[PATCH/RFC libdrm v2 03/10] drm_fourcc: Add DRM_FORMAT_C[124]

[Geert Uytterhoeven <geert@linux-m68k.org>]

Introduce fourcc codes for color-indexed frame buffer formats with two,
four, and sixteen colors.

The fill order (the order in which multiple pixels are packed in a byte)
is the same order as used for indexed-color (2, 4, and 16 colors) images
in the PNG specification, Version 1.2.
This order is also the recommended and default order (FillOrder = 1) for
palette-color (16 colors) images in the TIFF 6.0 Specification, and is
also used for 16-color Linux frame buffer logos.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Marked RFC, as this patch should be replaced by a proper sync with
Linux' include/drm/drm_fourcc.h, once accepted.

https://gitlab.freedesktop.org/mesa/drm/-/blob/main/include/drm/README
section "When and how to update these files".

v2:
  - Split off changes to include/drm/drm_fourcc.h,
  - Improve description.
---
 include/drm/drm_fourcc.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/drm/drm_fourcc.h b/include/drm/drm_fourcc.h
index c668ffb877f1b777..789c7a180cf559af 100644
--- a/include/drm/drm_fourcc.h
+++ b/include/drm/drm_fourcc.h
@@ -99,7 +99,10 @@ extern "C" {
 #define DRM_FORMAT_INVALID	0
 
 /* color index */
-#define DRM_FORMAT_C8		fourcc_code('C', '8', ' ', ' ') /* [7:0] C */
+#define DRM_FORMAT_C1		fourcc_code('C', '1', ' ', ' ') /* [7:0] C0:C1:C2:C3:C4:C5:C6:C7 1:1:1:1:1:1:1:1 eight pixels/byte */
+#define DRM_FORMAT_C2		fourcc_code('C', '2', ' ', ' ') /* [7:0] C0:C1:C2:C3 2:2:2:2 four pixels/byte */
+#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 one pixel/byte */
 
 /* 8 bpp Red */
 #define DRM_FORMAT_R8		fourcc_code('R', '8', ' ', ' ') /* [7:0] R */
-- 
2.25.1