linux-kernel - Re: [PATCH v6 04/12] drm/panfrost: Handle error when allocating AS number

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Message-ID: <f1cad54b-5f25-4a1a-9e61-c96d72ac3637@arm.com>
Date: Fri, 17 Oct 2025 14:25:16 +0100
From: Steven Price <steven.price@....com>
To: Adrián Larumbe <adrian.larumbe@...labora.com>,
 linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
 Boris Brezillon <boris.brezillon@...labora.com>, kernel@...labora.com,
 Rob Herring <robh@...nel.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH v6 04/12] drm/panfrost: Handle error when allocating AS
 number

On 15/10/2025 01:09, Adrián Larumbe wrote:
> If we reach the beginning of the LRU AS list, then return an error.
> 
> Reviewed-by: Steven Price <steven.price@....com>
> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_job.c     | 6 +++++-
>  drivers/gpu/drm/panfrost/panfrost_mmu.c     | 5 +++--
>  drivers/gpu/drm/panfrost/panfrost_mmu.h     | 2 +-
>  drivers/gpu/drm/panfrost/panfrost_perfcnt.c | 8 ++++++--
>  4 files changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index 0722f297d142..d53e9db945ad 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -217,7 +217,11 @@ static int panfrost_job_hw_submit(struct panfrost_job *job, int js)
>  		goto err_hwsubmit;
>  	}
>  
> -	cfg = panfrost_mmu_as_get(pfdev, job->mmu);
> +	ret = panfrost_mmu_as_get(pfdev, job->mmu);
> +	if (ret < 0)
> +		goto err_hwsubmit;
> +
> +	cfg = ret;
>  
>  	panfrost_devfreq_record_busy(&pfdev->pfdevfreq);
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index 1d696eeea2fa..cf272b167feb 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -258,7 +258,7 @@ static int panfrost_mmu_cfg_init(struct panfrost_mmu *mmu,
>  	}
>  }
>  
> -u32 panfrost_mmu_as_get(struct panfrost_device *pfdev, struct panfrost_mmu *mmu)
> +int panfrost_mmu_as_get(struct panfrost_device *pfdev, struct panfrost_mmu *mmu)
>  {
>  	int as;
>  
> @@ -300,7 +300,8 @@ u32 panfrost_mmu_as_get(struct panfrost_device *pfdev, struct panfrost_mmu *mmu)
>  			if (!atomic_read(&lru_mmu->as_count))
>  				break;
>  		}
> -		WARN_ON(&lru_mmu->list == &pfdev->as_lru_list);
> +		if (WARN_ON(&lru_mmu->list == &pfdev->as_lru_list))
> +			return -EBUSY;

I was about to apply this series, but sparse told me that this is
broken. We're holding the as_lock here, so we need to drop that before
returning.

Thanks,

Steve

>  
>  		list_del_init(&lru_mmu->list);
>  		as = lru_mmu->as;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.h b/drivers/gpu/drm/panfrost/panfrost_mmu.h
> index 022a9a74a114..e6e6966a0cca 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.h
> @@ -16,7 +16,7 @@ void panfrost_mmu_fini(struct panfrost_device *pfdev);
>  void panfrost_mmu_reset(struct panfrost_device *pfdev);
>  void panfrost_mmu_suspend_irq(struct panfrost_device *pfdev);
>  
> -u32 panfrost_mmu_as_get(struct panfrost_device *pfdev, struct panfrost_mmu *mmu);
> +int panfrost_mmu_as_get(struct panfrost_device *pfdev, struct panfrost_mmu *mmu);
>  void panfrost_mmu_as_put(struct panfrost_device *pfdev, struct panfrost_mmu *mmu);
>  
>  struct panfrost_mmu *panfrost_mmu_ctx_get(struct panfrost_mmu *mmu);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> index 718eb44b40f8..7020c0192e18 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> @@ -130,9 +130,11 @@ static int panfrost_perfcnt_enable_locked(struct panfrost_device *pfdev,
>  		goto err_vunmap;
>  	}
>  
> -	perfcnt->user = user;
> +	ret = panfrost_mmu_as_get(pfdev, perfcnt->mapping->mmu);
> +	if (ret < 0)
> +		goto err_vunmap;
>  
> -	as = panfrost_mmu_as_get(pfdev, perfcnt->mapping->mmu);
> +	as = ret;
>  	cfg = GPU_PERFCNT_CFG_AS(as) |
>  	      GPU_PERFCNT_CFG_MODE(GPU_PERFCNT_CFG_MODE_MANUAL);
>  
> @@ -164,6 +166,8 @@ static int panfrost_perfcnt_enable_locked(struct panfrost_device *pfdev,
>  	/* The BO ref is retained by the mapping. */
>  	drm_gem_object_put(&bo->base);
>  
> +	perfcnt->user = user;
> +
>  	return 0;
>  
>  err_vunmap: