Re: [Freedreno] [PATCH 3/3] drm/msm/gpu: Remove mutex from wait_event condition

Rob Clark
2022-03-17T21:07:15Z

On Thu, Mar 17, 2022 at 1:45 PM Akhil P Oommen <quic_akhilpo@quicinc.com> wrote:
>
> On 3/11/2022 5:16 AM, Rob Clark wrote:
> > From: Rob Clark <robdclark@chromium.org>
> >
> > The mutex wasn't really protecting anything before. Before the previous
> > patch we could still be racing with the scheduler's kthread, as that is
> > not necessarily frozen yet. Now that we've parked the sched threads,
> > the only race is with jobs retiring, and that is harmless, ie.
> >
> > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > ---
> > drivers/gpu/drm/msm/adreno/adreno_device.c | 11 +----------
> > 1 file changed, 1 insertion(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> > index 0440a98988fc..661dfa7681fb 100644
> > --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> > +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> > @@ -607,15 +607,6 @@ static int adreno_runtime_resume(struct device *dev)
> > return gpu->funcs->pm_resume(gpu);
> > }
> >
> > -static int active_submits(struct msm_gpu *gpu)
> > -{
> > - int active_submits;
> > - mutex_lock(&gpu->active_lock);
> > - active_submits = gpu->active_submits;
> > - mutex_unlock(&gpu->active_lock);
> I assumed that this lock here was to ensure proper barriers while
> reading active_submits. Is that not required?

There is a spinlock in prepare_to_wait_event() ahead of checking the
condition, which AFAIU is a sufficient barrier

BR,
-R

>
> -Akhil.
> > - return active_submits;
> > -}
> > -
> > static int adreno_runtime_suspend(struct device *dev)
> > {
> > struct msm_gpu *gpu = dev_to_gpu(dev);
> > @@ -669,7 +660,7 @@ static int adreno_system_suspend(struct device *dev)
> > suspend_scheduler(gpu);
> >
> > remaining = wait_event_timeout(gpu->retire_event,
> > - active_submits(gpu) == 0,
> > + gpu->active_submits == 0,
> > msecs_to_jiffies(1000));
> > if (remaining == 0) {
> > dev_err(dev, "Timeout waiting for GPU to suspend\n");
>