drm/i915: Restore missing command flush before interrupt on BLT ring

We always skipped flushing the BLT ring if the request flush did not
include the RENDER domain. However, this neglects that we try to flush
the COMMAND domain after every batch and before the breadcrumb interrupt
(to make sure the batch is indeed completed prior to the interrupt
firing and so insuring CPU coherency). As a result of the missing flush,
incoherency did indeed creep in, most notable when using lots of command
buffers and so potentially rewritting an active command buffer (i.e.
the GPU was still executing from it even though the following interrupt
had already fired and the request/buffer retired).

As all ring->flush routines now have the same preconditions, de-duplicate
and move those checks up into i915_gem_flush_ring().

Fixes gem_linear_blit.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35284
Signed-off-by: Chris Wilson <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Tested-by: [e-mail]

drivers/gpu/drm/i915/i915_gem.c

···
 {
 	int ret;
 
+	if (((invalidate_domains | flush_domains) & I915_GEM_GPU_DOMAINS) == 0)
+		return 0;
+
 	trace_i915_gem_ring_flush(ring, invalidate_domains, flush_domains);
 
 	ret = ring->flush(ring, invalidate_domains, flush_domains);
 	if (ret)
 		return ret;
 
-	i915_gem_process_flushing_list(ring, flush_domains);
+	if (flush_domains & I915_GEM_GPU_DOMAINS)
+		i915_gem_process_flushing_list(ring, flush_domains);
+
 	return 0;
 }
 

drivers/gpu/drm/i915/intel_ringbuffer.c

···
 	u32 cmd;
 	int ret;
 
-	if ((invalidate_domains | flush_domains) & I915_GEM_GPU_DOMAINS) {
+	/*
+	 * read/write caches:
+	 *
+	 * I915_GEM_DOMAIN_RENDER is always invalidated, but is
+	 * only flushed if MI_NO_WRITE_FLUSH is unset.  On 965, it is
+	 * also flushed at 2d versus 3d pipeline switches.
+	 *
+	 * read-only caches:
+	 *
+	 * I915_GEM_DOMAIN_SAMPLER is flushed on pre-965 if
+	 * MI_READ_FLUSH is set, and is always flushed on 965.
+	 *
+	 * I915_GEM_DOMAIN_COMMAND may not exist?
+	 *
+	 * I915_GEM_DOMAIN_INSTRUCTION, which exists on 965, is
+	 * invalidated when MI_EXE_FLUSH is set.
+	 *
+	 * I915_GEM_DOMAIN_VERTEX, which exists on 965, is
+	 * invalidated with every MI_FLUSH.
+	 *
+	 * TLBs:
+	 *
+	 * On 965, TLBs associated with I915_GEM_DOMAIN_COMMAND
+	 * and I915_GEM_DOMAIN_CPU in are invalidated at PTE write and
+	 * I915_GEM_DOMAIN_RENDER and I915_GEM_DOMAIN_SAMPLER
+	 * are flushed at any MI_FLUSH.
+	 */
+
+	cmd = MI_FLUSH | MI_NO_WRITE_FLUSH;
+	if ((invalidate_domains|flush_domains) &
+	    I915_GEM_DOMAIN_RENDER)
+		cmd &= ~MI_NO_WRITE_FLUSH;
+	if (INTEL_INFO(dev)->gen < 4) {
 		/*
-		 * read/write caches:
-		 *
-		 * I915_GEM_DOMAIN_RENDER is always invalidated, but is
-		 * only flushed if MI_NO_WRITE_FLUSH is unset.  On 965, it is
-		 * also flushed at 2d versus 3d pipeline switches.
-		 *
-		 * read-only caches:
-		 *
-		 * I915_GEM_DOMAIN_SAMPLER is flushed on pre-965 if
-		 * MI_READ_FLUSH is set, and is always flushed on 965.
-		 *
-		 * I915_GEM_DOMAIN_COMMAND may not exist?
-		 *
-		 * I915_GEM_DOMAIN_INSTRUCTION, which exists on 965, is
-		 * invalidated when MI_EXE_FLUSH is set.
-		 *
-		 * I915_GEM_DOMAIN_VERTEX, which exists on 965, is
-		 * invalidated with every MI_FLUSH.
-		 *
-		 * TLBs:
-		 *
-		 * On 965, TLBs associated with I915_GEM_DOMAIN_COMMAND
-		 * and I915_GEM_DOMAIN_CPU in are invalidated at PTE write and
-		 * I915_GEM_DOMAIN_RENDER and I915_GEM_DOMAIN_SAMPLER
-		 * are flushed at any MI_FLUSH.
+		 * On the 965, the sampler cache always gets flushed
+		 * and this bit is reserved.
 		 */
-
-		cmd = MI_FLUSH | MI_NO_WRITE_FLUSH;
-		if ((invalidate_domains|flush_domains) &
-		    I915_GEM_DOMAIN_RENDER)
-			cmd &= ~MI_NO_WRITE_FLUSH;
-		if (INTEL_INFO(dev)->gen < 4) {
-			/*
-			 * On the 965, the sampler cache always gets flushed
-			 * and this bit is reserved.
-			 */
-			if (invalidate_domains & I915_GEM_DOMAIN_SAMPLER)
-				cmd |= MI_READ_FLUSH;
-		}
-		if (invalidate_domains & I915_GEM_DOMAIN_INSTRUCTION)
-			cmd |= MI_EXE_FLUSH;
-
-		if (invalidate_domains & I915_GEM_DOMAIN_COMMAND &&
-		    (IS_G4X(dev) || IS_GEN5(dev)))
-			cmd |= MI_INVALIDATE_ISP;
-
-		ret = intel_ring_begin(ring, 2);
-		if (ret)
-			return ret;
-
-		intel_ring_emit(ring, cmd);
-		intel_ring_emit(ring, MI_NOOP);
-		intel_ring_advance(ring);
+		if (invalidate_domains & I915_GEM_DOMAIN_SAMPLER)
+			cmd |= MI_READ_FLUSH;
 	}
+	if (invalidate_domains & I915_GEM_DOMAIN_INSTRUCTION)
+		cmd |= MI_EXE_FLUSH;
+
+	if (invalidate_domains & I915_GEM_DOMAIN_COMMAND &&
+	    (IS_G4X(dev) || IS_GEN5(dev)))
+		cmd |= MI_INVALIDATE_ISP;
+
+	ret = intel_ring_begin(ring, 2);
+	if (ret)
+		return ret;
+
+	intel_ring_emit(ring, cmd);
+	intel_ring_emit(ring, MI_NOOP);
+	intel_ring_advance(ring);
 
 	return 0;
 }
···
 	       u32     flush_domains)
 {
 	int ret;
-
-	if ((flush_domains & I915_GEM_DOMAIN_RENDER) == 0)
-		return 0;
 
 	ret = intel_ring_begin(ring, 2);
 	if (ret)
···
 	uint32_t cmd;
 	int ret;
 
-	if (((invalidate | flush) & I915_GEM_GPU_DOMAINS) == 0)
-		return 0;
-
 	ret = intel_ring_begin(ring, 4);
 	if (ret)
 		return ret;
···
 {
 	uint32_t cmd;
 	int ret;
-
-	if (((invalidate | flush) & I915_GEM_DOMAIN_RENDER) == 0)
-		return 0;
 
 	ret = blt_ring_begin(ring, 4);
 	if (ret)