ALSA: firewire-lib: add a restriction for a transaction at once

Currently, when waiting for a response, callers can start another
transaction by scheduling another work. This is not good for error
processing of transaction, especially the first response is too late.

This commit serialize request/response transactions, by adding one
boolean member to represent idling state.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/lib.c

@@ -76,6 +76,8 @@ static void async_midi_port_callback(struct fw_card *card, int rcode,
 
 	if (rcode == RCODE_COMPLETE && substream != NULL)
 		snd_rawmidi_transmit_ack(substream, port->consume_bytes);
+
+	port->idling = true;
 }
 
 static void midi_port_work(struct work_struct *work)
@@ -86,6 +88,10 @@ static void midi_port_work(struct work_struct *work)
 	int generation;
 	int type;
 
+	/* Under transacting. */
+	if (!port->idling)
+		return;
+
 	/* Nothing to do. */
 	if (substream == NULL || snd_rawmidi_transmit_empty(substream))
 		return;
@@ -110,6 +116,8 @@ static void midi_port_work(struct work_struct *work)
 		type = TCODE_WRITE_BLOCK_REQUEST;
 
 	/* Start this transaction. */
+	port->idling = false;
+
 	/*
 	 * In Linux FireWire core, when generation is updated with memory
 	 * barrier, node id has already been updated. In this module, After
@@ -150,6 +158,7 @@ int snd_fw_async_midi_port_init(struct snd_fw_async_midi_port *port,
 	port->parent = fw_parent_device(unit);
 	port->addr = addr;
 	port->fill = fill;
+	port->idling = true;
 
 	INIT_WORK(&port->work, midi_port_work);
 

sound/firewire/lib.h

@@ -30,6 +30,7 @@ typedef int (*snd_fw_async_midi_port_fill)(
 struct snd_fw_async_midi_port {
 	struct fw_device *parent;
 	struct work_struct work;
+	bool idling;
 
 	u64 addr;
 	struct fw_transaction transaction;