ALSA: oxfw: copy handlers of asynchronous transaction for MIDI capture

This commit copies some functions of asynchronous transactions for MIDI
capture, to merge scs1x module. The features of payload in asynchronous
transaction are:

 * System exclusive messages for SCS.1 are encoded without ID data. In
   this encoding scheme, 4 bits in LSB are available. The bits are squashed
   in payload byte. Thus, one payload byte transfers two MIDI messages.
 * The first byte of payload byte means:
  * 0x00: depending on second payload byte
   * 0xf9: including escaped system exclusive messages for SCS.1, up to
     3 byte (= 6 MIDI messages)
   * the others: including MIDI 1.0 messages
  * the others: including escaped system exclusive messages for SCS.1, up
    to 64 bytes

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

sound/firewire/oxfw/oxfw-scs1x.c

@@ -11,18 +11,99 @@
 
 #define HSS1394_ADDRESS			0xc007dedadadaULL
 #define HSS1394_MAX_PACKET_SIZE		64
+#define HSS1394_TAG_USER_DATA		0x00
 #define HSS1394_TAG_CHANGE_ADDRESS	0xf1
 
 struct fw_scs1x {
 	struct fw_address_handler hss_handler;
+	u8 input_escape_count;
+	struct snd_rawmidi_substream *input;
 };
 
+static const u8 sysex_escape_prefix[] = {
+	0xf0,			/* SysEx begin */
+	0x00, 0x01, 0x60,	/* Stanton DJ */
+	0x48, 0x53, 0x53,	/* "HSS" */
+};
+
+static void midi_input_escaped_byte(struct snd_rawmidi_substream *stream,
+				    u8 byte)
+{
+	u8 nibbles[2];
+
+	nibbles[0] = byte >> 4;
+	nibbles[1] = byte & 0x0f;
+	snd_rawmidi_receive(stream, nibbles, 2);
+}
+
+static void midi_input_byte(struct fw_scs1x *scs,
+			    struct snd_rawmidi_substream *stream, u8 byte)
+{
+	const u8 eox = 0xf7;
+
+	if (scs->input_escape_count > 0) {
+		midi_input_escaped_byte(stream, byte);
+		scs->input_escape_count--;
+		if (scs->input_escape_count == 0)
+			snd_rawmidi_receive(stream, &eox, sizeof(eox));
+	} else if (byte == 0xf9) {
+		snd_rawmidi_receive(stream, sysex_escape_prefix,
+				    ARRAY_SIZE(sysex_escape_prefix));
+		midi_input_escaped_byte(stream, 0x00);
+		midi_input_escaped_byte(stream, 0xf9);
+		scs->input_escape_count = 3;
+	} else {
+		snd_rawmidi_receive(stream, &byte, 1);
+	}
+}
+
+static void midi_input_packet(struct fw_scs1x *scs,
+			      struct snd_rawmidi_substream *stream,
+			      const u8 *data, unsigned int bytes)
+{
+	unsigned int i;
+	const u8 eox = 0xf7;
+
+	if (data[0] == HSS1394_TAG_USER_DATA) {
+		for (i = 1; i < bytes; ++i)
+			midi_input_byte(scs, stream, data[i]);
+	} else {
+		snd_rawmidi_receive(stream, sysex_escape_prefix,
+				    ARRAY_SIZE(sysex_escape_prefix));
+		for (i = 0; i < bytes; ++i)
+			midi_input_escaped_byte(stream, data[i]);
+		snd_rawmidi_receive(stream, &eox, sizeof(eox));
+	}
+}
+
 static void handle_hss(struct fw_card *card, struct fw_request *request,
 		       int tcode, int destination, int source, int generation,
 		       unsigned long long offset, void *data, size_t length,
 		       void *callback_data)
 {
-	fw_send_response(card, request, RCODE_COMPLETE);
+	struct fw_scs1x *scs = callback_data;
+	struct snd_rawmidi_substream *stream;
+	int rcode;
+
+	if (offset != scs->hss_handler.offset) {
+		rcode = RCODE_ADDRESS_ERROR;
+		goto end;
+	}
+	if (tcode != TCODE_WRITE_QUADLET_REQUEST &&
+	    tcode != TCODE_WRITE_BLOCK_REQUEST) {
+		rcode = RCODE_TYPE_ERROR;
+		goto end;
+	}
+
+	if (length >= 1) {
+		stream = ACCESS_ONCE(scs->input);
+		if (stream)
+			midi_input_packet(scs, stream, data, length);
+	}
+
+	rcode = RCODE_COMPLETE;
+end:
+	fw_send_response(card, request, rcode);
 }
 
 static int register_address(struct snd_oxfw *oxfw)