3 files changed, 21 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 47a42eb6cc43..a1103fc6597d 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;
+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))");
 
 int i915_enable_rc6 __read_mostly = -1;
 module_param_named(i915_enable_rc6, i915_enable_rc6, int, 0600);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 6bcafb5bf7fe..554bef7a3b9c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1002,7 +1002,7 @@ extern int i915_max_ioctl;
 extern unsigned int i915_fbpercrtc __always_unused;
 extern int i915_panel_ignore_lid __read_mostly;
 extern unsigned int i915_powersave __read_mostly;
-extern unsigned int i915_semaphores __read_mostly;
+extern int i915_semaphores __read_mostly;
 extern unsigned int i915_lvds_downclock __read_mostly;
 extern int i915_panel_use_ssc __read_mostly;
 extern int i915_vbt_sdvo_panel_type __read_mostly;
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 3693e83a97f3..c681dc149d2a 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -32,6 +32,7 @@
 #include "i915_drv.h"
 #include "i915_trace.h"
 #include "intel_drv.h"
+#include <linux/dma_remapping.h>
 
 struct change_domains {
         uint32_t invalidate_domains;
@@ -746,6 +747,22 @@ i915_gem_execbuffer_flush(struct drm_device *dev,
         return 0;
 }
 
+static bool
+intel_enable_semaphores(struct drm_device *dev)
+{
+        if (INTEL_INFO(dev)->gen < 6)
+                return 0;
+
+        if (i915_semaphores >= 0)
+                return i915_semaphores;
+
+        /* Enable semaphores on SNB when IO remapping is off */
+        if (INTEL_INFO(dev)->gen == 6)
+                return !intel_iommu_enabled;
+
+        return 1;
+}
+
 static int
 i915_gem_execbuffer_sync_rings(struct drm_i915_gem_object *obj,
                                struct intel_ring_buffer *to)
@@ -758,7 +775,7 @@ 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_enable_semaphores(obj->base.dev))
                 return i915_gem_object_wait_rendering(obj);
 
         idx = intel_ring_sync_index(from, to);