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)
committerChris Wilson <chris@chris-wilson.co.uk>
Thu, 25 May 2017 11:45:50 +0000 (12:45 +0100)
commit0ef34ad6222abfa513117515fec720c33a58f105
treec7c07bfa1dd068887d2c4a3fd690af9714185e06
parent22284f400a4dcf48824d96142c0acb75c0c94fba
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

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>
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>
drivers/gpu/drm/i915/i915_drv.h
drivers/gpu/drm/i915/i915_gem_gtt.c