drm/ttm: add a way to bo_wait for either the last read or last write

Sometimes we want to know whether a buffer is busy and wait for it (bo_wait).
However, sometimes it would be more useful to be able to query whether
a buffer is busy and being either read or written, and wait until it's stopped
being either read or written. The point of this is to be able to avoid
unnecessary waiting, e.g. if a GPU has written something to a buffer and is now
reading that buffer, and a CPU wants to map that buffer for read, it needs to
only wait for the last write. If there were no write, there wouldn't be any
waiting needed.

This, or course, requires user space drivers to send read/write flags
with each relocation (like we have read/write domains in radeon, so we can
actually use those for something useful now).

Now how this patch works:

The read/write flags should passed to ttm_validate_buffer. TTM maintains
separate sync objects of the last read and write for each buffer, in addition
to the sync object of the last use of a buffer. ttm_bo_wait then operates
with one the sync objects.

Signed-off-by: Marek Olšák <maraeo@gmail.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

2 files changed, 20 insertions, 2 deletions

diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 42e3469..da957bf 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -44,6 +44,11 @@ struct ttm_bo_device;
 
 struct drm_mm_node;
 
+enum ttm_buffer_usage {
+    TTM_USAGE_READ = 1,
+    TTM_USAGE_WRITE = 2,
+    TTM_USAGE_READWRITE = TTM_USAGE_READ | TTM_USAGE_WRITE
+};
 
 /**
  * struct ttm_placement
@@ -174,7 +179,10 @@ struct ttm_tt;
  * the bo_device::lru_lock.
  * @reserved: Deadlock-free lock used for synchronization state transitions.
  * @sync_obj_arg: Opaque argument to synchronization object function.
- * @sync_obj: Pointer to a synchronization object.
+ * @sync_obj: Pointer to a synchronization object of a last read or write,
+ * whichever is later.
+ * @sync_obj_read: Pointer to a synchronization object of a last read.
+ * @sync_obj_write: Pointer to a synchronization object of a last write.
  * @priv_flags: Flags describing buffer object internal state.
  * @vm_rb: Rb node for the vm rb tree.
  * @vm_node: Address space manager node.
@@ -258,6 +266,8 @@ struct ttm_buffer_object {
 
 	void *sync_obj_arg;
 	void *sync_obj;
+	void *sync_obj_read;
+	void *sync_obj_write;
 	unsigned long priv_flags;
 
 	/**
@@ -325,6 +335,7 @@ ttm_bo_reference(struct ttm_buffer_object *bo)
  * @bo:  The buffer object.
  * @interruptible:  Use interruptible wait.
  * @no_wait:  Return immediately if buffer is busy.
+ * @usage:  Whether to wait for the last read and/or the last write.
  *
  * This function must be called with the bo::mutex held, and makes
  * sure any previous rendering to the buffer is completed.
@@ -334,7 +345,8 @@ ttm_bo_reference(struct ttm_buffer_object *bo)
  * Returns -ERESTARTSYS if interrupted by a signal.
  */
 extern int ttm_bo_wait(struct ttm_buffer_object *bo, bool lazy,
-		       bool interruptible, bool no_wait);
+		       bool interruptible, bool no_wait,
+		       enum ttm_buffer_usage usage);
 /**
  * ttm_bo_validate
  *
diff --git a/include/drm/ttm/ttm_execbuf_util.h b/include/drm/ttm/ttm_execbuf_util.h
index 26cc7f9..375f299 100644
--- a/include/drm/ttm/ttm_execbuf_util.h
+++ b/include/drm/ttm/ttm_execbuf_util.h
@@ -41,20 +41,26 @@
  * @bo:             refcounted buffer object pointer.
  * @new_sync_obj_arg: New sync_obj_arg for @bo, to be used once
  * adding a new sync object.
+ * @usage           Indicates how @bo is used by the device.
  * @reserved:       Indicates whether @bo has been reserved for validation.
  * @removed:        Indicates whether @bo has been removed from lru lists.
  * @put_count:      Number of outstanding references on bo::list_kref.
  * @old_sync_obj:   Pointer to a sync object about to be unreferenced
+ * @old_sync_obj_read: Pointer to a read sync object about to be unreferenced.
+ * @old_sync_obj_write: Pointer to a write sync object about to be unreferenced.
  */
 
 struct ttm_validate_buffer {
 	struct list_head head;
 	struct ttm_buffer_object *bo;
 	void *new_sync_obj_arg;
+	enum ttm_buffer_usage usage;
 	bool reserved;
 	bool removed;
 	int put_count;
 	void *old_sync_obj;
+	void *old_sync_obj_read;
+	void *old_sync_obj_write;
 };
 
 /**