.

> - dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were introduced
> in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU timing
> engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line
> (which is calculated differently between DP and DSI), but
> dce_bytes_per_line is calculated the same way between DP and DSI.
>
> To avoid having to duplicate math in 2 different places, I think it
> would help to have these calculations in some msm_dsc_helper.c file. Any
> thoughts on this?

dsc_extra_pclk_cycle_cnt and dce_bytes_per_line are used only in DPU
code, so they can stay in DPU driver.

>
> Thanks,
>
> Jessica Zhang
>
> [1]
> https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756
>
> [2] https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1

[3] https://patchwork.freedesktop.org/patch/525441/?series=114472&rev=2



-- 
With best wishes
Dmitry

Re: [Intel-gfx] [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

On 3/16/2023 9:03 AM, Dmitry Baryshkov wrote:
> Hi,
> 
> [removed previous conversation]
> 
>>
>> Hi Dmitry and Abhinav,
>>
>> Just wanted to follow up on this thread. I've gone over the MSM-specific
>> DSC params for DP and DSI and have found a few shared calculations and
>> variables between both DSI and DP paths:
>>
>> - (as mentioned earlier in the thread) almost all the calculations in
>> dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The
>> only difference in the math I'm seeing is initial_scale_value.
> 
> The value in dsi code is valid for initial_offset = 6144. Please use
> the formula from the standard (= sde_dsc_populate_dsc_config) and add
> it to drm_dsc_helper.c
> 
> If I remember correctly the last remaining item in
> dsi_populate_dsc_params() (except mentioned initial_offset) was
> line_buf_depth, see [3]. I'm not sure about setting it to bpc+1.
> According to the standard it should come from a DSC decoder spec,
> which means it should be set by the DSI panel driver or via
> drm_dp_dsc_sink_line_buf_depth() in the case of DP output.
> 
>> - dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were introduced
>> in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU timing
>> engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line
>> (which is calculated differently between DP and DSI), but
>> dce_bytes_per_line is calculated the same way between DP and DSI.
>>
>> To avoid having to duplicate math in 2 different places, I think it
>> would help to have these calculations in some msm_dsc_helper.c file. Any
>> thoughts on this?
> 
> dsc_extra_pclk_cycle_cnt and dce_bytes_per_line are used only in DPU
> code, so they can stay in DPU driver.
> 

They can stay in the dpu driver is fine but where?

Like Jessica wrote, this is computed and used in 3 places today :

1) DSI video engine computation
2) DP controller computation
3) timing engine programming

So either we have a helper in a common location somewhere so that these 
3 modules can call that helper and use it OR each module duplicates the 
computation code.

What should be the common location is the discussion here.

It cannot be dpu_encoder.c as the DSI/DP dont call into the encoder methods.

>>
>> Thanks,
>>
>> Jessica Zhang
>>
>> [1]
>> https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756
>>
>> [2] https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1
> 
> [3] https://patchwork.freedesktop.org/patch/525441/?series=114472&rev=2
> 
> 
> 

Re: [Intel-gfx] [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Dmitry Baryshkov]

On 16/03/2023 18:13, Abhinav Kumar wrote:
> 
> 
> On 3/16/2023 9:03 AM, Dmitry Baryshkov wrote:
>> Hi,
>>
>> [removed previous conversation]
>>
>>>
>>> Hi Dmitry and Abhinav,
>>>
>>> Just wanted to follow up on this thread. I've gone over the MSM-specific
>>> DSC params for DP and DSI and have found a few shared calculations and
>>> variables between both DSI and DP paths:
>>>
>>> - (as mentioned earlier in the thread) almost all the calculations in
>>> dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The
>>> only difference in the math I'm seeing is initial_scale_value.
>>
>> The value in dsi code is valid for initial_offset = 6144. Please use
>> the formula from the standard (= sde_dsc_populate_dsc_config) and add
>> it to drm_dsc_helper.c
>>
>> If I remember correctly the last remaining item in
>> dsi_populate_dsc_params() (except mentioned initial_offset) was
>> line_buf_depth, see [3]. I'm not sure about setting it to bpc+1.
>> According to the standard it should come from a DSC decoder spec,
>> which means it should be set by the DSI panel driver or via
>> drm_dp_dsc_sink_line_buf_depth() in the case of DP output.
>>
>>> - dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were introduced
>>> in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU timing
>>> engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line
>>> (which is calculated differently between DP and DSI), but
>>> dce_bytes_per_line is calculated the same way between DP and DSI.
>>>
>>> To avoid having to duplicate math in 2 different places, I think it
>>> would help to have these calculations in some msm_dsc_helper.c file. Any
>>> thoughts on this?
>>
>> dsc_extra_pclk_cycle_cnt and dce_bytes_per_line are used only in DPU
>> code, so they can stay in DPU driver.
>>
> 
> They can stay in the dpu driver is fine but where?
> 
> Like Jessica wrote, this is computed and used in 3 places today :
> 
> 1) DSI video engine computation
> 2) DP controller computation
> 3) timing engine programming

