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
