drm/i915: Serialize GTT/Aperture accesses on BXT
authorJon Bloomfield <jon.bloomfield@intel.com>
Wed, 24 May 2017 15:54:11 +0000 (08:54 -0700)
committerJani Nikula <jani.nikula@intel.com>
Wed, 7 Jun 2017 09:23:19 +0000 (12:23 +0300)
commitd86b18a06cf361e12ccdf61ae240d432182d8d6b
tree652e03e80339f5b61362ad95cc65ecc36e46d94e
parent3c2993b8c6143d8a5793746a54eba8f86f95240f
drm/i915: Serialize GTT/Aperture accesses on BXT

BXT has a H/W issue with IOMMU which can lead to system hangs when
Aperture accesses are queued within the GAM behind GTT Accesses.

This patch avoids the condition by wrapping all GTT updates in stop_machine
and using a flushing read prior to restarting the machine.

The stop_machine guarantees no new Aperture accesses can begin while
the PTE writes are being emmitted. The flushing read ensures that
any following Aperture accesses cannot begin until the PTE writes
have been cleared out of the GAM's fifo.

Only FOLLOWING Aperture accesses need to be separated from in flight
PTE updates. PTE Writes may follow tightly behind already in flight
Aperture accesses, so no flushing read is required at the start of
a PTE update sequence.

This issue was reproduced by running
igt/gem_readwrite and
igt/gem_render_copy
simultaneously from different processes, each in a tight loop,
with INTEL_IOMMU enabled.

This patch was originally published as:
drm/i915: Serialize GTT Updates on BXT

[Note: This will cause a performance penalty for some use cases, but
avoiding hangs trumps performance hits. This may need to be worked
around in Mesa to recover the lost performance.]

v2: Move bxt/iommu detection into static function
    Remove #ifdef CONFIG_INTEL_IOMMU protection
    Make function names more reflective of purpose
    Move flushing read into static function

v3: Tidy up for checkpatch.pl

Testcase: igt/gem_concurrent_blit
Signed-off-by: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: John Harrison <john.C.Harrison@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/1495641251-30022-1-git-send-email-jon.bloomfield@intel.com
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
(cherry picked from commit 0ef34ad6222abfa513117515fec720c33a58f105)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
drivers/gpu/drm/i915/i915_drv.h
drivers/gpu/drm/i915/i915_gem_gtt.c