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

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Message-ID: <9dcf26e5-1c25-4a18-ab01-58ddf3fbd607@linaro.org>
Date: Fri, 13 Dec 2024 17:40:59 +0100
From: neil.armstrong@...aro.org
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Akhil P Oommen <quic_akhilpo@...cinc.com>, Rob Clark <robdclark@...il.com>,
 Sean Paul <sean@...rly.run>, Konrad Dybcio <konradybcio@...nel.org>,
 Abhinav Kumar <quic_abhinavk@...cinc.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Marijn Suijten <marijn.suijten@...ainline.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH v5 4/7] drm/msm: adreno: find bandwidth index of OPP and
 set it along freq index

On 13/12/2024 17:31, Konrad Dybcio wrote:
> On 13.12.2024 5:28 PM, neil.armstrong@...aro.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@...aro.org>
>>>>>>> Reviewed-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>>>>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.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

Neil

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