1 files changed, 19 insertions, 0 deletions

diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 21b944c456f6..0dfd94def593 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -44,6 +44,25 @@ struct drm_fb_helper_crtc {
         int x, y;
 };
 
+/**
+ * struct drm_fb_helper_surface_size - describes fbdev size and scanout surface size
+ * @fb_width: fbdev width
+ * @fb_height: fbdev height
+ * @surface_width: scanout buffer width
+ * @surface_height: scanout buffer height
+ * @surface_bpp: scanout buffer bpp
+ * @surface_depth: scanout buffer depth
+ *
+ * Note that the scanout surface width/height may be larger than the fbdev
+ * width/height.  In case of multiple displays, the scanout surface is sized
+ * according to the largest width/height (so it is large enough for all CRTCs
+ * to scanout).  But the fbdev width/height is sized to the minimum width/
+ * height of all the displays.  This ensures that fbcon fits on the smallest
+ * of the attached displays.
+ *
+ * So what is passed to drm_fb_helper_fill_var() should be fb_width/fb_height,
+ * rather than the surface size.
+ */
 struct drm_fb_helper_surface_size {
         u32 fb_width;
         u32 fb_height;