linux-kernel - Re: [PATCH v2 5/5] drm/msm/dpu: rate limit snapshot capture for mmu faults

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Message-ID: <mbtwyyfryvltkeicgmrzrfas3u35ocathehswi4rme5tbs6r37@plcl6gzpl2ld>
Date: Wed, 18 Dec 2024 13:20:08 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jessica Zhang <quic_jesszhan@...cinc.com>
Cc: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, quic_abhinavk@...cinc.com, linux-arm-msm@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] drm/msm/dpu: rate limit snapshot capture for mmu
 faults

On Tue, Dec 17, 2024 at 04:27:57PM -0800, Jessica Zhang wrote:
> From: Abhinav Kumar <quic_abhinavk@...cinc.com>
> 
> There is no recovery mechanism in place yet to recover from mmu
> faults for DPU. We can only prevent the faults by making sure there
> is no misconfiguration.
> 
> Rate-limit the snapshot capture for mmu faults to once per
> msm_atomic_commit_tail() as that should be sufficient to capture
> the snapshot for debugging otherwise there will be a lot of DPU
> snapshots getting captured for the same fault which is redundant
> and also might affect capturing even one snapshot accurately.
> 
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> ---
>  drivers/gpu/drm/msm/msm_atomic.c | 2 ++
>  drivers/gpu/drm/msm/msm_kms.c    | 5 ++++-
>  drivers/gpu/drm/msm/msm_kms.h    | 3 +++
>  3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
> index 9c45d641b5212c11078ab38c13a519663d85e10a..9ad7eeb14d4336abd9d8a8eb1382bdddce80508a 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -228,6 +228,8 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
>  	if (kms->funcs->prepare_commit)
>  		kms->funcs->prepare_commit(kms, state);
>  
> +	kms->fault_snapshot_capture = 0;
> +

- Please move it before the prepare_commit().
- You are accessing the same variable from different threads / cores.
  There should be some kind of a sync barrier.

>  	/*
>  	 * Push atomic updates down to hardware:
>  	 */
> diff --git a/drivers/gpu/drm/msm/msm_kms.c b/drivers/gpu/drm/msm/msm_kms.c
> index 78830e446355f77154fa21a5d107635bc88ba3ed..3327caf396d4fc905dc127f09515559c12666dc8 100644
> --- a/drivers/gpu/drm/msm/msm_kms.c
> +++ b/drivers/gpu/drm/msm/msm_kms.c
> @@ -168,7 +168,10 @@ static int msm_kms_fault_handler(void *arg, unsigned long iova, int flags, void
>  {
>  	struct msm_kms *kms = arg;
>  
> -	msm_disp_snapshot_state(kms->dev);
> +	if (!kms->fault_snapshot_capture) {
> +		msm_disp_snapshot_state(kms->dev);
> +		kms->fault_snapshot_capture++;
> +	}
>  
>  	return -ENOSYS;
>  }
> diff --git a/drivers/gpu/drm/msm/msm_kms.h b/drivers/gpu/drm/msm/msm_kms.h
> index e60162744c669773b6e5aef824a173647626ab4e..3ac089e26e14b824567f3cd2c62f82a1b9ea9878 100644
> --- a/drivers/gpu/drm/msm/msm_kms.h
> +++ b/drivers/gpu/drm/msm/msm_kms.h
> @@ -128,6 +128,9 @@ struct msm_kms {
>  	int irq;
>  	bool irq_requested;
>  
> +	/* rate limit the snapshot capture to once per attach */
> +	int fault_snapshot_capture;
> +
>  	/* mapper-id used to request GEM buffer mapped for scanout: */
>  	struct msm_gem_address_space *aspace;
>  
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry