ALSA: usb-audio: Support multiple control interfaces

Registering Numark Party Mix II fails with error 'bogus bTerminalLink 1'.
The problem stems from the driver not being able to find input/output
terminals required to configure audio streaming. The information about
those terminals is stored in AudioControl Interface. Numark device
contains 2 AudioControl Interfaces and the driver checks only one of them.

According to the USB standard, a device can have multiple audio functions,
each represented by Audio Interface Collection. Every audio function is
considered to be closed box and will contain unique AudioControl Interface
and zero or more AudioStreaming and MIDIStreaming Interfaces.

The Numark device adheres to the standard and defines two audio functions:
- MIDIStreaming function
- AudioStreaming function
It starts with MIDI function, followed by the audio function. The driver
saves the first AudioControl Interface in `snd_usb_audio` structure
associated with the entire device. It then attempts to use this interface
to query for terminals and clocks. However, this fails because the correct
information is stored in the second AudioControl Interface, defined in the
second Audio Interface Collection.

This patch introduces a structure holding association between each
MIDI/Audio Interface and its corresponding AudioControl Interface,
instead of relying on AudioControl Interface defined for the entire
device. This structure is populated during usb probing phase and leveraged
later when querying for terminals and when sending USB requests.

Alternative solutions considered include:
- defining a quirk for Numark where the order of interface is manually
changed, or terminals are hardcoded in the driver. This solution would
have fixed only this model, though it seems that device is USB compliant,
and it also seems that other devices from this company may be affected.
What's more, it looks like products from other manufacturers have similar
problems, i.e. Rane One DJ console
- keeping a list of all AudioControl Interfaces and querying all of them
to find required information. That would have solved my problem and have
low probability of breaking other devices, as we would always start with
the same logic of querying first AudioControl Interface. This solution
would not have followed the standard though.

This patch preserves the `snd_usb_audio.ctrl_intf` variable, which holds
the first AudioControl Interface, and uses it as a fallback when some
interfaces are not parsed correctly and lack an associated AudioControl
Interface, i.e., when configured via quirks.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=217865
Signed-off-by: Karol Kosik <k.kosik@outlook.com>
Link: https://patch.msgid.link/AS8P190MB1285893F4735C8B32AD3886BEC852@AS8P190MB1285.EURP190.PROD.OUTLOOK.COM
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 12 insertions, 0 deletions

diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 43d4029edab4..b0f042c99608 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -21,6 +21,15 @@ struct media_intf_devnode;
 
 #define MAX_CARD_INTERFACES	16
 
+/*
+ * Structure holding assosiation between Audio Control Interface
+ * and given Streaming or Midi Interface.
+ */
+struct snd_intf_to_ctrl {
+	u8 interface;
+	struct usb_host_interface *ctrl_intf;
+};
+
 struct snd_usb_audio {
 	int index;
 	struct usb_device *dev;
@@ -63,6 +72,9 @@ struct snd_usb_audio {
 	struct usb_host_interface *ctrl_intf;	/* the audio control interface */
 	struct media_device *media_dev;
 	struct media_intf_devnode *ctl_intf_media_devnode;
+
+	unsigned int num_intf_to_ctrl;
+	struct snd_intf_to_ctrl intf_to_ctrl[MAX_CARD_INTERFACES];
 };
 
 #define USB_AUDIO_IFACE_UNUSED	((void *)-1L)