Please excuse me if I'm wrong. I checked both vendor techpack and the 
Kuogee's patches. I see them being used only in the SDE / DPU driver 
code. Could you please point me to the code path that we are discussing?


> So either we have a helper in a common location somewhere so that these 
> 3 modules can call that helper and use it OR each module duplicates the 
> computation code.
> 
> What should be the common location is the discussion here.
> 
> It cannot be dpu_encoder.c as the DSI/DP dont call into the encoder 
> methods.
> 
>>>
>>> Thanks,
>>>
>>> Jessica Zhang
>>>
>>> [1]
>>> https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756
>>>
>>> [2] https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1
>>
>> [3] https://patchwork.freedesktop.org/patch/525441/?series=114472&rev=2
>>
>>
>>

-- 
With best wishes
Dmitry

Re: [Intel-gfx] [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

On 3/16/2023 9:23 AM, Dmitry Baryshkov wrote:
> On 16/03/2023 18:13, Abhinav Kumar wrote:
>>
>>
>> On 3/16/2023 9:03 AM, Dmitry Baryshkov wrote:
>>> Hi,
>>>
>>> [removed previous conversation]
>>>
>>>>
>>>> Hi Dmitry and Abhinav,
>>>>
>>>> Just wanted to follow up on this thread. I've gone over the 
>>>> MSM-specific
>>>> DSC params for DP and DSI and have found a few shared calculations and
>>>> variables between both DSI and DP paths:
>>>>
>>>> - (as mentioned earlier in the thread) almost all the calculations in
>>>> dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The
>>>> only difference in the math I'm seeing is initial_scale_value.
>>>
>>> The value in dsi code is valid for initial_offset = 6144. Please use
>>> the formula from the standard (= sde_dsc_populate_dsc_config) and add
>>> it to drm_dsc_helper.c
>>>
>>> If I remember correctly the last remaining item in
>>> dsi_populate_dsc_params() (except mentioned initial_offset) was
>>> line_buf_depth, see [3]. I'm not sure about setting it to bpc+1.
>>> According to the standard it should come from a DSC decoder spec,
>>> which means it should be set by the DSI panel driver or via
>>> drm_dp_dsc_sink_line_buf_depth() in the case of DP output.
>>>
>>>> - dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were 
>>>> introduced
>>>> in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU timing
>>>> engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line
>>>> (which is calculated differently between DP and DSI), but
>>>> dce_bytes_per_line is calculated the same way between DP and DSI.
>>>>
>>>> To avoid having to duplicate math in 2 different places, I think it
>>>> would help to have these calculations in some msm_dsc_helper.c file. 
>>>> Any
>>>> thoughts on this?
>>>
>>> dsc_extra_pclk_cycle_cnt and dce_bytes_per_line are used only in DPU
>>> code, so they can stay in DPU driver.
>>>
>>
>> They can stay in the dpu driver is fine but where?
>>
>> Like Jessica wrote, this is computed and used in 3 places today :
>>
>> 1) DSI video engine computation
>> 2) DP controller computation
>> 3) timing engine programming
> 
> Please excuse me if I'm wrong. I checked both vendor techpack and the 
> Kuogee's patches. I see them being used only in the SDE / DPU driver 
> code. Could you please point me to the code path that we are discussing?
> 

DSI code :

https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/msm/dsi/dsi_host.c#L868

DP code:

Refer to dp_panel_dsc_pclk_param_calc in 
https://patchwork.freedesktop.org/patch/519837/?series=113240&rev=1

Timing engine:

refer to https://patchwork.freedesktop.org/patch/519838/?series=113240&rev=1

Probably confusion is due to the naming. bytes_per_line is nothing but 
bytes_per_pkt * pkt_per_line but the concept is common for DP and DSI.

