ALSA: usb-audio: add Starr Labs USB MIDI support

Add support for Starr Labs USB MIDI devices such as the Z7S, which are
based on an FTDI serial UART chip.

Based on a patch by Daniel Mack.

Signed-off-by: Kristian Amlie <kristian@amlie.name>
Acked-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 27 insertions, 0 deletions

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index f9289102886a..e21f026d9577 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -816,6 +816,22 @@ static struct usb_protocol_ops snd_usbmidi_raw_ops = {
         .output = snd_usbmidi_raw_output,
 };
 
+/*
+ * FTDI protocol: raw MIDI bytes, but input packets have two modem status bytes.
+ */
+
+static void snd_usbmidi_ftdi_input(struct snd_usb_midi_in_endpoint* ep,
+                                   uint8_t* buffer, int buffer_length)
+{
+        if (buffer_length > 2)
+                snd_usbmidi_input_data(ep, 0, buffer + 2, buffer_length - 2);
+}
+
+static struct usb_protocol_ops snd_usbmidi_ftdi_ops = {
+        .input = snd_usbmidi_ftdi_input,
+        .output = snd_usbmidi_raw_output,
+};
+
 static void snd_usbmidi_us122l_input(struct snd_usb_midi_in_endpoint *ep,
                                      uint8_t *buffer, int buffer_length)
 {
@@ -2163,6 +2179,17 @@ int snd_usbmidi_create(struct snd_card *card,
                 /* endpoint 1 is input-only */
                 endpoints[1].out_cables = 0;
                 break;
+        case QUIRK_MIDI_FTDI:
+                umidi->usb_protocol_ops = &snd_usbmidi_ftdi_ops;
+
+                /* set baud rate to 31250 (48 MHz / 16 / 96) */
+                err = usb_control_msg(umidi->dev, usb_sndctrlpipe(umidi->dev, 0),
+                                      3, 0x40, 0x60, 0, NULL, 0, 1000);
+                if (err < 0)
+                        break;
+
+                err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
+                break;
         default:
                 snd_printd(KERN_ERR "invalid quirk type %d\n", quirk->type);
                 err = -ENXIO;