[Bug 108820] [SKL] GPU hangs in benchmarks using compute shaders with drm-tip v4.20-rc kernels

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108820

Lionel Landwerlin <lionel.g.landwerlin at linux.intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #8 from Lionel Landwerlin <lionel.g.landwerlin at linux.intel.com> ---
I know this is going to be painful, but it would be really good to have a
bisect on what commit broke this...
Skimming through the logs, I couldn't find anything between drm-tip/4.18-rc7
and drm-tip/4.20-rc4 that indicates a hang of this kind on gen9.

A bit later (4th of December) this fix appeared that could impact  :

commit 4a15c75c42460252a63d30f03b4766a52945fb47
Author: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Date:   Mon Dec 3 13:33:41 2018 +0000

    drm/i915: Introduce per-engine workarounds

    We stopped re-applying the GT workarounds after engine reset since commit
    59b449d5c82a ("drm/i915: Split out functions for different kinds of
    workarounds").

    Issue with this is that some of the GT workarounds live in the MMIO space
    which gets lost during engine resets. So far the registers in 0x2xxx and
    0xbxxx address range have been identified to be affected.

    This losing of applied workarounds has obvious negative effects and can
    even lead to hard system hangs (see the linked Bugzilla).

    Rather than just restoring this re-application, because we have also
    observed that it is not safe to just re-write all GT workarounds after
    engine resets (GPU might be live and weird hardware states can happen),
    we introduce a new class of per-engine workarounds and move only the
    affected GT workarounds over.

    Using the framework introduced in the previous patch, we therefore after
    engine reset, re-apply only the workarounds living in the affected MMIO
    address ranges.

    v2:
     * Move Wa_1406609255:icl to engine workarounds as well.
     * Rename API. (Chris Wilson)
     * Drop redundant IS_KABYLAKE. (Chris Wilson)
     * Re-order engine wa/ init so latest platforms are first. (Rodrigo Vivi)

    Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Bugzilla: https://bugzilla.freedesktop.org/show_bug.cgi?id=107945
    Fixes: 59b449d5c82a ("drm/i915: Split out functions for different kinds of
workarounds")

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