linux-kernel - Re: [PATCH 12/17] drm/msm: Skip devfreq IDLE when possible

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Message-ID: <800f8c9d-5586-46a7-aa83-dfb3b97633e0@oss.qualcomm.com>
Date: Wed, 23 Jul 2025 00:53:10 +0530
From: Akhil P Oommen <akhilpo@....qualcomm.com>
To: rob.clark@....qualcomm.com,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Sean Paul <sean@...rly.run>, Konrad Dybcio <konradybcio@...nel.org>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar
 <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/17] drm/msm: Skip devfreq IDLE when possible

On 7/22/2025 9:08 PM, Rob Clark wrote:
> On Tue, Jul 22, 2025 at 6:50 AM Dmitry Baryshkov
> <dmitry.baryshkov@....qualcomm.com> wrote:
>>
>> On Sun, Jul 20, 2025 at 05:46:13PM +0530, Akhil P Oommen wrote:
>>> When IFPC is supported, devfreq idling is redundant and adds
>>> unnecessary pm suspend/wake latency. So skip it when IFPC is
>>> supported.
>>
>> With this in place we have a dummy devfreq instance which does nothing.
>> Wouldn't it be better to skip registering devfreq if IFPC is supported
>> on the platform?
> 
> devfreq is still scaling the freq.  What is being bypassed is
> essentially a CPU based version of IFPC (because on sc7180 we didn't
> have IFPC
> 
> Currently only a618 and 7c3 enable gpu_clamp_to_idle.. if at some
> point those grew IFPC support we could remove the trickery to drop GPU
> to min freq when it is idle altogether.

There are 2 functionalities here:
1. Clamp-to-idle: enabled only on a618/7c3
2. boost-after-idle: Enabled for all GPUs.

With this patch, we are skipping both when IFPC is supported. In the
absence of latency due to clamp-to-idle, do you think a618 (relatively
weaker GPU) would require boost-after-idle to keep with the
UI/composition workload for its typical configuration (1080p@...z)? If
yes, I should probably create a quirk to disable boost-after-idle for
premium tier GPUs, instead of tying it to IFPC feature.

-Akhil.

> 
> BR,
> -R
> 
>>>
>>> Signed-off-by: Akhil P Oommen <akhilpo@....qualcomm.com>
>>> ---
>>>  drivers/gpu/drm/msm/msm_gpu_devfreq.c | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
>>> index 2e1d5c3432728cde15d91f69da22bb915588fe86..53ef2add5047e7d6b6371af949cab36ce8409372 100644
>>> --- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
>>> +++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
>>> @@ -4,6 +4,7 @@
>>>   * Author: Rob Clark <robdclark@...il.com>
>>>   */
>>>
>>> +#include "adreno/adreno_gpu.h"
>>>  #include "msm_gpu.h"
>>>  #include "msm_gpu_trace.h"
>>>
>>> @@ -300,6 +301,8 @@ void msm_devfreq_active(struct msm_gpu *gpu)
>>>       if (!has_devfreq(gpu))
>>>               return;
>>>
>>> +     if (to_adreno_gpu(gpu)->info->quirks & ADRENO_QUIRK_IFPC)
>>> +             return;
>>>       /*
>>>        * Cancel any pending transition to idle frequency:
>>>        */
>>> @@ -370,6 +373,9 @@ void msm_devfreq_idle(struct msm_gpu *gpu)
>>>       if (!has_devfreq(gpu))
>>>               return;
>>>
>>> +     if (to_adreno_gpu(gpu)->info->quirks & ADRENO_QUIRK_IFPC)
>>> +             return;
>>> +
>>>       msm_hrtimer_queue_work(&df->idle_work, ms_to_ktime(1),
>>>                              HRTIMER_MODE_REL);
>>>  }
>>>
>>> --
>>> 2.50.1
>>>
>>
>> --
>> With best wishes
>> Dmitry