Re: [PATCH 1/2] drm/msm/a6xx: Clear shadow on suspend

[Jordan Crouse <jcrouse@codeaurora.org>]

On Tue, Nov 10, 2020 at 10:43:59AM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> Clear the shadow rptr on suspend.  Otherwise, when we resume, we can
> have a stale value until CP_WHERE_AM_I executes.  If we suspend near
> the ringbuffer wraparound point, this can lead to a chicken/egg
> situation where we are waiting for ringbuffer space to write the
> CP_WHERE_AM_I (or CP_INIT) packet, because we mistakenly believe that
> the ringbuffer is full (due to stale rptr value in the shadow).
> 
> Fixes errors like:
> 
>   [drm:adreno_wait_ring [msm]] *ERROR* timeout waiting for space in ringbuffer 0
> 
> in the resume path.
> 
> Fixes: d3a569fccfa0 ("drm/msm: a6xx: Use WHERE_AM_I for eligible targets")
> Signed-off-by: Rob Clark <robdclark@chromium.org>

Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>

> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 2f236aadfa9c..fcb0aabbc985 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1043,12 +1043,21 @@ static int a6xx_pm_suspend(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, ret;
>  
>  	trace_msm_gpu_suspend(0);
>  
>  	devfreq_suspend_device(gpu->devfreq.devfreq);
>  
> -	return a6xx_gmu_stop(a6xx_gpu);
> +	ret = a6xx_gmu_stop(a6xx_gpu);
> +	if (ret)
> +		return ret;
> +
> +	if (adreno_gpu->base.hw_apriv || a6xx_gpu->has_whereami)
> +		for (i = 0; i < gpu->nr_rings; i++)
> +			a6xx_gpu->shadow[i] = 0;
> +
> +	return 0;
>  }
>  
>  static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
> -- 
> 2.28.0
> 

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