Re: [alsa-devel] [PATCH v2] ALSA: usb-audio: Add support for Akai MPC Element USB MIDI controller

9 Jan 2015


      Paul Bonser wrote:
...
On 01/08/2015 03:56 PM, Clemens Ladisch wrote:
...
Paul Bonser wrote:
...
The Akai MPC Element incorrectly reports its bInterfaceClass as 255, but
otherwise implements the USB MIDI spec correctly.
This adds a quirks-table.h entry which allows the device to be
recognized as a standard USB MIDI device.
+++ b/sound/usb/quirks-table.h
+{

/* Akai MPC Element */
USB_DEVICE(0x09e8, 0x0021),
.driver_info = (unsigned long) & (const struct snd_usb_audio_quirk) {
.ifnum = QUIRK_ANY_INTERFACE,


.type = QUIRK_COMPOSITE,


.data = & (const struct snd_usb_audio_quirk[]) {


	{


		.ifnum = 0,


		.type = QUIRK_IGNORE_INTERFACE


	},


	{


		.ifnum = 1,


		.type = QUIRK_MIDI_STANDARD_INTERFACE


	},


	{


		.ifnum = -1


	}


}


}

+},
Why a composite quirk?  Does a single quirk entry not work?
A single quirk entry results in an error message in dmesg:
"snd-usb-audio: probe of 3-2:1.0 failed with error -5"
That message is normal for unhandled interfaces.
Does it actually prevent the device from working?
Regards,
Clemens