linux-kernel - Re: [PATCH] drm/msm/dpu: make "vblank timeout" more useful

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Date: Thu, 25 Jan 2024 09:14:39 -0800
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Rob Clark
	<robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Daniel
 Vetter <daniel@...ll.ch>
CC: <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/dpu: make "vblank timeout" more useful



On 1/5/2024 3:50 PM, 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.
> Include the actual CTL_FLUSH value into the timeout message. This allows
> us to identify the DPU block that gets stuck.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 2 +-
>   1 file changed, 1 insertion(+), 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..fb34067ab6af 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 +489,7 @@ 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));
>   		return -ETIMEDOUT;
>   	}

Nothing wrong with this change.

But I dont know how much information this is giving to really find out 
what is causing the vblank timeout. Sure, we know which flush bit is 
actually stuck but we dont know why its stuck.

We should add a logic here to get the snapshot on the first vblank 
timeout that way we avoid excessive capture as well similar to the other 
fatal locations of calling snapshot.

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