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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

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

Konrad