[PATCH 0/8] drm: Add support for low-color frame buffer formats

Geert Uytterhoeven
2022-02-15T16:53:09Z

Hi all,

A long outstanding issue with the DRM subsystem has been the lack of
support for low-color displays, as used typically on older desktop
systems and small embedded displays.

This patch series adds support for color-indexed frame buffer formats
with 2, 4, and 16 colors. It has been tested on ARAnyM using a
work-in-progress Atari DRM driver, with text console operation and
fbtest.

Overview:
- Patches 1 and 2 give a working system, albeit with a too large pitch
(line length),
- Patches 3 and 4 reduce memory consumption by correcting the pitch
in case bpp < 8,
- Patches 5 and 6 are untested, but may become useful with DRM
userspace,
- Patches 7 and 8 add more fourcc codes for grayscale and monochrome
frame buffer formats, which may be useful for e.g. the ssd130x and
repaper drivers.

Notes:
- I haven't looked yet into making modetest draw a correct image.
- As this was used on emulated hardware only, and I do not have Atari
hardware, I do not have performance figures to compare with fbdev.
I hope to do proper measuring with an Amiga DRM driver, eventually.

Thanks for your comments!

Geert Uytterhoeven (8):
drm/fourcc: Add DRM_FORMAT_C[124]
drm/fb-helper: Add support for DRM_FORMAT_C[124]
drm/fourcc: Add drm_format_info_bpp() helper
drm/client: Use actual bpp when allocating frame buffers
drm/framebuffer: Use actual bpp for DRM_IOCTL_MODE_GETFB
drm/gem-fb-helper: Use actual bpp for size calculations
drm/fourcc: Add DRM_FORMAT_R[124]
drm/fourcc: Add DRM_FORMAT_D1

drivers/gpu/drm/drm_client.c | 4 +-
drivers/gpu/drm/drm_fb_helper.c | 120 ++++++++++++++-----
drivers/gpu/drm/drm_fourcc.c | 45 +++++++
drivers/gpu/drm/drm_framebuffer.c | 2 +-
drivers/gpu/drm/drm_gem_framebuffer_helper.c | 12 +-
include/drm/drm_fourcc.h | 1 +
include/uapi/drm/drm_fourcc.h | 15 +++
7 files changed, 160 insertions(+), 39 deletions(-)

--
2.25.1

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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