[Bug 96175] [SKL GT4e] 3D game nexuiz 1.6.1 causes GPU HANG

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96175

--- Comment #24 from mwa <matthew.auld at intel.com> ---
For reference the fix is:

commit ddcfc35f62ed3ad83b100beacb5b30394dcd9960
Author: Ben Widawsky <ben at bwidawsk.net>
Date:   Thu May 26 11:04:07 2016 -0700

    i965/sklgt4: Implement depth/timestamp write w/a

    The stated bug describes a scenario in which a post sync write operation
for
    depth or timestamp can be ignored. There are two workarounds suggested, the
    first and easier is to simply do a cs stall when we do these type of
writes.
    The second option is to do a PIPE_CONTROL flush after the post sync but
before
    the data is required.

    Generally, I believe the data written out is consumed by the application on
the
    CPU side and so doing the easier of the two is ideal. Furthermore, these
queries
    aren't tremendously common in the perf sensitive apps I have looked at.
However,
    there could be cases where a shader stage might directly consume the data,
and
    as a result option 2 may be desirable.

    This patch goes with the easier solution for now.

    gen9lp bug_de_id=2137196

    By itself, this does *not* fix any of the GT4 hangs we're currently
    experiencing.

    Cc: Mika Kuoppala <mika.kuoppala at intel.com>
    Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
    Reviewed-by: Anuj Phogat <anuj.phogat at gmail.com>

There are plans to backport the fix to the next Mesa stable release(should be
11.2.3).

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