linux-kernel - Re: [PATCH v3 1/8] drm/msm: Remove unnecessary pm_runtime

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Message-ID: <CAF6AEGsOzd8wMbgpt7bGNdCspNoH4shQfTknwwdyVde8k4zcZw@mail.gmail.com>
Date:   Sun, 31 Jul 2022 08:55:38 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc:     freedreno <freedreno@...ts.freedesktop.org>,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/8] drm/msm: Remove unnecessary pm_runtime_get/put

On Sat, Jul 30, 2022 at 2:41 AM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>
> We already enable gpu power from msm_gpu_submit(), so avoid a duplicate
> pm_runtime_get/put from msm_job_run().
>
> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
> ---
>
> (no changes since v1)
>
>  drivers/gpu/drm/msm/msm_ringbuffer.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
> index 56eecb4..cad4c35 100644
> --- a/drivers/gpu/drm/msm/msm_ringbuffer.c
> +++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
> @@ -29,8 +29,6 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>                 msm_gem_unlock(obj);
>         }
>
> -       pm_runtime_get_sync(&gpu->pdev->dev);
> -

This is removing a _get_sync() and simply relying on a _get() (async)
in msm_gpu_submit().. that seems pretty likely to go badly?  I think
it should probably replace the _get() in msm_gpu_submit() with
_get_sync() (but also since this is changing position of
resume/suspend vs active_lock, please make sure you test with lockdep
enabled)

BR,
-R

>         /* TODO move submit path over to using a per-ring lock.. */
>         mutex_lock(&gpu->lock);
>
> @@ -38,8 +36,6 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>
>         mutex_unlock(&gpu->lock);
>
> -       pm_runtime_put(&gpu->pdev->dev);
> -
>         return dma_fence_get(submit->hw_fence);
>  }
>
> --
> 2.7.4
>