[ALSA] usb-audio: work around broken M-Audio MidiSport Uno firmware

The firmware of the M-Audio USB Uno MIDI Interface has, at least in
hardware revision 1.25, a bug that garbles its USB output.  When it
receives a Note On MIDI message that uses running status, the resulting
USB MIDI packet has a wrong CIN (4 instead of 9) and a wrong length
(2 bytes, the status byte is still missing).
This patch adds a workaround to track the CINs and the MIDI messages of
received USB MIDI packets to detect whether a packet with CIN 4 is a
correct SysEx packet or a buggy running status packet.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

1 files changed, 51 insertions, 1 deletions

diff --git a/sound/usb/usbmidi.c b/sound/usb/usbmidi.c
index 24f5a26c5f0c..911f4482b5e1 100644
--- a/sound/usb/usbmidi.c
+++ b/sound/usb/usbmidi.c
@@ -1,7 +1,7 @@
 /*
  * usbmidi.c - ALSA USB MIDI driver
  *
- * Copyright (c) 2002-2005 Clemens Ladisch
+ * Copyright (c) 2002-2007 Clemens Ladisch
  * All rights reserved.
  *
  * Based on the OSS usb-midi driver by NAGANO Daisuke,
@@ -145,6 +145,7 @@ struct snd_usb_midi_in_endpoint {
         struct urb* urb;
         struct usbmidi_in_port {
                 struct snd_rawmidi_substream *substream;
+                u8 running_status_length;
         } ports[0x10];
         u8 seen_f5;
         u8 error_resubmit;
@@ -366,6 +367,46 @@ static void snd_usbmidi_midiman_input(struct snd_usb_midi_in_endpoint* ep,
 }
 
 /*
+ * Buggy M-Audio device: running status on input results in a packet that has
+ * the data bytes but not the status byte and that is marked with CIN 4.
+ */
+static void snd_usbmidi_maudio_broken_running_status_input(
+                                        struct snd_usb_midi_in_endpoint* ep,
+                                        uint8_t* buffer, int buffer_length)
+{
+        int i;
+
+        for (i = 0; i + 3 < buffer_length; i += 4)
+                if (buffer[i] != 0) {
+                        int cable = buffer[i] >> 4;
+                        u8 cin = buffer[i] & 0x0f;
+                        struct usbmidi_in_port *port = &ep->ports[cable];
+                        int length;
+                        
+                        length = snd_usbmidi_cin_length[cin];
+                        if (cin == 0xf && buffer[i + 1] >= 0xf8)
+                                ; /* realtime msg: no running status change */
+                        else if (cin >= 0x8 && cin <= 0xe)
+                                /* channel msg */
+                                port->running_status_length = length - 1;
+                        else if (cin == 0x4 &&
+                                 port->running_status_length != 0 &&
+                                 buffer[i + 1] < 0x80)
+                                /* CIN 4 that is not a SysEx */
+                                length = port->running_status_length;
+                        else
+                                /*
+                                 * All other msgs cannot begin running status.
+                                 * (A channel msg sent as two or three CIN 0xF
+                                 * packets could in theory, but this device
+                                 * doesn't use this format.)
+                                 */
+                                port->running_status_length = 0;
+                        snd_usbmidi_input_data(ep, cable, &buffer[i + 1], length);
+                }
+}
+
+/*
  * Adds one USB MIDI packet to the output buffer.
  */
 static void snd_usbmidi_output_standard_packet(struct urb* urb, uint8_t p0,
@@ -525,6 +566,12 @@ static struct usb_protocol_ops snd_usbmidi_midiman_ops = {
         .output_packet = snd_usbmidi_output_midiman_packet,
 };
 
+static struct usb_protocol_ops snd_usbmidi_maudio_broken_running_status_ops = {
+        .input = snd_usbmidi_maudio_broken_running_status_input,
+        .output = snd_usbmidi_standard_output, 
+        .output_packet = snd_usbmidi_output_standard_packet,
+};
+
 /*
  * Novation USB MIDI protocol: number of data bytes is in the first byte
  * (when receiving) (+1!) or in the second byte (when sending); data begins
@@ -1606,6 +1653,9 @@ int snd_usb_create_midi_interface(struct snd_usb_audio* chip,
         switch (quirk ? quirk->type : QUIRK_MIDI_STANDARD_INTERFACE) {
         case QUIRK_MIDI_STANDARD_INTERFACE:
                 err = snd_usbmidi_get_ms_info(umidi, endpoints);
+                if (chip->usb_id == USB_ID(0x0763, 0x0150)) /* M-Audio Uno */
+                        umidi->usb_protocol_ops =
+                                &snd_usbmidi_maudio_broken_running_status_ops;
                 break;
         case QUIRK_MIDI_FIXED_ENDPOINT:
                 memcpy(&endpoints[0], quirk->data,