[Intel-gfx] [PATCH] drm/i915: enable semaphores on gen6 if dmar is not active

[Daniel Vetter]

Inspired by the recent ppgtt regression report, where switching of
dmar only for the gpu seems to fix things completely, I've looked
again at the semaphores+vt-d situation.

Contrary to my earlier testing a few months back my system is now
stable with dmar disabled for the igd, and not only when disabling
dmar completely.

So I'm rather hopeful that all our recent fixes for snb have changed
things for code and it's time to try enabling semaphores again. We've
also had issues with enabling semaphores which are not vt-d related,
but I guess these are all fixed by the autoreport-disabling and lazy
request fix. And there's only one way to find out whether there are
still other issues ...

When I've tried to apply this patch I've noticed that semaphores on
gen6 have already silently been added in

commit 2911a35b2e4eb87ec48d03aeb11f019e51ae3c0d
Author: Ben Widawsky <ben at bwidawsk.net>
Date:   Thu Apr 5 14:47:36 2012 -0700

    drm/i915: use semaphores for the display plane

Fix this up by only checking whether dmar is enabled on the gfx (not
on the entire system).

Cc: Ben Widawsky <ben at bwidawsk.net>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 77b7a50..1ccfc23 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -407,9 +407,11 @@ bool i915_semaphore_is_enabled(struct drm_device *dev)
 	if (i915_semaphores >= 0)
 		return i915_semaphores;
 
+#ifdef CONFIG_INTEL_IOMMU
 	/* Enable semaphores on SNB when IO remapping is off */
-	if (INTEL_INFO(dev)->gen == 6)
-		return !intel_iommu_enabled;
+	if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped)
+		return false;
+#endif
 
 	return 1;
 }
-- 
1.7.10