ALSA: usb - For class 2 devices, use channel map from altsettings

The channel config from the streaming descriptor is probably a
better indicator of the channel map than the input terminal.
Use the input terminal's channel map as fallback only.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 3 insertions, 1 deletions

diff --git a/sound/usb/stream.c b/sound/usb/stream.c
index b43b6eec3227..badd1d6d175d 100644
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -587,6 +587,7 @@ int snd_usb_parse_audio_interface(struct snd_usb_audio *chip, int iface_no)
 
                         num_channels = as->bNrChannels;
                         format = le32_to_cpu(as->bmFormats);
+                        chconfig = le32_to_cpu(as->bmChannelConfig);
 
                         /* lookup the terminal associated to this interface
                          * to extract the clock */
@@ -594,7 +595,8 @@ int snd_usb_parse_audio_interface(struct snd_usb_audio *chip, int iface_no)
                                                                             as->bTerminalLink);
                         if (input_term) {
                                 clock = input_term->bCSourceID;
-                                chconfig = le32_to_cpu(input_term->bmChannelConfig);
+                                if (!chconfig && (num_channels == input_term->bNrChannels))
+                                        chconfig = le32_to_cpu(input_term->bmChannelConfig);
                                 break;
                         }