Re: [PATCH v5 4/7] drm/msm: adreno: find bandwidth index of OPP and set it along freq index

[neil.armstrong@linaro.org]

On 16/12/2024 11:40, Akhil P Oommen wrote:
> On 12/16/2024 3:13 PM, neil.armstrong@linaro.org wrote:
>> On 14/12/2024 00:46, Konrad Dybcio wrote:
>>> On 13.12.2024 5:55 PM, Akhil P Oommen wrote:
>>>> On 12/13/2024 10:10 PM, neil.armstrong@linaro.org wrote:
>>>>> On 13/12/2024 17:31, Konrad Dybcio wrote:
>>>>>> On 13.12.2024 5:28 PM, neil.armstrong@linaro.org wrote:
>>>>>>> On 13/12/2024 16:37, Konrad Dybcio wrote:
>>>>>>>> On 13.12.2024 2:12 PM, Akhil P Oommen wrote:
>>>>>>>>> On 12/13/2024 3:07 AM, Neil Armstrong wrote:
>>>>>>>>>> On 12/12/2024 21:21, Konrad Dybcio wrote:
>>>>>>>>>>> On 11.12.2024 9:29 AM, Neil Armstrong wrote:
>>>>>>>>>>>> The Adreno GPU Management Unit (GMU) can also scale the DDR
>>>>>>>>>>>> Bandwidth
>>>>>>>>>>>> along the Frequency and Power Domain level, until now we left
>>>>>>>>>>>> the OPP
>>>>>>>>>>>> core scale the OPP bandwidth via the interconnect path.
>>>>>>>>>>>>
>>>>>>>>>>>> In order to enable bandwidth voting via the GPU Management
>>>>>>>>>>>> Unit (GMU), when an opp is set by devfreq we also look for
>>>>>>>>>>>> the corresponding bandwidth index in the previously generated
>>>>>>>>>>>> bw_table and pass this value along the frequency index to the
>>>>>>>>>>>> GMU.
>>>>>>>>>>>>
>>>>>>>>>>>> The GMU also takes another vote called AB which is a 16bit
>>>>>>>>>>>> quantized
>>>>>>>>>>>> value of the floor bandwidth against the maximum supported
>>>>>>>>>>>> bandwidth.
>>>>>>>>>>>>
>>>>>>>>>>>> The AB is calculated with a default 25% of the bandwidth like
>>>>>>>>>>>> the
>>>>>>>>>>>> downstream implementation too inform the GMU firmware the
>>>>>>>>>>>> minimal
>>>>>>>>>>>> quantity of bandwidth we require for this OPP.
>>>>>>>>>>>>
>>>>>>>>>>>> Since we now vote for all resources via the GMU, setting the OPP
>>>>>>>>>>>> is no more needed, so we can completely skip calling
>>>>>>>>>>>> dev_pm_opp_set_opp() in this situation.
>>>>>>>>>>>>
>>>>>>>>>>>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>>>>>>>>>>>> Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
>>>>>>>>>>>> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
>>>>>>>>>>>> ---
>>>>>>>>>>>>       drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 39 +++++++++++++
>>>>>>>>>>>> ++++
>>>>>>>>>>>> +++++++
>>>>>>>>>>>> +++++++++--
>>>>>>>>>>>>       drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  2 +-
>>>>>>>>>>>>       drivers/gpu/drm/msm/adreno/a6xx_hfi.c |  6 +++---
>>>>>>>>>>>>       drivers/gpu/drm/msm/adreno/a6xx_hfi.h |  5 +++++
>>>>>>>>>>>>       4 files changed, 46 insertions(+), 6 deletions(-)
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/
>>>>>>>>>>>> gpu/drm/
>>>>>>>>>>>> msm/adreno/a6xx_gmu.c
>>>>>>>>>>>> index
>>>>>>>>>>>> 36696d372a42a27b26a018b19e73bc6d8a4a5235..46ae0ec7a16a41d55755ce04fb32404cdba087be 100644
>>>>>>>>>>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>>>>>>>>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
>>>>>>>>>>>> @@ -110,9 +110,11 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu,
