Re: [PATCH v3 4/8] drm/msm: Fix cx collapse issue during recovery

[Akhil P Oommen]

On 7/31/2022 9:52 PM, Rob Clark wrote:
> On Sat, Jul 30, 2022 at 2:41 AM Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx> wrote:
> > There are some hardware logic under CX domain. For a successful
> > recovery, we should ensure cx headswitch collapses to ensure all the
> > stale states are cleard out. This is especially true to for a6xx family
> > where we can GMU co-processor.
> >
> > Currently, cx doesn't collapse due to a devlink between gpu and its
> > smmu. So the *struct gpu device* needs to be runtime suspended to ensure
> > that the iommu driver removes its vote on cx gdsc.
> >
> > Signed-off-by: Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx>
> > ---
> >
> > Changes in v3:
> > - Simplied the pm refcount drop since we have just a single refcount now
> > for all active submits
> >
> >   drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 24 +++++++++++++++++++++---
> >   drivers/gpu/drm/msm/msm_gpu.c         |  4 +---
> >   2 files changed, 22 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > index 42ed9a3..1b049c5 100644
> > --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> > @@ -1193,7 +1193,7 @@ static void a6xx_recover(struct msm_gpu *gpu)
> >   {
> >          struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> >          struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> > -       int i;
> > +       int i, active_submits;
> >
> >          adreno_dump_info(gpu);
> >
> > @@ -1210,8 +1210,26 @@ static void a6xx_recover(struct msm_gpu *gpu)
> >           */
> >          gmu_write(&a6xx_gpu->gmu, REG_A6XX_GMU_GMU_PWR_COL_KEEPALIVE, 0);
> >
> > -       gpu->funcs->pm_suspend(gpu);
> > -       gpu->funcs->pm_resume(gpu);
> > +       pm_runtime_dont_use_autosuspend(&gpu->pdev->dev);
> > +
> > +       /* active_submit won't change until we make a submission */
> > +       mutex_lock(&gpu->active_lock);
> > +       active_submits = gpu->active_submits;
> > +       mutex_unlock(&gpu->active_lock);
> > +
> > +       /* Drop the rpm refcount from active submits */
> > +       if (active_submits)
> > +               pm_runtime_put(&gpu->pdev->dev);
> Couldn't this race with an incoming submit triggering active_submits
> to transition 0 -> 1?  Moving the mutex_unlock() would solve this.
>
> Actually, maybe just move the mutex_unlock() to the end of the entire
> sequence.  You could also clear gpu->active_submits and restore it
> before unlocking, so you can drop the removal of the WARN_ON_ONCE
> (patch 6/8) which should otherwise be squashed into this patch to keep
> things bisectable
Because we are holding gpu->lock, there won't be any new submissions to 
gpu. But I agree with your both suggestions.

-Akhil.
> > +
> > +       /* And the final one from recover worker */
> > +       pm_runtime_put_sync(&gpu->pdev->dev);
> > +
> > +       pm_runtime_use_autosuspend(&gpu->pdev->dev);
> > +
> > +       if (active_submits)
> > +               pm_runtime_get(&gpu->pdev->dev);
> > +
> > +       pm_runtime_get_sync(&gpu->pdev->dev);
> >
> >          msm_gpu_hw_init(gpu);
> >   }
> > diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> > index 1945efb..07e55a6 100644
> > --- a/drivers/gpu/drm/msm/msm_gpu.c
> > +++ b/drivers/gpu/drm/msm/msm_gpu.c
> > @@ -426,9 +426,7 @@ static void recover_worker(struct kthread_work *work)
> >                  /* retire completed submits, plus the one that hung: */
> >                  retire_submits(gpu);
> >
> > -               pm_runtime_get_sync(&gpu->pdev->dev);
> >                  gpu->funcs->recover(gpu);
> > -               pm_runtime_put_sync(&gpu->pdev->dev);
> Hmm, could this have some fallout on earlier gens?
>
> I guess I should extend the igt msm_recovery test to run on things
> prior to a6xx..
>
> BR,
> -R
No, because of patch 3/8 in this series.

-Akhil.
> >                  /*
> >                   * Replay all remaining submits starting with highest priority
> > @@ -445,7 +443,7 @@ static void recover_worker(struct kthread_work *work)
> >                  }
> >          }
> >
> > -       pm_runtime_put_sync(&gpu->pdev->dev);
> > +       pm_runtime_put(&gpu->pdev->dev);
> >
> >          mutex_unlock(&gpu->lock);
> >
> > --
> > 2.7.4