ALSA: firewire-lib: add helper functions for asynchronous transactions to transfer MIDI messages

Some models receive MIDI messages via IEEE 1394 asynchronous transactions.
In this case, MIDI messages are transferred in fixed-length payload. It's
nice that firewire-lib module has common helper functions.

This commit implements this idea. Each driver adds
'struct snd_fw_async_midi_port' in its instance structure. In probing,
it should call snd_fw_async_midi_port_init() to initialize the
structure with some parameters such as target address, the length
of payload in a transaction and a pointer for callback function
to fill the payload buffer. At 'struct snd_rawmidi_ops.trigger()'
callback, it should call 'snd_fw_async_midi_port_run()' to start
transactions. Each driver should ensure that the lifetime of MIDI
substream continues till calling 'snd_fw_async_midi_port_finish()'.

The helper functions support retries to transferring MIDI messages when
transmission errors occur. When transactions are successful, the helper
functions call 'snd_rawmidi_transmit_ack()' internally to consume MIDI
bytes in the buffer. Therefore, Each driver is expected to use
'snd_rawmidi_transmit_peek()' to tell the number of bytes to transfer to
return value of 'fill' callback.

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

1 files changed, 103 insertions, 0 deletions

diff --git a/sound/firewire/lib.c b/sound/firewire/lib.c
index 7409edb..03ada3f 100644
--- a/sound/firewire/lib.c
+++ b/sound/firewire/lib.c
@@ -9,6 +9,7 @@
 #include <linux/device.h>
 #include <linux/firewire.h>
 #include <linux/module.h>
+#include <linux/slab.h>
 #include "lib.h"
 
 #define ERROR_RETRY_DELAY_MS	20
@@ -66,6 +67,108 @@ int snd_fw_transaction(struct fw_unit *unit, int tcode,
 }
 EXPORT_SYMBOL(snd_fw_transaction);
 
+static void async_midi_port_callback(struct fw_card *card, int rcode,
+				     void *data, size_t length,
+				     void *callback_data)
+{
+	struct snd_fw_async_midi_port *port = callback_data;
+	struct snd_rawmidi_substream *substream = ACCESS_ONCE(port->substream);
+
+	if (rcode == RCODE_COMPLETE && substream != NULL)
+		snd_rawmidi_transmit_ack(substream, port->consume_bytes);
+}
+
+static void midi_port_work(struct work_struct *work)
+{
+	struct snd_fw_async_midi_port *port =
+			container_of(work, struct snd_fw_async_midi_port, work);
+	struct snd_rawmidi_substream *substream = ACCESS_ONCE(port->substream);
+	int generation;
+	int type;
+
+	/* Nothing to do. */
+	if (substream == NULL || snd_rawmidi_transmit_empty(substream))
+		return;
+
+	/*
+	 * Fill the buffer. The callee must use snd_rawmidi_transmit_peek().
+	 * Later, snd_rawmidi_transmit_ack() is called.
+	 */
+	memset(port->buf, 0, port->len);
+	port->consume_bytes = port->fill(substream, port->buf);
+	if (port->consume_bytes <= 0) {
+		/* Do it in next chance, immediately. */
+		if (port->consume_bytes == 0)
+			schedule_work(&port->work);
+		return;
+	}
+
+	/* Calculate type of transaction. */
+	if (port->len == 4)
+		type = TCODE_WRITE_QUADLET_REQUEST;
+	else
+		type = TCODE_WRITE_BLOCK_REQUEST;
+
+	/* Start this transaction. */
+	/*
+	 * In Linux FireWire core, when generation is updated with memory
+	 * barrier, node id has already been updated. In this module, After
+	 * this smp_rmb(), load/store instructions to memory are completed.
+	 * Thus, both of generation and node id are available with recent
+	 * values. This is a light-serialization solution to handle bus reset
+	 * events on IEEE 1394 bus.
+	 */
+	generation = port->parent->generation;
+	smp_rmb();
+
+	fw_send_request(port->parent->card, &port->transaction, type,
+			port->parent->node_id, generation,
+			port->parent->max_speed, port->addr,
+			port->buf, port->len, async_midi_port_callback,
+			port);
+}
+
+/**
+ * snd_fw_async_midi_port_init - initialize asynchronous MIDI port structure
+ * @port: the asynchronous MIDI port to initialize
+ * @unit: the target of the asynchronous transaction
+ * @addr: the address to which transactions are transferred
+ * @len: the length of transaction
+ * @fill: the callback function to fill given buffer, and returns the
+ *	       number of consumed bytes for MIDI message.
+ *
+ */
+int snd_fw_async_midi_port_init(struct snd_fw_async_midi_port *port,
+		struct fw_unit *unit, u64 addr, unsigned int len,
+		snd_fw_async_midi_port_fill fill)
+{
+	port->len = DIV_ROUND_UP(len, 4) * 4;
+	port->buf = kzalloc(port->len, GFP_KERNEL);
+	if (port->buf == NULL)
+		return -ENOMEM;
+
+	port->parent = fw_parent_device(unit);
+	port->addr = addr;
+	port->fill = fill;
+
+	INIT_WORK(&port->work, midi_port_work);
+
+	return 0;
+}
+EXPORT_SYMBOL(snd_fw_async_midi_port_init);
+
+/**
+ * snd_fw_async_midi_port_destroy - free asynchronous MIDI port structure
+ * @port: the asynchronous MIDI port structure
+ */
+void snd_fw_async_midi_port_destroy(struct snd_fw_async_midi_port *port)
+{
+	snd_fw_async_midi_port_finish(port);
+	cancel_work_sync(&port->work);
+	kfree(port->buf);
+}
+EXPORT_SYMBOL(snd_fw_async_midi_port_destroy);
+
 MODULE_DESCRIPTION("FireWire audio helper functions");
 MODULE_AUTHOR("Clemens Ladisch <clemens@ladisch.de>");
 MODULE_LICENSE("GPL v2");