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

drivers/gpu/drm/i915/i915_gem_dmabuf.c

@@ -23,9 +23,13 @@
  * Authors:
  *	Dave Airlie <airlied@redhat.com>
  */
+
+#include <linux/dma-buf.h>
+#include <linux/reservation.h>
+
 #include <drm/drmP.h>
+
 #include "i915_drv.h"
-#include <linux/dma-buf.h>
 
 static struct drm_i915_gem_object *dma_buf_to_obj(struct dma_buf *buf)
 {
@@ -218,25 +222,73 @@ static const struct dma_buf_ops i915_dmabuf_ops =  {
 	.end_cpu_access = i915_gem_end_cpu_access,
 };
 
+static void export_fences(struct drm_i915_gem_object *obj,
+			  struct dma_buf *dma_buf)
+{
+	struct reservation_object *resv = dma_buf->resv;
+	struct drm_i915_gem_request *req;
+	unsigned long active;
+	int idx;
+
+	active = __I915_BO_ACTIVE(obj);
+	if (!active)
+		return;
+
+	/* Serialise with execbuf to prevent concurrent fence-loops */
+	mutex_lock(&obj->base.dev->struct_mutex);
+
+	/* Mark the object for future fences before racily adding old fences */
+	obj->base.dma_buf = dma_buf;
+
+	ww_mutex_lock(&resv->lock, NULL);
+
+	for_each_active(active, idx) {
+		req = i915_gem_active_get(&obj->last_read[idx],
+					  &obj->base.dev->struct_mutex);
+		if (!req)
+			continue;
+
+		if (reservation_object_reserve_shared(resv) == 0)
+			reservation_object_add_shared_fence(resv, &req->fence);
+
+		i915_gem_request_put(req);
+	}
+
+	req = i915_gem_active_get(&obj->last_write,
+				  &obj->base.dev->struct_mutex);
+	if (req) {
+		reservation_object_add_excl_fence(resv, &req->fence);
+		i915_gem_request_put(req);
+	}
+
+	ww_mutex_unlock(&resv->lock);
+	mutex_unlock(&obj->base.dev->struct_mutex);
+}
+
 struct dma_buf *i915_gem_prime_export(struct drm_device *dev,
 				      struct drm_gem_object *gem_obj, int flags)
 {
 	struct drm_i915_gem_object *obj = to_intel_bo(gem_obj);
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct dma_buf *dma_buf;
 
 	exp_info.ops = &i915_dmabuf_ops;
 	exp_info.size = gem_obj->size;
 	exp_info.flags = flags;
 	exp_info.priv = gem_obj;
 
-
 	if (obj->ops->dmabuf_export) {
 		int ret = obj->ops->dmabuf_export(obj);
 		if (ret)
 			return ERR_PTR(ret);
 	}
 
-	return dma_buf_export(&exp_info);
+	dma_buf = dma_buf_export(&exp_info);
+	if (IS_ERR(dma_buf))
+		return dma_buf;
+
+	export_fences(obj, dma_buf);
+	return dma_buf;
 }
 
 static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)

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 @@ void i915_vma_move_to_active(struct i915_vma *vma,
 	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 @@ i915_gem_execbuffer_move_to_active(struct list_head *vmas,
 		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);
 	}
 }