[PATCH] drm_fourcc: Document linear modifier

[Daniel Vetter]

Not setting the fb modifiers flag is something different from setting
the fb modifiers to 0 (which means explicitly linear). We kinda failed
to document that properly. Spotted by Kristian.

Cc: hoegsberg at google.com
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 include/uapi/drm/drm_fourcc.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index da49f69e4d7e..2fca7e1f6aab 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -172,6 +172,16 @@ extern "C" {
  * authoritative source for all of these.
  */
 
+/*
+ * Linear Layout
+ *
+ * Just plain linear layout. Note that this is different from no specifying any
+ * modifier (e.g. not setting DRM_MODE_FB_MODIFIERS in the DRM_ADDFB2 ioctl),
+ * which tells the driver to also take driver-internal information into account
+ * and so might actually result in a tiled framebuffer.
+ */
+#define DRM_FORMAT_MOD_LINEAR	fourcc_mod_code(NONE, 0)
+
 /* Intel framebuffer modifiers */
 
 /*
-- 
2.7.4