+		if (phys->comp_type == MSM_DISPLAY_COMPRESSION_DSC) {
+			phys->dsc_extra_pclk_cycle_cnt = dsc_info->pclk_per_line;
+			phys->dsc_extra_disp_width = dsc_info->extra_width;
+			phys->dce_bytes_per_line =
+				dsc_info->bytes_per_pkt * dsc_info->pkt_per_line;

> 
>> So either we have a helper in a common location somewhere so that 
>> these 3 modules can call that helper and use it OR each module 
>> duplicates the computation code.
>>
>> What should be the common location is the discussion here.
>>
>> It cannot be dpu_encoder.c as the DSI/DP dont call into the encoder 
>> methods.
>>
>>>>
>>>> Thanks,
>>>>
>>>> Jessica Zhang
>>>>
>>>> [1]
>>>> https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756 
>>>>
>>>>
>>>> [2] https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1
>>>
>>> [3] https://patchwork.freedesktop.org/patch/525441/?series=114472&rev=2
>>>
>>>
>>>
> 

Re: [Intel-gfx] [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Abhinav Kumar]

On 3/16/2023 9:36 AM, Abhinav Kumar wrote:
> 
> 
> On 3/16/2023 9:23 AM, Dmitry Baryshkov wrote:
>> On 16/03/2023 18:13, Abhinav Kumar wrote:
>>>
>>>
>>> On 3/16/2023 9:03 AM, Dmitry Baryshkov wrote:
>>>> Hi,
>>>>
>>>> [removed previous conversation]
>>>>
>>>>>
>>>>> Hi Dmitry and Abhinav,
>>>>>
>>>>> Just wanted to follow up on this thread. I've gone over the 
>>>>> MSM-specific
>>>>> DSC params for DP and DSI and have found a few shared calculations and
>>>>> variables between both DSI and DP paths:
>>>>>
>>>>> - (as mentioned earlier in the thread) almost all the calculations in
>>>>> dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The
>>>>> only difference in the math I'm seeing is initial_scale_value.
>>>>
>>>> The value in dsi code is valid for initial_offset = 6144. Please use
>>>> the formula from the standard (= sde_dsc_populate_dsc_config) and add
>>>> it to drm_dsc_helper.c
>>>>

Yes, I agree with this part. for rc_model_size we can use 
DSC_RC_MODEL_SIZE_CONST.

initial_offset is already handled in 
https://patchwork.freedesktop.org/patch/525424/?series=114472&rev=2

Then we can use this math:

rc_model_size / (rc_model_size -
initial_offset), keeping in mind that initial_scale_value has three 
fractional bits.

So this would be 8192 / (8192 - 6144) = 4

Then << 3 for 3 fractional bits = 32.

>>>> If I remember correctly the last remaining item in
>>>> dsi_populate_dsc_params() (except mentioned initial_offset) was
>>>> line_buf_depth, see [3]. I'm not sure about setting it to bpc+1.
>>>> According to the standard it should come from a DSC decoder spec,
>>>> which means it should be set by the DSI panel driver or via
>>>> drm_dp_dsc_sink_line_buf_depth() in the case of DP output.
>>>>
>>>>> - dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were 
>>>>> introduced
>>>>> in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU 
>>>>> timing
>>>>> engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line
>>>>> (which is calculated differently between DP and DSI), but
>>>>> dce_bytes_per_line is calculated the same way between DP and DSI.
>>>>>
>>>>> To avoid having to duplicate math in 2 different places, I think it
>>>>> would help to have these calculations in some msm_dsc_helper.c 
>>>>> file. Any
>>>>> thoughts on this?
>>>>
>>>> dsc_extra_pclk_cycle_cnt and dce_bytes_per_line are used only in DPU
>>>> code, so they can stay in DPU driver.
>>>>
>>>
>>> They can stay in the dpu driver is fine but where?
>>>
>>> Like Jessica wrote, this is computed and used in 3 places today :
>>>
>>> 1) DSI video engine computation
>>> 2) DP controller computation
>>> 3) timing engine programming
>>
>> Please excuse me if I'm wrong. I checked both vendor techpack and the 
>> Kuogee's patches. I see them being used only in the SDE / DPU driver 
>> code. Could you please point me to the code path that we are discussing?
>>
> 
> DSI code :
> 
> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/msm/dsi/dsi_host.c#L868 
> 
> 
> DP code:
> 
> Refer to dp_panel_dsc_pclk_param_calc in 
> https://patchwork.freedesktop.org/patch/519837/?series=113240&rev=1
> 
> Timing engine:
> 
> refer to 
> https://patchwork.freedesktop.org/patch/519838/?series=113240&rev=1
> 
> Probably confusion is due to the naming. bytes_per_line is nothing but 
> bytes_per_pkt * pkt_per_line but the concept is common for DP and DSI.
> 
> +        if (phys->comp_type == MSM_DISPLAY_COMPRESSION_DSC) {
> +            phys->dsc_extra_pclk_cycle_cnt = dsc_info->pclk_per_line;
> +            phys->dsc_extra_disp_width = dsc_info->extra_width;
> +            phys->dce_bytes_per_line =
> +                dsc_info->bytes_per_pkt * dsc_info->pkt_per_line;
> 
>>
>>> So either we have a helper in a common location somewhere so that 
>>> these 3 modules can call that helper and use it OR each module 
>>> duplicates the computation code.
>>>
>>> What should be the common location is the discussion here.
>>>
>>> It cannot be dpu_encoder.c as the DSI/DP dont call into the encoder 
>>> methods.
>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Jessica Zhang
>>>>>
>>>>> [1]
>>>>> https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756 
>>>>>
>>>>>
>>>>> [2] 
>>>>> https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1
>>>>
>>>> [3] https://patchwork.freedesktop.org/patch/525441/?series=114472&rev=2
>>>>
>>>>
>>>>
>>

