[PATCH 1/5] drm/i915: "Flush Me Harder" required on gen6+

Luis Henriques luis.henriques at canonical.com
Tue Apr 9 16:06:15 UTC 2013

From: Daniel Vetter <daniel.vetter at ffwll.ch>

BugLink: http://bugs.launchpad.net/bugs/1140716

The prep to remove the flushing list in

commit cc889e0f6ce6a63c62db17d702ecfed86d58083f
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Wed Jun 13 20:45:19 2012 +0200

    drm/i915: disable flushing_list/gpu_write_list

causes quite some decent regressions. We can fix this by setting the
CS_STALL bit to ensure that the following seqno write happens only
after the cache flush has completed. But only do that when the caller
actually wants the flush (and not also when we invalidate caches
before starting the next batch).

I've looked through all our ancient scrolls about gen6+ pipe control
workarounds, and this seems to be indeed a legal combination: We're
allowed to set the CS_STALL bit when we flush the render cache (which
we do).

While yelling at this code, also pass back the return value from
intel_emit_post_sync_nonzero_flush properly.

v2: Instead of emitting more pipe controls, set the CS_STALL bit on
the write flush as suggested by Chris Wilson. It seems to work, too.

Cc: Eric Anholt <eric at anholt.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51436
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51429
Tested-by: Lu Hua <huax.lu at intel.com>
Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
(cherry picked from commit 97f209bcfc0c5db08d9badf8cbafd489f22a6e44)

Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/gpu/drm/i915/intel_ringbuffer.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d623717..ce87bee 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -219,7 +219,9 @@ gen6_render_ring_flush(struct intel_ring_buffer *ring,
 	int ret;
 	/* Force SNB workarounds for PIPE_CONTROL flushes */
-	intel_emit_post_sync_nonzero_flush(ring);
+	ret = intel_emit_post_sync_nonzero_flush(ring);
+	if (ret)
+		return ret;
 	/* Just flush everything.  Experiments have shown that reducing the
 	 * number of bits based on the write domains has little performance
@@ -232,6 +234,12 @@ gen6_render_ring_flush(struct intel_ring_buffer *ring,
+	/*
+	 * Ensure that any following seqno writes only happen when the render
+	 * cache is indeed flushed (but only if the caller actually wants that).
+	 */
+	if (flush_domains)
 	ret = intel_ring_begin(ring, 6);
 	if (ret)

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