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

[Akhil P Oommen <quic_akhilpo@quicinc.com>]

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+.

-Akhil

> 
> Neil
> 
>>
>> see the full explanation here
>>
>> https://git.codelinaro.org/clo/le/platform/vendor/qcom/opensource/
>> graphics-kernel/-/commit/6026c31a54444b712f7ea36ac1aafaaeef07fa4e
>>
>> Konrad
>