Re: [Intel-gfx] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

[Jani Nikula]

On Sun, 26 Feb 2023, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
> On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote:
>> On 26/02/2023 02:47, Abhinav Kumar wrote:
>>> Hi Dmitry
>>>
>>> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote:
>>>> On 25/02/2023 02:36, Abhinav Kumar wrote:
>>>>>
>>>>>
>>>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote:
>>>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar 
>>>>>> <quic_abhinavk@quicinc.com> wrote:
>>>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote:
>>>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar 
>>>>>>>> <quic_abhinavk@quicinc.com> пишет:
>>>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote:
>>>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote:
>>>>>>>>>>> Add DSC helper functions based on DSC configuration profiles 
>>>>>>>>>>> to produce
>>>>>>>>>>> DSC related runtime parameters through both table look up and 
>>>>>>>>>>> runtime
>>>>>>>>>>> calculation to support DSC on DPU.
>>>>>>>>>>>
>>>>>>>>>>> There are 6 different DSC configuration profiles are supported 
>>>>>>>>>>> currently.
>>>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC 
>>>>>>>>>>> version (V1.1),
>>>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10),
>>>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1).
>>>>>>>>>>>
>>>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later.
>>>>>>>>>>
>>>>>>>>>> These helpers should go to 
>>>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c
>>>>>>>>>> Also please check that they can be used for i915 or for amdgpu 
>>>>>>>>>> (ideally for both of them).
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based 
>>>>>>>>> on the HW core which is being used.
>>>>>>>>>
>>>>>>>>> They all get packed to the same DSC structure which is the 
>>>>>>>>> struct drm_dsc_config but the way the parameters are computed is 
>>>>>>>>> specific to the HW.
>>>>>>>>>
>>>>>>>>> This DPU file helper still uses the drm_dsc_helper's 
>>>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but 
>>>>>>>>> the parameters themselves are very HW specific and belong to 
>>>>>>>>> each vendor's dir.
>>>>>>>>>
>>>>>>>>> This is not unique to MSM.
>>>>>>>>>
>>>>>>>>> Lets take a few other examples:
>>>>>>>>>
>>>>>>>>> AMD: 
>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165 
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> i915: 
>>>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379 
>>>>>>>>>
>>>>>>>>
>>>>>>>> I checked several values here. Intel driver defines more bpc/bpp 
>>>>>>>> combinations, but the ones which are defined in intel_vdsc and in 
>>>>>>>> this patch seem to match. If there are major differences there, 
>>>>>>>> please point me to the exact case.
>>>>>>>>
>>>>>>>> I remember that AMD driver might have different values.
>>>>>>>>
>>>>>>>
>>>>>>> Some values in the rc_params table do match. But the 
>>>>>>> rc_buf_thresh[] doesnt.
>>>>>>
>>>>>> Because later they do:
>>>>>>
>>>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6;
>>>>>>
>>>>>>>
>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40 
>>>>>>>
>>>>>>>
>>>>>>> Vs
>>>>>>>
>>>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = {
