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: <6c8f7f48-1aae-4336-b66b-5b02609caa57@quicinc.com>
Date: Mon, 16 Dec 2024 16:10:22 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: <neil.armstrong@...aro.org>,
        Konrad Dybcio
	<konrad.dybcio@....qualcomm.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 12/16/2024 3:13 PM, neil.armstrong@...aro.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@...aro.org wrote:
>>>> 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
>>>
>>> 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.

-Akhil.

> 
> Neil
> 
>>
>> Konrad
>