[Bug 108656] [CI][BAT bsw] igt at gem_* - fail - Failed assertion: !"GPU hung"

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108656

--- Comment #16 from Chris Wilson <chris at chris-wilson.co.uk> ---
Step 1:

commit 490b8c65b9db45896769e1095e78725775f47b3e (HEAD -> drm-intel-next-queued,
drm-intel/for-linux-next, drm-intel/drm-intel-next-queued)
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Thu Dec 6 08:44:31 2018 +0000

    drm/i915/execlists: Apply a full mb before execution for Braswell

    Braswell is really picky about having our writes posted to memory before
    we execute or else the GPU may see stale values. A wmb() is insufficient
    as it only ensures the writes are visible to other cores, we need a full
    mb() to ensure the writes are in memory and visible to the GPU.

    The most frequent failure in flushing before execution is that we see
    stale PTE values and execute the wrong pages.

    References: 987abd5c62f9 ("drm/i915/execlists: Force write serialisation
into context image vs execution")
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
    Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
    Cc: stable at vger.kernel.org
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

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