[Bug 96526] [APL BSW BDW] [BAT execlists] Sporadic - gem_exec_suspend basic-s4 GPU hang after resume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96526

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #58 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit bafb2f7d4755bf1571bd5e9a03b97f3fc4fe69ae
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Wed Sep 21 14:51:08 2016 +0100

    drm/i915/execlists: Reset RING registers upon resume

    There is a disparity in the context image saved to disk and our own
    bookkeeping - that is we presume the RING_HEAD and RING_TAIL match our
    stored ce->ring->tail value. However, as we emit WA_TAIL_DWORDS into the
    ring but may not tell the GPU about them, the GPU may be lagging behind
    our bookkeeping. Upon hibernation we do not save stolen pages, presuming
    that their contents are volatile. This means that although we start
    writing into the ring at tail, the GPU starts executing from its HEAD
    and there may be some garbage in between and so the GPU promptly hangs
    upon resume.

    Testcase: igt/gem_exec_suspend/basic-S4
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96526
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
    Link:
http://patchwork.freedesktop.org/patch/msgid/20160921135108.29574-3-chris@chris-wilson.co.uk

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