drm/amdgpu: introduce AMDGPU_GEM_CREATE_EXPLICIT_SYNC v2

Introduce a flag to signal that access to a BO will be synchronized
through an external mechanism.

Currently all buffers shared between contexts are subject to implicit
synchronization. However, this is only required for protocols that
currently don't support an explicit synchronization mechanism (DRI2/3).

This patch introduces the AMDGPU_GEM_CREATE_EXPLICIT_SYNC, so that
users can specify when it is safe to disable implicit sync.

v2: only disable explicit sync in amdgpu_cs_ioctl

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -705,7 +705,8 @@ static int amdgpu_cs_sync_rings(struct amdgpu_cs_parser *p)
 
 	list_for_each_entry(e, &p->validated, tv.head) {
 		struct reservation_object *resv = e->robj->tbo.resv;
-		r = amdgpu_sync_resv(p->adev, &p->job->sync, resv, p->filp);
+		r = amdgpu_sync_resv(p->adev, &p->job->sync, resv, p->filp,
+				     amdgpu_bo_explicit_sync(e->robj));
 
 		if (r)
 			return r;

drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c

@@ -212,7 +212,9 @@ int amdgpu_gem_create_ioctl(struct drm_device *dev, void *data,
 		      AMDGPU_GEM_CREATE_NO_CPU_ACCESS |
 		      AMDGPU_GEM_CREATE_CPU_GTT_USWC |
 		      AMDGPU_GEM_CREATE_VRAM_CLEARED |
-		      AMDGPU_GEM_CREATE_VM_ALWAYS_VALID))
+		      AMDGPU_GEM_CREATE_VM_ALWAYS_VALID |
+		      AMDGPU_GEM_CREATE_EXPLICIT_SYNC))
+
 		return -EINVAL;
 
 	/* reject invalid gem domains */

drivers/gpu/drm/amd/amdgpu/amdgpu_object.h

@@ -193,6 +193,14 @@ static inline bool amdgpu_bo_gpu_accessible(struct amdgpu_bo *bo)
 	}
 }
 
+/**
+ * amdgpu_bo_explicit_sync - return whether the bo is explicitly synced
+ */
+static inline bool amdgpu_bo_explicit_sync(struct amdgpu_bo *bo)
+{
+	return bo->flags & AMDGPU_GEM_CREATE_EXPLICIT_SYNC;
+}
+
 int amdgpu_bo_create(struct amdgpu_device *adev,
 			    unsigned long size, int byte_align,
 			    bool kernel, u32 domain, u64 flags,

drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c

@@ -169,14 +169,14 @@ int amdgpu_sync_fence(struct amdgpu_device *adev, struct amdgpu_sync *sync,
  *
  * @sync: sync object to add fences from reservation object to
  * @resv: reservation object with embedded fence
- * @shared: true if we should only sync to the exclusive fence
+ * @explicit_sync: true if we should only sync to the exclusive fence
  *
  * Sync to the fence
  */
 int amdgpu_sync_resv(struct amdgpu_device *adev,
 		     struct amdgpu_sync *sync,
 		     struct reservation_object *resv,
-		     void *owner)
+		     void *owner, bool explicit_sync)
 {
 	struct reservation_object_list *flist;
 	struct dma_fence *f;
@@ -191,6 +191,9 @@ int amdgpu_sync_resv(struct amdgpu_device *adev,
 	f = reservation_object_get_excl(resv);
 	r = amdgpu_sync_fence(adev, sync, f);
 
+	if (explicit_sync)
+		return r;
+
 	flist = reservation_object_get_list(resv);
 	if (!flist || r)
 		return r;

drivers/gpu/drm/amd/amdgpu/amdgpu_sync.h

@@ -45,7 +45,8 @@ int amdgpu_sync_fence(struct amdgpu_device *adev, struct amdgpu_sync *sync,
 int amdgpu_sync_resv(struct amdgpu_device *adev,
 		     struct amdgpu_sync *sync,
 		     struct reservation_object *resv,
-		     void *owner);
+		     void *owner,
+		     bool explicit_sync);
 struct dma_fence *amdgpu_sync_peek_fence(struct amdgpu_sync *sync,
 				     struct amdgpu_ring *ring);
 struct dma_fence *amdgpu_sync_get_fence(struct amdgpu_sync *sync);

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c

@@ -1489,7 +1489,8 @@ int amdgpu_copy_buffer(struct amdgpu_ring *ring, uint64_t src_offset,
 	job->vm_needs_flush = vm_needs_flush;
 	if (resv) {
 		r = amdgpu_sync_resv(adev, &job->sync, resv,
-				     AMDGPU_FENCE_OWNER_UNDEFINED);
+				     AMDGPU_FENCE_OWNER_UNDEFINED,
+				     false);
 		if (r) {
 			DRM_ERROR("sync failed (%d).\n", r);
 			goto error_free;
@@ -1581,7 +1582,7 @@ int amdgpu_fill_buffer(struct amdgpu_bo *bo,
 
 	if (resv) {
 		r = amdgpu_sync_resv(adev, &job->sync, resv,
-				     AMDGPU_FENCE_OWNER_UNDEFINED);
+				     AMDGPU_FENCE_OWNER_UNDEFINED, false);
 		if (r) {
 			DRM_ERROR("sync failed (%d).\n", r);
 			goto error_free;

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c

@@ -1035,7 +1035,7 @@ static int amdgpu_vm_wait_pd(struct amdgpu_device *adev, struct amdgpu_vm *vm,
 	int r;
 
 	amdgpu_sync_create(&sync);
-	amdgpu_sync_resv(adev, &sync, vm->root.base.bo->tbo.resv, owner);
+	amdgpu_sync_resv(adev, &sync, vm->root.base.bo->tbo.resv, owner, false);
 	r = amdgpu_sync_wait(&sync, true);
 	amdgpu_sync_free(&sync);
 
@@ -1176,11 +1176,11 @@ static int amdgpu_vm_update_level(struct amdgpu_device *adev,
 			amdgpu_ring_pad_ib(ring, params.ib);
 			amdgpu_sync_resv(adev, &job->sync,
 					 parent->base.bo->tbo.resv,
-					 AMDGPU_FENCE_OWNER_VM);
+					 AMDGPU_FENCE_OWNER_VM, false);
 			if (shadow)
 				amdgpu_sync_resv(adev, &job->sync,
 						 shadow->tbo.resv,
-						 AMDGPU_FENCE_OWNER_VM);
+						 AMDGPU_FENCE_OWNER_VM, false);
 
 			WARN_ON(params.ib->length_dw > ndw);
 			r = amdgpu_job_submit(job, ring, &vm->entity,
@@ -1644,7 +1644,7 @@ static int amdgpu_vm_bo_update_mapping(struct amdgpu_device *adev,
 		goto error_free;
 
 	r = amdgpu_sync_resv(adev, &job->sync, vm->root.base.bo->tbo.resv,
-			     owner);
+			     owner, false);
 	if (r)
 		goto error_free;
 

include/uapi/drm/amdgpu_drm.h

@@ -91,6 +91,8 @@ extern "C" {
 #define AMDGPU_GEM_CREATE_VRAM_CONTIGUOUS	(1 << 5)
 /* Flag that BO is always valid in this VM */
 #define AMDGPU_GEM_CREATE_VM_ALWAYS_VALID	(1 << 6)
+/* Flag that BO sharing will be explicitly synchronized */
+#define AMDGPU_GEM_CREATE_EXPLICIT_SYNC		(1 << 7)
 
 struct drm_amdgpu_gem_create_in  {
 	/** the requested memory size */