Re: [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 <jfale...@redhat.com>

Signed-off-by: Thomas Zimmermann <tzimmerm...@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;