>>>>>>>>>>>> struct dev_pm_opp *opp,
>>>>>>>>>>>>                      bool suspended)
>>>>>>>>>>>>       {
>>>>>>>>>>>>           struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>>>>>>>>>>>> +    const struct a6xx_info *info = adreno_gpu->info->a6xx;
>>>>>>>>>>>>           struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
>>>>>>>>>>>>           struct a6xx_gmu *gmu = &a6xx_gpu->gmu;
>>>>>>>>>>>>           u32 perf_index;
>>>>>>>>>>>> +    u32 bw_index = 0;
>>>>>>>>>>>>           unsigned long gpu_freq;
>>>>>>>>>>>>           int ret = 0;
>>>>>>>>>>>>       @@ -125,6 +127,37 @@ void a6xx_gmu_set_freq(struct msm_gpu
>>>>>>>>>>>> *gpu,
>>>>>>>>>>>> struct dev_pm_opp *opp,
>>>>>>>>>>>>               if (gpu_freq == gmu->gpu_freqs[perf_index])
>>>>>>>>>>>>                   break;
>>>>>>>>>>>>       +    /* If enabled, find the corresponding DDR bandwidth
>>>>>>>>>>>> index */
>>>>>>>>>>>> +    if (info->bcms && gmu->nr_gpu_bws > 1) {
>>>>>>>>>>>
>>>>>>>>>>> if (gmu->nr_gpu_bws)
>>>>>>>>>>
>>>>>>>>>> gmu->nr_gpu_bws == 1 means there's not BW in the OPPs (index 0
>>>>>>>>>> is the
>>>>>>>>>> "off" state)
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> +        unsigned int bw = dev_pm_opp_get_bw(opp, true, 0);
>>>>>>>>>>>> +
>>>>>>>>>>>> +        for (bw_index = 0; bw_index < gmu->nr_gpu_bws - 1;
>>>>>>>>>>>> bw_index+
>>>>>>>>>>>> +) {
>>>>>>>>>>>> +            if (bw == gmu->gpu_bw_table[bw_index])
>>>>>>>>>>>> +                break;
>>>>>>>>>>>> +        }
>>>>>>>>>>>> +
>>>>>>>>>>>> +        /* Vote AB as a fraction of the max bandwidth */
>>>>>>>>>>>> +        if (bw) {
>>>>>>>>>>>
>>>>>>>>>>> This seems to only be introduced with certain a7xx too.. you
>>>>>>>>>>> should
>>>>>>>>>>> ping the GMU with HFI_VALUE_GMU_AB_VOTE to check if it's
>>>>>>>>>>> supported
>>>>>>>>>>
>>>>>>>>>> Good point
>>>>>>>>>
>>>>>>>>> No no. Doing this will trigger some assert in pre-A750 gmu
>>>>>>>>> firmwares. We
>>>>>>>>> learned it the hard way. No improvisation please. :)
>>>>>>>>
>>>>>>>> We shouldn't be sending that AB data to firmware that doesn't expect
>>>>>>>> it either too, though..
>>>>>>>
>>>>>>> Well we don't !
>>>>>>
>>>>>> The code in the scope that I quoted above does that
>>>>>
>>>>> No it doesn't, if the proper bcms are not declared in the gpu_info, it
>>>>> won't
>>>>
>>>> I think what Konrad meant was that IB voting is supported from a650+,
>>>> but AB voting is support only from a750+. So we can add bcm nodes to
>>>> enable IB voting, but how do we ensure AB voting via GMU is done only on
>>>> a750+.
>>>
>>> Yep, relying on incomplete data in the catalog is not a great way
>>> to ensure that
>>
>> I understood correctly, so I'll add a bool to enable AB voting, but please
>> don't ask me to remove it because it's dead code and useless if only
>> enabled on a750+...
> 
> Can't we just add ">= A7XX_GEN3" check here to decide on GMU AB VOTE?
> For older generation, AB vote should be via icc driver. And that I guess
> is out of the scope of this series.

Sure, I'll do that.

Thanks,
Neil

> 
> -Akhil.
> 
>>
>> Neil
>>
>>>
>>> Konrad
>>
>