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

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Message-ID: <CACSVV01EhWWohUDQ8n=FQeDuaDcgmYnMBJDMJ8D1Gist1NR4QQ@mail.gmail.com>
Date: Tue, 22 Jul 2025 08:38:16 -0700
From: Rob Clark <rob.clark@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Akhil P Oommen <akhilpo@....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 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.

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