linux-kernel - Re: [PATCH 1/2] drm/msm/dpu1: don't choke on disabling the writeback connector

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Message-ID: <8376e3a1-0630-f489-8938-a1c77eaccdf8@quicinc.com>
Date: Tue, 9 Jul 2024 11:42:01 -0700
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>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Chandan
 Uddaraju <chandanu@...eaurora.org>,
        Rajesh Yadav <ryadav@...eaurora.org>,
        Sravanthi Kollukuduru <skolluku@...eaurora.org>,
        Archit Taneja
	<architt@...eaurora.org>
CC: <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Jeykumar
 Sankaran <jsanka@...eaurora.org>, <stable@...r.kernel.org>,
        Leonard Lausen
	<leonard@...sen.nl>
Subject: Re: [PATCH 1/2] drm/msm/dpu1: don't choke on disabling the writeback
 connector



On 7/9/2024 6:48 AM, Dmitry Baryshkov wrote:
> In order to prevent any errors on connector being disabled, move the
> state->crtc check upfront. This should fix the issues during suspend
> when the writeback connector gets forcebly disabled.
> 
> Fixes: 71174f362d67 ("drm/msm/dpu: move writeback's atomic_check to dpu_writeback.c")
> Cc: stable@...r.kernel.org
> Reported-by: Leonard Lausen <leonard@...sen.nl>
> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/57
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> index 16f144cbc0c9..5c172bcf3419 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_writeback.c
> @@ -39,6 +39,13 @@ static int dpu_wb_conn_atomic_check(struct drm_connector *connector,
>   
>   	DPU_DEBUG("[atomic_check:%d]\n", connector->base.id);
>   
> +	crtc = conn_state->crtc;

We are checking for !conn_state a few lines below but we are 
dereferencing conn_state here.

This is bound to hit a smatch error and also does not look right.

If conn_state will always be valid, we should drop that check too rather 
than checking it later.

Coming to the issue itself, I tried checking the logs but it was not clear.

During force disable, were we hitting below check and hence the 
connector was not getting disabled?

else if (conn_state->connector->status != connector_status_connected) {
                 DPU_ERROR("connector not connected %d\n", 
conn_state->connector->status);
                 return -EINVAL;
         }


I did not see this error log there, so can you pls explain where we were 
bailing out? The check seems valid to me.

> +	if (!crtc)
> +		return 0;
> +
> +	if (!conn_state->writeback_job || !conn_state->writeback_job->fb)
> +		return 0;
> +
>   	if (!conn_state || !conn_state->connector) {
>   		DPU_ERROR("invalid connector state\n");
>   		return -EINVAL;
> @@ -47,13 +54,6 @@ static int dpu_wb_conn_atomic_check(struct drm_connector *connector,
>   		return -EINVAL;
>   	}
>   
> -	crtc = conn_state->crtc;
> -	if (!crtc)
> -		return 0;
> -
> -	if (!conn_state->writeback_job || !conn_state->writeback_job->fb)
> -		return 0;
> -
>   	crtc_state = drm_atomic_get_crtc_state(state, crtc);
>   	if (IS_ERR(crtc_state))
>   		return PTR_ERR(crtc_state);
>