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According to mali_kbase, all Bifrost and Valhall GPUs are affected by
issue TSIX_2033. This hardware bug breaks the INTERSECT frame shader
mode when forcing clean_tile_writes. What does that mean?
The hardware considers a tile "clean" if it has been cleared but not
drawn to. Setting clean_tile_write forces the hardware to write back
such "clean" tiles to main memory.
Bifrost hardware supports frame shaders, which insert a rectangle into
every tile according to a configured rule. Frame shaders are used in
Panfrost to implement tile reloads (i.e. LOAD_OP_LOAD). Two modes are
relevant to the current discussion: ALWAYS, which always inserts a frame
shader, and INTERSECT, which tries to only insert where there is
geometry. Normally, we use INTERSECT for tile reloads as it is more
efficient than ALWAYS-- it allows us to skip reloads of tiles that are
discarded and never written back to memory.
From a software perspective, Panfrost's current logic is correct: if we
clear, we set clean_tile_writes, else we use an INTERSECT frame shader.
There is no software interaction between the two.
Unfortunately, there is a hardware interaction. The hardware forces
clean_tile_writes in certain circumstances when AFBC is used.
Ordinarily, this is a hardware implementation detail and invisible to
software. Unfortunately, this implicit clean tile write is enough to
trigger the hardware bug when using INTERSECT. As such, we need to
detect this case and use ALWAYS instead of INTERSECT for correct
results.
Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13205>
(cherry picked from commit
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`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library ====================================================== Source ------ This repository lives at https://gitlab.freedesktop.org/mesa/mesa. Other repositories are likely forks, and code found there is not supported. Build & install --------------- You can find more information in our documentation (`docs/install.rst <https://mesa3d.org/install.html>`_), but the recommended way is to use Meson (`docs/meson.rst <https://mesa3d.org/meson.html>`_): .. code-block:: sh $ mkdir build $ cd build $ meson .. $ sudo ninja install Support ------- Many Mesa devs hang on IRC; if you're not sure which channel is appropriate, you should ask your question on `OFTC's #dri-devel <irc://irc.oftc.net/dri-devel>`_, someone will redirect you if necessary. Remember that not everyone is in the same timezone as you, so it might take a while before someone qualified sees your question. To figure out who you're talking to, or which nick to ping for your question, check out `Who's Who on IRC <https://dri.freedesktop.org/wiki/WhosWho/>`_. The next best option is to ask your question in an email to the mailing lists: `mesa-dev\@lists.freedesktop.org <https://lists.freedesktop.org/mailman/listinfo/mesa-dev>`_ Bug reports ----------- If you think something isn't working properly, please file a bug report (`docs/bugs.rst <https://mesa3d.org/bugs.html>`_). Contributing ------------ Contributions are welcome, and step-by-step instructions can be found in our documentation (`docs/submittingpatches.rst <https://mesa3d.org/submittingpatches.html>`_). Note that Mesa uses gitlab for patches submission, review and discussions.