Re: [PATCH v2 1/7] drm/panfrost: Check another bo field for cache option query

[Steven Price <steven.price@arm.com>]

On 04/06/2026 18:35, Adrián Larumbe wrote:
> When querying the properties of a BO, whether it was created in
> Writeback caching mode for userspace mappings, is recorded in a Panfrost
> BO's wb_mmap field.
> 
> Reported-by: Claude <noreply@anthropic.com>
> Closes: https://gitlab.freedesktop.org/panfrost/linux/-/work_items/88
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Fixes: 62eedf1ccba5 ("drm/panfrost: Add flag to map GEM object Write-Back Cacheable")

This is a subtle change in uABI because bo->base.map_wc reflects the
actual properties of the buffer. So on a coherent device this will
change. But it does match the intention/documentation of the ioctl
(returning the creation flags), and I don't think user space could have
been usefully relying on the current behaviour.

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

> ---
>  drivers/gpu/drm/panfrost/panfrost_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 3d0bdba2a474..cb8e5015847f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -659,7 +659,7 @@ static int panfrost_ioctl_query_bo_info(struct drm_device *dev, void *data,
>  		if (bo->is_heap)
>  			args->create_flags |= PANFROST_BO_HEAP;
>  
> -		if (!bo->base.map_wc)
> +		if (bo->wb_mmap)
>  			args->create_flags |= PANFROST_BO_WB_MMAP;
>  	}
>  
>