ALSA: ump: Add no_process_stream flag

This is another preliminary patch for USB MIDI 2.0 gadget driver.
Add a new flag, no_process_stream, to snd_ump for suppressing the UMP
Stream message handling in UMP core.

Link: https://lore.kernel.org/r/20230621110241.4751-3-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/ump.h

@@ -28,6 +28,7 @@ struct snd_ump_endpoint {
 	u32 stream_wait_for;	/* expected stream message status */
 	bool stream_finished;	/* set when message has been processed */
 	bool parsed;		/* UMP / FB parse finished? */
+	bool no_process_stream;	/* suppress UMP stream messages handling */
 	wait_queue_head_t stream_wait;
 	struct snd_rawmidi_file stream_rfile;
 

sound/core/ump.c

@@ -854,6 +854,10 @@ static void ump_handle_stream_msg(struct snd_ump_endpoint *ump,
 	unsigned int status;
 	int ret;
 
+	/* UMP stream message suppressed (for gadget UMP)? */
+	if (ump->no_process_stream)
+		return;
+
 	BUILD_BUG_ON(sizeof(*msg) != 16);
 	ump_dbg(ump, "Stream msg: %08x %08x %08x %08x\n",
 		buf[0], buf[1], buf[2], buf[3]);