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 on 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 supporting 2, 4, 16, and 256 colors, with text console operation, fbtest, and modetest.
Overview: - Patch 1 introduces a helper, to be used by later patches in the series, - Patch 2 introduces a flag to indicate color-indexed formats, - Patches 3 and 4 correct calculations of bits per pixel for sub-byte pixel formats, - Patches 5 and 6 introduce the new C[124] formats, - Patch 7 fixes an untested code path, - Patch 8 documents the use of "red" for light-on-dark displays, - Patches 9 and 10 add more fourcc codes for light-on-dark and dark-on-light frame buffer formats, which may be useful for e.g. the ssd130x and repaper drivers.
Changes compared to v1[1]: - Reshuffle patches, - New patch "[PATCH v2 02/10] drm/fourcc: Add drm_format_info.is_color_indexed flag", - Improve pixel descriptions, - Require depth to match bpp in drm_mode_legacy_fb_format(), - Set .is_color_indexed flag. - Use drm_format_info_bpp() helper instead of deprecated .depth field or format-dependent calculations, - Use new .is_color_indexed field instead of checking against a list of formats, - Add Acked-by, - Replace FIXME by TODO comment, - New patch "[PATCH v2 08/10] [RFC] drm/fourcc: Document that single-channel "red" can be any color", - Add rationale for adding new formats, - Add D[248] for completeness.
Notes: - Using modetest with the C4 formats requires [2]. - Using modetest with the default XR24 format requires [3]. - 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!
[1] "[PATCH 0/8] drm: Add support for low-color frame buffer formats" https://lore.kernel.org/r/20220215165226.2738568-1-geert@linux-m68k.org/ [2] "[PATCH libdrm 0/3] Add support for low-color frame buffer formats" https://lore.kernel.org/r/cover.1646683737.git.geert@linux-m68k.org [3] "[PATCH RFC libdrm 0/2] Big-endian fixes" https://lore.kernel.org/r/cover.1646684158.git.geert@linux-m68k.org
Geert Uytterhoeven (10): drm/fourcc: Add drm_format_info_bpp() helper drm/fourcc: Add drm_format_info.is_color_indexed flag drm/client: Use actual bpp when allocating frame buffers drm/framebuffer: Use actual bpp for DRM_IOCTL_MODE_GETFB drm/fourcc: Add DRM_FORMAT_C[124] drm/fb-helper: Add support for DRM_FORMAT_C[124] [RFC] drm/gem-fb-helper: Use actual bpp for size calculations [RFC] drm/fourcc: Document that single-channel "red" can be any color [RFC] drm/fourcc: Add DRM_FORMAT_R[124] [RFC] drm/fourcc: Add DRM_FORMAT_D[1248]
drivers/gpu/drm/drm_client.c | 4 +- drivers/gpu/drm/drm_fb_helper.c | 101 ++++++++++++++----- drivers/gpu/drm/drm_fourcc.c | 55 +++++++++- drivers/gpu/drm/drm_framebuffer.c | 2 +- drivers/gpu/drm/drm_gem_framebuffer_helper.c | 12 +-- include/drm/drm_fourcc.h | 4 + include/uapi/drm/drm_fourcc.h | 36 +++++-- 7 files changed, 169 insertions(+), 45 deletions(-)