Re: [Freedreno] [PATCH v2 3/7] drm/msm: Fix cx collapse issue during recovery

[Rob Clark <robdclark@gmail.com>]

On Mon, Jul 11, 2022 at 10:05 PM Akhil P Oommen
<quic_akhilpo@quicinc.com> wrote:
>
> On 7/12/2022 4:52 AM, Doug Anderson wrote:
> > Hi,
> >
> > On Fri, Jul 8, 2022 at 11:00 PM Akhil P Oommen <quic_akhilpo@quicinc.com> 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@quicinc.com>
> >> ---
> >>
> >> (no changes since v1)
> >>
> >>   drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 16 ++++++++++++++--
> >>   drivers/gpu/drm/msm/msm_gpu.c         |  2 --
> >>   2 files changed, 14 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >> index 4d50110..7ed347c 100644
> >> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> >> @@ -1278,8 +1278,20 @@ 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);
> >> +       /*
> >> +        * Now drop all the pm_runtime usage count to allow cx gdsc to collapse.
> >> +        * First drop the usage count from all active submits
> >> +        */
> >> +       for (i = gpu->active_submits; i > 0; i--)
> >> +               pm_runtime_put(&gpu->pdev->dev);
> >> +
> >> +       /* And the final one from recover worker */
> >> +       pm_runtime_put_sync(&gpu->pdev->dev);
> >> +
> >> +       for (i = gpu->active_submits; i > 0; i--)
> >> +               pm_runtime_get(&gpu->pdev->dev);
> >> +
> >> +       pm_runtime_get_sync(&gpu->pdev->dev);
> > In response to v1, Rob suggested pm_runtime_force_suspend/resume().
> > Those seem like they would work to me, too. Why not use them?
> Quoting my previous response which I seem to have sent only to Freedreno
> list:
>
> "I believe it is supposed to be used only during system sleep state
> transitions. Btw, we don't want pm_runtime_get() calls from elsewhere to
> fail by disabling RPM here."

The comment about not wanting other runpm calls to fail is valid.. but
that is also solveable, ie. by holding a lock around runpm calls.
Which I think we need to do anyways, otherwise looping over
gpu->active_submits is racey..

I think pm_runtime_force_suspend/resume() is the least-bad option.. or
at least I'm not seeing any obvious alternative that is better

BR,
-R