On Mon, Mar 7, 2022 at 9:53 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
Introduce fourcc codes for color-indexed frame buffer formats with two,
four, and sixteen colors, and provide a mapping from bit per pixel and
depth to fourcc codes.
As the number of bits per pixel is less than eight, these rely on proper
block handling for the calculation of bits per pixel and pitch.
Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/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 */
After replying to Ilia's comment[1], I realized the CFB drawing
operations use native byte and bit ordering, unless
FBINFO_FOREIGN_ENDIAN is set.
While Amiga, Atari, and Sun-3 use big-endian bit ordering,
e.g. Acorn VIDC[2] uses little endian, and SH7760[3] is configurable
(sh7760fb configures ordering to match host order).
BTW, ssd130{7fb,x}_update_rect() both assume little-endian, so I
guess they are broken on big-endian.
Fbtest uses big-endian bit ordering, so < 8 bpp is probably broken
on little-endian.
Hence the above should become:
#define DRM_FORMAT_C1 fourcc_code('C', '1', ' ', ' ') /*
[7:0] C7:C6:C5:C4:C3:C2:C1:C0 1:1:1:1:1:1:1:1 eight pixels/byte */
#define DRM_FORMAT_C2 fourcc_code('C', '2', ' ', ' ') /*
[7:0] C3:C2:C1:C0 2:2:2:2 four pixels/byte */
#define DRM_FORMAT_C4 fourcc_code('C', '4', ' ', ' ') /*
[7:0] C1:C0 4:4 two pixels/byte */
The same changes should be made for DRM_FORMAT_[RD][124].
The fbdev emulation code should gain support for these with and without
DRM_FORMAT_BIG_ENDIAN, the latter perhaps only on big-endian platforms?
[1] https://lore.kernel.org/r/CAKb7UvgEdm9U=+RyRwL0TGRfA_Qc7NbhCWoZOft2DKdXggtKYw@xxxxxxxxxxxxxx/
[2] See p.30 of the VIDC datasheet
http://chrisacorns.computinghistory.org.uk/docs/Acorn/Misc/Acorn_VIDC_Datasheet.pdf
[3] See p.1178 of the SH7660 datasheet
https://datasheet.octopart.com/HD6417760BL200AV-Renesas-datasheet-14105759.pdf
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
