Re: [PATCH v2] drm/msm/dpu: make "vblank timeout" more useful

[Abhinav Kumar <quic_abhinavk@quicinc.com>]

On 2/8/2024 6:50 AM, Dmitry Baryshkov wrote:
> We have several reports of vblank timeout messages. However after some
> debugging it was found that there might be different causes to that.
> To allow us to identify the DPU block that gets stuck, include the
> actual CTL_FLUSH value into the timeout message and trigger the devcore
> snapshot capture.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---
> Changes in v2:
> - Added a call to msm_disp_snapshot_state() to trigger devcore dump
>    (Abhinav)
> - Link to v1: https://lore.kernel.org/r/20240106-fd-dpu-debug-timeout-v1-1-6d9762884641@linaro.org
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> index d0f56c5c4cce..a8d6165b3c0a 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> @@ -489,7 +489,8 @@ static int dpu_encoder_phys_vid_wait_for_commit_done(
>   		(hw_ctl->ops.get_flush_register(hw_ctl) == 0),
>   		msecs_to_jiffies(50));
>   	if (ret <= 0) {
> -		DPU_ERROR("vblank timeout\n");
> +		DPU_ERROR("vblank timeout: %x\n", hw_ctl->ops.get_flush_register(hw_ctl));
> +		msm_disp_snapshot_state(phys_enc->parent->dev);


There is no rate limiting in this piece of code unfortunately. So this 
will flood the number of snapshots.

Short-term solution is you can go with a vblank_timeout_cnt and reset it 
in the enable() like other similar error counters.

long-term solution is we need to centralize these error locations to one 
single dpu_encoder_error_handler() with a single counter and the error 
handler will print out the error code along with the snapshot instead of 
the snapshot being called from all over the place.



>   		return -ETIMEDOUT;
>   	}
>   
> 
> ---
> base-commit: 39676dfe52331dba909c617f213fdb21015c8d10
> change-id: 20240106-fd-dpu-debug-timeout-e917f0bc8063
> 
> Best regards,