drm/i915: Insert a command barrier on BLT/BSD cache flushes
This looked like an odd regression from
commit ec5cc0f9b019af95e4571a9fa162d94294c8d90b
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu Jun 12 10:28:55 2014 +0100
drm/i915: Restrict GPU boost to the RCS engine
but in reality it undercovered a much older coherency bug. The issue that
boosting the GPU frequency on the BCS ring was masking was that we could
wake the CPU up after completion of a BCS batch and inspect memory prior
to the write cache being fully evicted. In order to serialise the
breadcrumb interrupt (and so ensure that the CPU's view of memory is
coherent) we need to perform a post-sync operation in the MI_FLUSH_DW.
v2: Fix all the MI_FLUSH_DW (bsd plus the duplication in execlists).
Also fix the invalidate_domains mask in gen8_emit_flush() for ring !=
VCS.
Testcase: gpuX-rcs-gpu-read-after-write
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index a94346f..0f358c5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1211,15 +1211,17 @@
cmd = MI_FLUSH_DW + 1;
- if (ring == &dev_priv->ring[VCS]) {
- if (invalidate_domains & I915_GEM_GPU_DOMAINS)
- cmd |= MI_INVALIDATE_TLB | MI_INVALIDATE_BSD |
- MI_FLUSH_DW_STORE_INDEX |
- MI_FLUSH_DW_OP_STOREDW;
- } else {
- if (invalidate_domains & I915_GEM_DOMAIN_RENDER)
- cmd |= MI_INVALIDATE_TLB | MI_FLUSH_DW_STORE_INDEX |
- MI_FLUSH_DW_OP_STOREDW;
+ /* We always require a command barrier so that subsequent
+ * commands, such as breadcrumb interrupts, are strictly ordered
+ * wrt the contents of the write cache being flushed to memory
+ * (and thus being coherent from the CPU).
+ */
+ cmd |= MI_FLUSH_DW_STORE_INDEX | MI_FLUSH_DW_OP_STOREDW;
+
+ if (invalidate_domains & I915_GEM_GPU_DOMAINS) {
+ cmd |= MI_INVALIDATE_TLB;
+ if (ring == &dev_priv->ring[VCS])
+ cmd |= MI_INVALIDATE_BSD;
}
intel_logical_ring_emit(ringbuf, cmd);