[PATCH 3/3] drm/ast: Validate display modes against framebuffer and format limits

[Jocelyn Falempe]

On 24/03/2025 10:44, Thomas Zimmermann wrote:
> Reimplement ast_mode_config_mode_valid() with DRM format helpers and
> ast's helpers for framebuffer size calculation. Replaces ast's open-
> coded assumptions on bpp and page-alignments.
> 

Thanks, it looks good to me.

Reviewed-by: Jocelyn Falempe <jfalempe at redhat.com>

> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>   drivers/gpu/drm/ast/ast_mode.c | 24 +++++++++++++++---------
>   1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index d3ed27faefd1..a9a3252ff3c2 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -51,6 +51,8 @@
>   
>   #define AST_LUT_SIZE 256
>   
> +#define AST_PRIMARY_PLANE_MAX_OFFSET	(BIT(16) - 1)
> +
>   static unsigned long ast_fb_vram_offset(void)
>   {
>   	return 0; // with shmem, the primary plane is always at offset 0
> @@ -960,16 +962,20 @@ static const struct drm_mode_config_helper_funcs ast_mode_config_helper_funcs =
>   static enum drm_mode_status ast_mode_config_mode_valid(struct drm_device *dev,
>   						       const struct drm_display_mode *mode)
>   {
> -	static const unsigned long max_bpp = 4; /* DRM_FORMAT_XRGB8888 */
> +	const struct drm_format_info *info = drm_format_info(DRM_FORMAT_XRGB8888);
>   	struct ast_device *ast = to_ast_device(dev);
> -	unsigned long fbsize, fbpages, max_fbpages;
> -
> -	max_fbpages = ast_fb_vram_size(ast) >> PAGE_SHIFT;
> -
> -	fbsize = mode->hdisplay * mode->vdisplay * max_bpp;
> -	fbpages = DIV_ROUND_UP(fbsize, PAGE_SIZE);
> -
> -	if (fbpages > max_fbpages)
> +	unsigned long max_fb_size = ast_fb_vram_size(ast);
> +	u64 pitch;
> +
> +	if (drm_WARN_ON_ONCE(dev, !info))
> +		return MODE_ERROR; /* driver bug */
> +
> +	pitch = drm_format_info_min_pitch(info, 0, mode->hdisplay);
> +	if (!pitch)
> +		return MODE_BAD_WIDTH;
> +	if (pitch > AST_PRIMARY_PLANE_MAX_OFFSET)
> +		return MODE_BAD_WIDTH; /* maximum programmable pitch */
> +	if (pitch > max_fb_size / mode->vdisplay)
>   		return MODE_MEM;
>   
>   	return MODE_OK;