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 5:28 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

see the full explanation here

https://git.codelinaro.org/clo/le/platform/vendor/qcom/opensource/graphics-kernel/-/commit/6026c31a54444b712f7ea36ac1aafaaeef07fa4e

Konrad