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Provide helpers that program hardware gamma LUTs. Tha gamma ramp is either provided by the driver or generated by the helper. The DRM driver exports the GAMMA_LUT property with a fixed number of entries per color component, such as 256 on 8-bit-wide components. The entries describe the gamma ramp of each individual component. The new helper drm_crtc_load_gamma_888() loads such gamma ramp to hardware. The hardware uses each displayed pixel's individial components as indices into the hardware gamma table. For color modes with less than 8 bits per color component, the helpers drm_crtc_load_gamma_565_from() and drm_crtc_load_gamma_555_from_888() interpolate the provided gamma ramp to reduce it to the correct number of entries; 5/6/5 for RGB565-like formats and 5/5/5 for XRGB1555-like formats. If no gamma ramp has been provided, drivers can use the new helper drm_crtc_fill_gamma_888() to load a default gamma ramp with 256 entries per color component. For color modes with less bits, the new helpers drm_crtc_fill_gamma_565() and drm_crtc_fill_gamma_555() are available. The default gamma ramp uses a gamma factor of 1. For color modes with palette, drm_crtc_load_palette_8() load an 8-bit palette into the hardware. If no palette has been specified, drm_crtc_fill_palette_8() load a system-specific default palette. This is currently only a grey-scale palette with increasing luminance, but later patches can change this. For PCs, a VGA default palette could be used. v2: - drop comment on gamma factor of 2.2 (Michel, Pekka) - fix typos in commit description (Javier) Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com> Acked-by: Javier Martinez Canillas <javierm@redhat.com> Link: https://lore.kernel.org/r/20250520094203.30545-2-tzimmermann@suse.de
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.