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On glk we can no longer reorder the hw LUTS vs. pipe CSC like we could on earlier platforms, and neither do we have a separate output CSC like on icl+. That means if we use the pipe CSC for YCbCr output we are currently applying the gamma LUT after the RGB->YCbCr conversion, which is just wrong. The further we go from a linear curve the more distorted the resulting colors become. To work around this terrible limitation the best we can do is repurpose the hw degamma LUT as a poor man's gamma LUT. Now that we have the internal pre_csc_lut attachment point that is not particularly hard to do. What makes this less than ideal however is the fact that the hw degamma LUT and gamma LUTs have very different capabilities. The gamma LUT can operate in direct color type modes, whereas the degamma LUT can't and just always operates in interpolated mode. Additionally the degamma LUT is just a single 1D LUT, whereas the gamma LUT is made of three separate 1D LUts (one for each channel). So in order to make this semi-sensible we must also verify the user supplied LUT more less matches the hw degamma LUT capabilities. We still end up losing most of the LUT entries though, so the results might be a bit crap. The other option of flat out rejecting the YCbCr+gamma LUT combo seems extremely likely to just cause a black screen for the user. Eg. pretty sure Xorg always applies some kind of gamma LUT, and if the user then plugs in a display that needs YCbCr output we're toast. Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20221114153732.11773-18-ville.syrjala@linux.intel.com Reviewed-by: Uma Shankar <uma.shankar@intel.com> |
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| README | ||
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 Restructured Text 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.