• Chris Wilson's avatar
    drm/i915: Disable PSMI sleep messages on all rings around context switches · 2c550183
    Chris Wilson authored
    There exists a current workaround to prevent a hang on context switch
    should the ring go to sleep in the middle of the restore,
    WaProgramMiArbOnOffAroundMiSetContext (applicable to all gen7+). In
    spite of disabling arbitration (which prevents the ring from powering
    down during the critical section) we were still hitting hangs that had
    the hallmarks of the known erratum. That is we are still seeing hangs
    "on the last instruction in the context restore". By comparing -nightly
    (broken) with requests (working), we were able to deduce that it was the
    semaphore LRI cross-talk that reproduced the original failure. The key
    was that requests implemented deferred semaphore signalling, and
    disabling that, i.e. emitting the semaphore signal to every other ring
    after every batch restored the frequent hang.  Explicitly disabling PSMI
    sleep on the RCS ring was insufficient, all the rings had to be awake to
    prevent the hangs. Fortunately, we can reduce the wakelock to the
    MI_SET_CONTEXT operation itself, and so should be able to limit the extra
    power implications.
    
    Since the MI_ARB_ON_OFF workaround is listed for all gen7 and above
    products, we should apply this extra hammer for all of the same
    platforms despite so far that we have only been able to reproduce the
    hang on certain ivb and hsw models. The last question is whether we want
    to always use the extra hammer or only when we know semaphores are in
    operation. At the moment, we only use LRI on non-RCS rings for
    semaphores, but that may change in the future with the possibility of
    reintroducing this bug under subtle conditions.
    
    v2: Make it explicit that the PSMI LRI are an extension to the original
    workaround for the other rings.
    v3: Bikeshedding variable names and whitespacing
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80660
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=83677
    Cc: Simon Farnsworth <simon@farnz.org.uk>
    Cc: Daniel Vetter <daniel@ffwll.ch>
    Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Tested-by: default avatarPeter Frühberger <fritsch@xbmc.org>
    Reviewed-by: default avatarDaniel Vetter <daniel@ffwll.ch>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
    2c550183
i915_gem_context.c 23 KB