[Mesa-dev] [PATCH 0/2] i965: Back-port GPU hang workarounds (bug 50271)

[Paul Berry]

Just looking for a quick patch review to make sure I've backported
these patches to 8.0 correctly (and also confirmation that this
backport is a good idea).  These patches are intended to apply to the
8.0 branch.

The issue is that on Gen6 and Gen7, images rendered to depth and
stencil buffers must be aligned to a multiple of 8 pixels, otherwise
certain rendering operations produce a GPU hang.  Unfortunately, due
to the layout of miptrees (and the fact that we render to depth and
stencil miptrees using coordinate offsets), it would take a lot of
code rework to both produce correct rendering and guarantee no GPU
hangs.

These patches avoid the GPU hangs by forcing the image offsets to be
multiples of 8.  As a result, correct rendering to depth and stencil
miptrees is sacrificed but the GPU doesn't hang.  The sacrifice is
minor, since it only affects miptree levels that would otherwise be
unaligned (in practice this is usually just the smallest miplevels),
and it only matters for (a) rendering to a depth/stencil buffer that
is later used as a texture, or (b) ping-ponging between miplevels
while rendering, both of which are fairly rare.  On the master branch,
we decided that this was a worthwhile compromise.

As a result of this sacrifice, this will regress the following piglit
tests: fbo/fbo-depth-array (Gen6 only),
spec/ARB_depth_buffer_float/fbo-clear-formats,
spec/ARB_depth_texture/fbo-clear-formats, and
spec/EXT_packed_depth_stencil/fbo-clear-formats.  These tests
currently fail on master for the same reason.

For more information see:
https://bugs.freedesktop.org/show_bug.cgi?id=50271

[PATCH 1/2] i965/Gen6: Work around GPU hangs due to misaligned depth coordinate offsets.
[PATCH 2/2] i965/Gen7: Work around GPU hangs due to misaligned depth coordinate offsets.