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[Why] Overlay planes disappear when the plane's alpha blending mode or global opacity is modified. These are considered UPDATE_TYPE_MEDIUM and trigger the update_mpcc path in the DCN hardware sequencer. On DCN10 we have an "optimization" to avoid touching the blending tree on these updates, but this is actually required behavior based on how update_mpcc is structured. For full updates we acquire a MPCC for the plane, remove it if it already exists then reinsert it after with insert_plane. The call to insert_plane can take an optional mpcc to insert the new one above to preserve the current blending order. The update_mpcc hwseq function doesn't do this so the overlay gets sent to the very bottom of the tree. [How] Copy the check over from DCN10 to DCN20. The only time we need to actually touch the tree really is the full update, so this is also an optimization on top of the fix. Fixing the logic for insert_plane is rather simple (cache the bot_mpcc and pass it to insert_plane) but is a change that impacts most display usecases. For now stick with the optimization. Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com> Reviewed-by: Chris Park <Chris.Park@amd.com> Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
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.