drm/nouveau: idle channel before releasing notify object

Unmapping it while it's still in use (e.g. by M2MF) can lead to page faults
and a lot of TRAP_M2MF spam in dmesg.
Signed-off-by: NMarcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_abi16.c

@@ -116,6 +116,11 @@ nouveau_abi16_chan_fini(struct nouveau_abi16 *abi16,
 {
 	struct nouveau_abi16_ntfy *ntfy, *temp;
 
+	/* wait for all activity to stop before releasing notify object, which
+	 * may be still in use */
+	if (chan->chan && chan->ntfy)
+		nouveau_channel_idle(chan->chan);
+
 	/* cleanup notifier state */
 	list_for_each_entry_safe(ntfy, temp, &chan->notifiers, head) {
 		nouveau_abi16_ntfy_fini(chan, ntfy);