drm/i915: Export our request as a dma-buf fence on the reservation object

If the GEM objects being rendered with in this request have been
exported via dma-buf to a third party, hook ourselves into the dma-buf
reservation object so that the third party can serialise with our
rendering via the dma-buf fences.

Testcase: igt/prime_busy
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470324762-2545-26-git-send-email-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index a1da302..7183474 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -26,14 +26,18 @@
  *
  */
 
+#include <linux/dma_remapping.h>
+#include <linux/reservation.h>
+#include <linux/uaccess.h>
+
 #include <drm/drmP.h>
 #include <drm/i915_drm.h>
+
 #include "i915_drv.h"
+#include "i915_gem_dmabuf.h"
 #include "i915_trace.h"
 #include "intel_drv.h"
 #include "intel_frontbuffer.h"
-#include <linux/dma_remapping.h>
-#include <linux/uaccess.h>
 
 #define  __EXEC_OBJECT_HAS_PIN		(1<<31)
 #define  __EXEC_OBJECT_HAS_FENCE	(1<<30)
@@ -1205,6 +1209,28 @@
 	list_move_tail(&vma->vm_link, &vma->vm->active_list);
 }
 
+static void eb_export_fence(struct drm_i915_gem_object *obj,
+			    struct drm_i915_gem_request *req,
+			    unsigned int flags)
+{
+	struct reservation_object *resv;
+
+	resv = i915_gem_object_get_dmabuf_resv(obj);
+	if (!resv)
+		return;
+
+	/* Ignore errors from failing to allocate the new fence, we can't
+	 * handle an error right now. Worst case should be missed
+	 * synchronisation leading to rendering corruption.
+	 */
+	ww_mutex_lock(&resv->lock, NULL);
+	if (flags & EXEC_OBJECT_WRITE)
+		reservation_object_add_excl_fence(resv, &req->fence);
+	else if (reservation_object_reserve_shared(resv) == 0)
+		reservation_object_add_shared_fence(resv, &req->fence);
+	ww_mutex_unlock(&resv->lock);
+}
+
 static void
 i915_gem_execbuffer_move_to_active(struct list_head *vmas,
 				   struct drm_i915_gem_request *req)
@@ -1224,6 +1250,7 @@
 		obj->base.read_domains = obj->base.pending_read_domains;
 
 		i915_vma_move_to_active(vma, req, vma->exec_entry->flags);
+		eb_export_fence(obj, req, vma->exec_entry->flags);
 		trace_i915_gem_object_change_domain(obj, old_read, old_write);
 	}
 }