We should enable semaphores on IVB by default, and on SNB in cases where
dma remapping is disabled or iommu is not enabled.

v2: adapt patch according to the feedback, and put it in line with Keith's
rc6 enabling patch.

CC: Daniel Vetter <[email protected]>
CC: Ben Widawsky <[email protected]>
CC: Keith Packard <[email protected]>
CC: Jesse Barnes <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42696
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=40564
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=41353
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38862
Signed-off-by: Eugeni Dodonov <[email protected]>
---
 drivers/gpu/drm/i915/i915_drv.c            |    4 ++--
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |   24 +++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index cc531bb..83b2be4 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -58,10 +58,10 @@ module_param_named(powersave, i915_powersave, int, 0600);
 MODULE_PARM_DESC(powersave,
                "Enable powersavings, fbc, downclocking, etc. (default: true)");
 
-unsigned int i915_semaphores __read_mostly = 0;
+unsigned int i915_semaphores __read_mostly = -1;
 module_param_named(semaphores, i915_semaphores, int, 0600);
 MODULE_PARM_DESC(semaphores,
-               "Use semaphores for inter-ring sync (default: false)");
+               "Use semaphores for inter-ring sync (default: -1 (use per-chip 
defaults))");
 
 unsigned int i915_enable_rc6 __read_mostly = 0;
 module_param_named(i915_enable_rc6, i915_enable_rc6, int, 0600);
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c 
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 3693e83..c19a063 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -33,6 +33,11 @@
 #include "i915_trace.h"
 #include "intel_drv.h"
 
+#ifdef CONFIG_INTEL_IOMMU
+#include <linux/dma_remapping.h>
+#include <linux/dmar.h>
+#endif
+
 struct change_domains {
        uint32_t invalidate_domains;
        uint32_t flush_domains;
@@ -746,6 +751,23 @@ i915_gem_execbuffer_flush(struct drm_device *dev,
        return 0;
 }
 
+static bool
+intel_enable_semaphores(struct drm_device *dev)
+{
+       if (i915_semaphores >= 0)
+               return i915_semaphores;
+       if (INTEL_INFO(dev)->gen >= 7)
+               return 1;
+#ifdef CONFIG_INTEL_IOMMU
+       /* On gen6, we only enable semaphores if dma remapping is disabled,
+        * or if there is no iommu.
+        */
+       if (INTEL_INFO(dev)->gen == 6)
+               return no_iommu || dmar_disabled;
+#endif
+       return 1;
+}
+
 static int
 i915_gem_execbuffer_sync_rings(struct drm_i915_gem_object *obj,
                               struct intel_ring_buffer *to)
@@ -758,7 +780,7 @@ i915_gem_execbuffer_sync_rings(struct drm_i915_gem_object 
*obj,
                return 0;
 
        /* XXX gpu semaphores are implicated in various hard hangs on SNB */
-       if (INTEL_INFO(obj->base.dev)->gen < 6 || !i915_semaphores)
+       if (INTEL_INFO(obj->base.dev)->gen < 6 || 
!intel_enable_semaphores(obj->base.dev))
                return i915_gem_object_wait_rendering(obj);
 
        idx = intel_ring_sync_index(from, to);
-- 
1.7.7.4

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