ALSA: usb-audio: Accept multiple protocols in GTBs

It's valid to give different protocols via multiple GTBs; e.g. a MIDI
1.0 port is embedded in a MIDI 2.0 device that talks with MIDI 2.0
protocol.  However, the current driver implementation assumes only a
single protocol over the whole Endpoint, and it can't handle such a
scenario.

This patch changes the driver's behavior to parse GTBs to accept
multiple protocols.  Instead of switching to the last given protocol,
it adds the protocol capability bits now.  Meanwhile, the default
protocol is chosen by the first given protocol in GTBs.

Practically seen, this should be a minor issue, as new devices should
specify the protocols properly via UMP Endpoint Info messages, so this
is rather just covering a corner case.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20240807092303.1935-3-tiwai@suse.de

diff --git a/sound/usb/midi2.c b/sound/usb/midi2.c
index 820d3e4b672ab603b6f2cb91ba95d12b60d519f5..fa655aa4a56ff2e65b7fe2c46ac06f9959e7d9fd 100644 (file)
--- a/sound/usb/midi2.c
+++ b/sound/usb/midi2.c
@@ -607,12 +607,8 @@ static int parse_group_terminal_block(struct snd_usb_midi2_ump *rmidi,
                return 0;
        }
 
-       if (ump->info.protocol && ump->info.protocol != protocol)
-               usb_audio_info(rmidi->umidi->chip,
-                              "Overriding preferred MIDI protocol in GTB %d: %x -> %x\n",
-                              rmidi->usb_block_id, ump->info.protocol,
-                              protocol);
-       ump->info.protocol = protocol;
+       if (!ump->info.protocol)
+               ump->info.protocol = protocol;
 
        protocol_caps = protocol;
        switch (desc->bMIDIProtocol) {
@@ -624,13 +620,7 @@ static int parse_group_terminal_block(struct snd_usb_midi2_ump *rmidi,
                break;
        }
 
-       if (ump->info.protocol_caps && ump->info.protocol_caps != protocol_caps)
-               usb_audio_info(rmidi->umidi->chip,
-                              "Overriding MIDI protocol caps in GTB %d: %x -> %x\n",
-                              rmidi->usb_block_id, ump->info.protocol_caps,
-                              protocol_caps);
-       ump->info.protocol_caps = protocol_caps;
-
+       ump->info.protocol_caps |= protocol_caps;
        return 0;
 }