Re: [PATCH 1/2] drm/msm/gpu: Wait for idle before suspending

[Stephen Boyd <swboyd@chromium.org>]

Quoting Rob Clark (2022-01-06 10:14:46)
> From: Rob Clark <robdclark@chromium.org>
>
> System suspend uses pm_runtime_force_suspend(), which cheekily bypasses
> the runpm reference counts.  This doesn't actually work so well when the
> GPU is active.  So add a reasonable delay waiting for the GPU to become
> idle.

Maybe also say:

Failure to wait during system wide suspend leads to GPU hangs seen on
resume.

>
> Alternatively we could just return -EBUSY in this case, but that has the
> disadvantage of causing system suspend to fail.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  drivers/gpu/drm/msm/adreno/adreno_device.c | 9 +++++++++
>  drivers/gpu/drm/msm/msm_gpu.c              | 3 +++
>  drivers/gpu/drm/msm/msm_gpu.h              | 3 +++
>  3 files changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> index 93005839b5da..b677ca3fd75e 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> @@ -611,6 +611,15 @@ static int adreno_resume(struct device *dev)
>  static int adreno_suspend(struct device *dev)
>  {
>         struct msm_gpu *gpu = dev_to_gpu(dev);
> +       int ret = 0;

Please don't assign and then immediately overwrite.

> +
> +       ret = wait_event_timeout(gpu->retire_event,
> +                                !msm_gpu_active(gpu),
> +                                msecs_to_jiffies(1000));
> +       if (ret == 0) {

The usual pattern is

	long timeleft;

	timeleft = wait_event_timeout(...)
	if (!timeleft) {
		/* no time left; timed out */

Can it be the same pattern here? It helps because people sometimes
forget that wait_event_timeout() returns the time that is left and not
an error code when it times out.

> +               dev_err(dev, "Timeout waiting for GPU to suspend\n");
> +               return -EBUSY;
> +       }
>
>         return gpu->funcs->pm_suspend(gpu);
>  }