Re: [PATCH v2 12/13] drm/panfrost: Add flag to map GEM object Write-Back Cacheable

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

On 10/10/2025 11:11, Boris Brezillon wrote:
> From: Faith Ekstrand <faith.ekstrand@collabora.com>
> 
> Will be used by the UMD to optimize CPU accesses to buffers
> that are frequently read by the CPU, or on which the access
> pattern makes non-cacheable mappings inefficient.
> 
> Mapping buffers CPU-cached implies taking care of the CPU
> cache maintenance in the UMD, unless the GPU is IO coherent.
> 
> v2:
> - Add more to the commit message
> 
> Signed-off-by: Faith Ekstrand <faith.ekstrand@collabora.com>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

Should we not expose the PANFROST_BO_WB_MMAP flag through
DRM_IOCTL_PANFROST_QUERY_BO_INFO? The documentation states that we
return "Flags passed at creation time", but then this new flag isn't
returned.

Thanks,
Steve

> ---
>  drivers/gpu/drm/panfrost/panfrost_drv.c | 10 ++++++++--
>  drivers/gpu/drm/panfrost/panfrost_gem.c |  3 +++
>  include/uapi/drm/panfrost_drm.h         |  1 +
>  3 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 00c0881fa2f0..0f51b1dc1abc 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -125,6 +125,10 @@ static int panfrost_ioctl_get_param(struct drm_device *ddev, void *data, struct
>  	return 0;
>  }
>  
> +#define PANFROST_BO_FLAGS	(PANFROST_BO_NOEXEC | \
> +				 PANFROST_BO_HEAP | \
> +				 PANFROST_BO_WB_MMAP)
> +
>  static int panfrost_ioctl_create_bo(struct drm_device *dev, void *data,
>  		struct drm_file *file)
>  {
> @@ -134,8 +138,7 @@ static int panfrost_ioctl_create_bo(struct drm_device *dev, void *data,
>  	struct panfrost_gem_mapping *mapping;
>  	int ret;
>  
> -	if (!args->size || args->pad ||
> -	    (args->flags & ~(PANFROST_BO_NOEXEC | PANFROST_BO_HEAP)))
> +	if (!args->size || args->pad || (args->flags & ~PANFROST_BO_FLAGS))
>  		return -EINVAL;
>  
>  	/* Heaps should never be executable */
> @@ -661,6 +664,9 @@ 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)
> +			args->create_flags |= PANFROST_BO_WB_MMAP;
>  	}
>  
>  	drm_gem_object_put(gem_obj);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index da0362202d94..0e8028ee9d1f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -320,6 +320,9 @@ panfrost_gem_create(struct drm_device *dev, size_t size, u32 flags)
>  	bo->noexec = !!(flags & PANFROST_BO_NOEXEC);
>  	bo->is_heap = !!(flags & PANFROST_BO_HEAP);
>  
> +	if (flags & PANFROST_BO_WB_MMAP)
> +		bo->base.map_wc = false;
> +
>  	return bo;
>  }
>  
> diff --git a/include/uapi/drm/panfrost_drm.h b/include/uapi/drm/panfrost_drm.h
> index 5832a291adc4..2c1e28f9dd07 100644
> --- a/include/uapi/drm/panfrost_drm.h
> +++ b/include/uapi/drm/panfrost_drm.h
> @@ -104,6 +104,7 @@ struct drm_panfrost_wait_bo {
>  /* Valid flags to pass to drm_panfrost_create_bo */
>  #define PANFROST_BO_NOEXEC	1
>  #define PANFROST_BO_HEAP	2
> +#define PANFROST_BO_WB_MMAP	4
>  
>  /**
>   * struct drm_panfrost_create_bo - ioctl argument for creating Panfrost BOs.