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

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Date:   Tue, 15 Feb 2022 17:52:18 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Helge Deller <deller@....de>,
        Javier Martinez Canillas <javierm@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-m68k@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH 0/8] drm: Add support for low-color frame buffer formats

	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@...ux-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