[PATCH v2 1/7] drm/fb: document drm_fb_helper_surface_size

[Rob Clark <robdclark@gmail.com>]

There has been some confusion about this struct.  Lack of documentation
probably didn't help.

Signed-off-by: Rob Clark <robdclark@gmail.com>
---
 include/drm/drm_fb_helper.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 21b944c..0dfd94def 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;
-- 
2.1.0

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