drm/fourcc: Clarify the meaning of single-channel "red"

Traditionally, the first channel has been called the "red" channel, but
the fourcc values for single-channel "red" formats can also be used for
other single-channel formats with a direct relationship between channel
value and brightness, like grayscale.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/31d1792f26707a7270347e9916b4103470d2b192.1657294931.git.geert@linux-m68k.org

diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index b9c746c..9521057 100644 (file)
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -104,16 +104,16 @@ extern "C" {
 #define DRM_FORMAT_C4          fourcc_code('C', '4', ' ', ' ') /* [7:0] C0:C1 4:4 two pixels/byte */
 #define DRM_FORMAT_C8          fourcc_code('C', '8', ' ', ' ') /* [7:0] C */
 
-/* 8 bpp Red */
+/* 8 bpp Red (direct relationship between channel value and brightness) */
 #define DRM_FORMAT_R8          fourcc_code('R', '8', ' ', ' ') /* [7:0] R */
 
-/* 10 bpp Red */
+/* 10 bpp Red (direct relationship between channel value and brightness) */
 #define DRM_FORMAT_R10         fourcc_code('R', '1', '0', ' ') /* [15:0] x:R 6:10 little endian */
 
-/* 12 bpp Red */
+/* 12 bpp Red (direct relationship between channel value and brightness) */
 #define DRM_FORMAT_R12         fourcc_code('R', '1', '2', ' ') /* [15:0] x:R 4:12 little endian */
 
-/* 16 bpp Red */
+/* 16 bpp Red (direct relationship between channel value and brightness) */
 #define DRM_FORMAT_R16         fourcc_code('R', '1', '6', ' ') /* [15:0] R little endian */
 
 /* 16 bpp RG */