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

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Message-ID: <CACSVV00d4rbNDOLVZJTBNRmUsGyY6Tkwzv0cHRomeYyMXWHZVA@mail.gmail.com>
Date: Tue, 22 Jul 2025 13:13:53 -0700
From: Rob Clark <rob.clark@....qualcomm.com>
To: Akhil P Oommen <akhilpo@....qualcomm.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        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 Tue, Jul 22, 2025 at 12:23 PM Akhil P Oommen
<akhilpo@....qualcomm.com> wrote:
>
> 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.

Hmm, yeah.. I suppose _this_ patch should only skip clamp-to-idle.  It
is a different topic, boost-after-idle.

BR,
-R

> -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
>