drm/nouveau/abi16: introduce locked variant of nouveau_abi16_get()

USIF already takes the client mutex, but will need access to ABI16 data
in order to provide some limited interoperability.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_abi16.c

@@ -32,11 +32,10 @@
 #include "nouveau_chan.h"
 #include "nouveau_abi16.h"
 
-struct nouveau_abi16 *
-nouveau_abi16_get(struct drm_file *file_priv)
+static struct nouveau_abi16 *
+nouveau_abi16(struct drm_file *file_priv)
 {
 	struct nouveau_cli *cli = nouveau_cli(file_priv);
-	mutex_lock(&cli->mutex);
 	if (!cli->abi16) {
 		struct nouveau_abi16 *abi16;
 		cli->abi16 = abi16 = kzalloc(sizeof(*abi16), GFP_KERNEL);
@@ -59,12 +58,21 @@ nouveau_abi16_get(struct drm_file *file_priv)
 			kfree(cli->abi16);
 			cli->abi16 = NULL;
 		}
-
-		mutex_unlock(&cli->mutex);
 	}
 	return cli->abi16;
 }
 
+struct nouveau_abi16 *
+nouveau_abi16_get(struct drm_file *file_priv)
+{
+	struct nouveau_cli *cli = nouveau_cli(file_priv);
+	mutex_lock(&cli->mutex);
+	if (nouveau_abi16(file_priv))
+		return cli->abi16;
+	mutex_unlock(&cli->mutex);
+	return NULL;
+}
+
 int
 nouveau_abi16_put(struct nouveau_abi16 *abi16, int ret)
 {