Re: [PATCH v2 06/50] drm/msm/dpu: correct sm8550 scaler

[Abhinav Kumar <quic_abhinavk@quicinc.com>]

Hi Dmitry

On 2/25/2023 3:06 PM, Dmitry Baryshkov wrote:
> On 24/02/2023 22:51, Abhinav Kumar wrote:
>>
>>
>> On 2/13/2023 9:36 AM, neil.armstrong@linaro.org wrote:
>>> On 13/02/2023 12:16, Dmitry Baryshkov wrote:
>>>> On 13/02/2023 12:41, Neil Armstrong wrote:
>>>>> On 12/02/2023 00:12, Dmitry Baryshkov wrote:
>>>>>> QSEED4 is a newer variant of QSEED3LITE, which should be used on
>>>>>> sm8550. Fix the DPU caps structure and used feature masks.
>>>>>
>>>>> I found nowhere SM8550 uses Qseed4, on downstream DT, it's written:
>>>>>          qcom,sde-qseed-sw-lib-rev = "qseedv3lite";
>>>>>          qcom,sde-qseed-scalar-version = <0x3002>;
>>>>
>>>> And then the techpack tells us starting from 0x3000 the v3lite is v4:
>>>>
>>>> https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/display-kernel.lnx.5.10.r8-rel/msm/sde/sde_hw_util.c#L59 
>>>>
>>>>
>>>> https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/display-kernel.lnx.5.10.r8-rel/msm/sde/sde_hw_util.c#L102 
>>>>
>>>
>>> OK then:
>>>
>>> Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
>>>
>>>>
>>
>> This little bit of confusion is because with downstream, the qseed is 
>> a separate usermode library having its own revision. So the SW lib 
>> version in this case is not exactly correlating with the scalar HW 
>> revision.
> 
> Can you possibly spend some more words here? I see that sde_hw_utils.c 
> programs scalers slightly different depending on the version of the 
> scaler. At some point the SDE driver was reading the register to 
> determine the revision. Then it switched to the revision specified in 
> the DTS (which, as far as I understand, corresponds to the HW register 
> contents).
> 
> So, where does SW revision come into the play? (and which library are we 
> talking about?). Is the 'v3lite' an SW revision? Or is the 0x3002 an SW 
> revision?
> 

qcom,sde-qseed-sw-lib-rev is the SW library revision for libscale.

This is a proprietary library used to calculate the LUTs for the qseed 
block. Its not used in the upstream version of the driver.

For upstream driver, the driver uses default settings for the LUTs which 
work for most of the common use-cases we see.

You can refer the below property names, there are programmed by the lib 
for the downstream driver.

3733 		msm_property_install_range(
3734 				&psde->property_info, "scaler_v2",
3735 				0x0, 0, ~0, 0, PLANE_PROP_SCALER_V2);
3736 		msm_property_install_blob(&psde->property_info,
3737 				"lut_sep", 0,
3738 				PLANE_PROP_SCALER_LUT_SEP);

No, 0x3002 is the HW revision of the qseed and thats why this change is 
correct because the SW library name/rev doesnt exactly match the qseed 
HW revision as its possible that even qseed3lite library can support the 
QSEED4 HW.

So we should be going off qcom,sde-qseed-scalar-version and not 
qcom,sde-qseed-sw-lib-rev.

>>
>> Since upstream DPU only cares about the HW revision of the scaler, we 
>> should be going off the qcom,sde-qseed-scalar-version.
>>
>> This change LGTM,
>>
>> Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
> 
>