linux-kernel - Re: [PATCH v6 05/12] drm/panfrost: Check sgt to know whether pages are already mapped

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Message-ID: <55781116-2c73-40d0-849f-4d8ba21d13f9@arm.com>
Date: Wed, 15 Oct 2025 14:09:03 +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 05/12] drm/panfrost: Check sgt to know whether pages
 are already mapped

On 15/10/2025 01:09, Adrián Larumbe wrote:
> In the MMU's page fault ISR for a heap object, determine whether the
> faulting address belongs to a 2MiB block that was already mapped by
> checking its corresponding sgt in the Panfrost BO.
> 
> This is done in preparation for a future commit in which the MMU mapping
> helper might fail, but the page array is left populated, so this cannot
> be used as a check for an early bail-out.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>

Reviewed-by: Steven Price <steven.price@....com>

> ---
>  drivers/gpu/drm/panfrost/panfrost_mmu.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index cf272b167feb..ba32d99ed854 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -600,10 +600,12 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
>  		refcount_set(&bo->base.pages_use_count, 1);
>  	} else {
>  		pages = bo->base.pages;
> -		if (pages[page_offset]) {
> -			/* Pages are already mapped, bail out. */
> -			goto out;
> -		}
> +	}
> +
> +	sgt = &bo->sgts[page_offset / (SZ_2M / PAGE_SIZE)];
> +	if (sgt->sgl) {
> +		/* Pages are already mapped, bail out. */
> +		goto out;
>  	}
>  
>  	mapping = bo->base.base.filp->f_mapping;
> @@ -625,7 +627,6 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
>  		}
>  	}
>  
> -	sgt = &bo->sgts[page_offset / (SZ_2M / PAGE_SIZE)];
>  	ret = sg_alloc_table_from_pages(sgt, pages + page_offset,
>  					NUM_FAULT_PAGES, 0, SZ_2M, GFP_KERNEL);
>  	if (ret)