>>>>>>> +               0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54,
>>>>>>> +               0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e
>>>>>>> +};
>>>>>>
>>>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the
>>>>>> standard. As it's done in the Intel driver.
>>>>>>
>>>>>
>>>>> Got it, thanks
>>>>>
>>>>>>> I dont know the AMD calculation very well to say that moving this 
>>>>>>> to the
>>>>>>> helper is going to help.
>>>>>>
>>>>>> Those calculations correspond (more or less) at the first glance to
>>>>>> what intel does for their newer generations. I think that's not our
>>>>>> problem for now.
>>>>>>
>>>>>
>>>>> Well, we have to figure out if each value matches and if each of 
>>>>> them come from the spec for us and i915 and from which section. So 
>>>>> it is unfortunately our problem.
>>>>
>>>> Otherwise it will have to be handled by Marijn, me or anybody else 
>>>> wanting to hack up the DSC code. Or by anybody adding DSC support to 
>>>> the next platform and having to figure out the difference between 
>>>> i915, msm and their platform.
>>>>
>>>
>>> Yes, I wonder why the same doubt didn't arise when the other vendors 
>>> added their support both from other maintainers and others.
>>>
>>> Which makes me think that like I wrote in my previous response, these 
>>> are "recommended" values in the spec but its not mandatory.
>> 
>> I think, it is because there were no other drivers to compare. In other 
>> words, for a first driver it is pretty logical to have everything 
>> handled on its own. As soon as we start getting other implementations of 
>> a feature, it becomes logical to think if the code can be generalized. 
>> This is what we see we with the HDCP series or with the code being moved 
>> to DP helpers.
>> 
>
> We were not the second, MSM was/is the third to add support for DSC afer 
> i915 and AMD. Thats what made me think why whoever was the second didnt 
> end up generalizing. Was it just missed out or was it intentionally left 
> in the vendor driver.
>
>>>
>>> Moving this to the drm_dsc_helper is generalizing the tables and not 
>>> giving room for the vendors to customize even if they want to (which 
>>> the spec does allow).
>> 
>> That depends on the API you select. For example, in 
>> intel_dsc_compute_params() I see customization being applied to 
>> rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver.
>> 
>
> Thanks for going through the i915 to figure out that the 6bpp is handled 
> in a customized way. So what you are saying is let the helper first fill 
> up the recommended values of the spec, whatever is changed from that let 
> the vendor driver override that.
>
> Thats where the case-by-case handling comes.
>
> Why not we do this way? Like you mentioned lets move these tables to the 
> drm_dsc_helper and let MSM driver first use those.
>
> Then in a separate patchset if i915 and AMD would like to move to that, 
> let them handle it for their respective drivers instead of MSM going 
> through whats customized for each calculation and doing it.
>
> I am hesitant to take up that effort.
>
> If the recommended values work for the vendor, they can clean it up and 
> move to the drm_dsc_helper themselves and preserving their 
> customizations rather than one vendor doing it for all of them.

I think the thing to do is to define *interfaces* for accessing the
various parameters in a reasonable manner.

Even in your code, it'll be helpful for any future conversion to shared
arrays to not access the local arrays directly.

If this gets added to kms helpers, with the spec values verbatim and
reasonable interfaces, i915 will happily convert to using them.

BR,
Jani.



>
>> In case the driver needs to perform customization of the params, nothing 
>> stops it drop applying after filling all the RC params in the 
>> drm_dsc_config struct via the generic helper.
>> 
>> 
>>> So if this has any merit and if you or Marijn would like to take it 
>>> up, go for it. We would do the same thing as either of you would have 
>>> to in terms of figuring out the difference between msm and the i915 code.
>>>
>>> This is not a generic API we are trying to put in a helper, these are 
>>> hard-coded tables so there is a difference between looking at these Vs 
>>> looking at some common code which can move to the core.
>>>
>>>>>
>>>>>>>
>>>>>>> Also, i think its too risky to change other drivers to use 
>>>>>>> whatever math
>>>>>>> we put in the drm_dsc_helper to compute thr RC params because 
>>>>>>> their code
>>>>>>> might be computing and using this tables differently.
>>>>>>>
>>>>>>> Its too much ownership for MSM developers to move this to 
>>>>>>> drm_dsc_helper
>>>>>>> and own that as it might cause breakage of basic DSC even if some 
>>>>>>> values
>>>>>>> are repeated.
>>>>>>
>>>>>> It's time to stop thinking about ownership and start thinking about
>>>>>> shared code. We already have two instances of DSC tables. I don't
>>>>>> think having a third instance, which is a subset of an existing
>>>>>> dataset, would be beneficial to anybody.
>>>>>> AMD has complicated code which supports half-bit bpp and calculates
>>>>>> some of the parameters. But sharing data with the i915 driver is
>>>>>> straightforward.
>>>>>>
>>>>>
>>>>> Sorry, but I would like to get an ack from i915 folks if this is going
>>>>> to be useful to them if we move this to helper because we have to 
>>>>> look at every table. Not just one.
>>>>
>>>> Added i915 maintainers to the CC list for them to be able to answer.
>>>>
>>>
>>> Thanks, lets wait to hear from them about where finally these tables 
>>> should go but thats can be taken up as a separate effort too.
>>>
>>>>>
>>>>> Also, this is just 1.1, we will add more tables for 1.2. So we will 
>>>>> have to end up changing both 1.1 and 1.2 tables as they are 
>>>>> different for QC.
>>>>
>>>> I haven't heard back from Kuogee about the possible causes of using 
>>>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on 
>>>> that? In other words, can we always stick to the values from 1.2 
>>>> standard? What will be the drawback?
>>>>
>>>> Otherwise, we'd have to have two different sets of values, like you 
>>>> do in your vendor driver.
>>>>
>>>
>>> I have responded to this in the other email.
>>>
>>> All this being said, even if the rc tables move the drm_dsc_helper 
>>> either now or later on, we will still need MSM specific calculations 
>>> for many of the other encoder parameters (which are again either 
>>> hard-coded or calculated). Please refer to the 
>>> sde_dsc_populate_dsc_config() downstream. And yes, you will not find 
>>> those in the DP spec directly.
>>>
>>> So we will still need a dsc helper for MSM calculations to be common 
>>> for DSI / DP irrespective of where the tables go.
>>>
>>> So, lets finalize that first.
>> 
>> I went on and trimmed sde_dsc_populate_dsc_config() to remove 
>> duplication with the drm_dsc_compute_rc_parameters() (which we already 
>> use for the MSM DSI DSC).
>> 
>> Not much is left:
>> 
>> dsc->first_line_bpg_offset set via the switch
>> 
>> dsc->line_buf_depth = bpc + 1;
>> dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC:
>>          DSC_MUX_WORD_SIZE_8_10_BPC;
>> 
>> if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420))
>>      dsc->nsl_bpg_offset = (2048 *
>>               (DIV_ROUND_UP(dsc->second_line_bpg_offset,
>>                                  (dsc->slice_height - 1))));
>> 
>> dsc->initial_scale_value = 8 * dsc->rc_model_size /
>>                          (dsc->rc_model_size - dsc->initial_offset);
>> 
>> 
>> mux_word_size comes from the standard (must)
>> initial_scale_value calculation is recommended, but not required
>> nsl_bpg_offset follows the standard (must), also see below (*).
>> 
>> first_line_bpg_offset calculation differs between three drivers. The 
>> standard also provides a recommended formulas. I think we can leave it 
>> as is for now.
>> 
>> I think, that mux_word_size and nsl_bpg_offset calculation should be 
>> moved to drm_dsc_compute_rc_parameters(), while leaving 
>> initial_scale_value in place (in the driver code).
>> 
>> * I think nsl_bpg_offset is slightly incorrectly calculated. Standard 
>> demands that it is set to 'second_line_bpg_offset / (slice_height - 1), 
>> rounded up to 16 fraction bits', while SDE driver code sets it to the 
>> value rounded up to the next integer (having 16 fraction bits 
>> representation).
>> 
>> In my opinion correct calculation should be:
>> dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset,
>>                                  (dsc->slice_height - 1));
>> 
>> Could you please check, which one is correct according to the standard?
>> 
>> 
>
> Sure, i will check about nsl_bpg_offset. But sorry if I was not more 
> clear about this but sde_dsc_populate_dsc_config() is only one example 
> which from your analysis can be moved to the drm_dsc_helper() but not 
> the initial line calculation _dce_dsc_initial_line_calc(), 
> _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper().
>
> All of these are again common between DSI and DP.
>
> So in addition to thinking about what can be moved to the drm_dsc_helper 
> also think about what is specific to MSM but common to DSI and DP modules.
>
> That was the bigger picture I was trying to convey.

-- 
Jani Nikula, Intel Open Source Graphics Center