ALSA: usb-audio: Add a quirk for Plantronics Gamecom 780

Plantronics Gamecom 780 headset has a firmware problem, and when the
FU 0x09 volume is changed, it results in either too loud or silence
except for a very narrow range.  This patch provides a workaround,
ignoring the node, initialize the volume in a sane value and keep
untouched.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=65251
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 0df9ede..ede7536 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -660,6 +660,18 @@
 	return err;
 }
 
+/* quirk for Plantronics GameCom 780 with CM6302 chip */
+static int snd_usb_gamecon780_boot_quirk(struct usb_device *dev)
+{
+	/* set the initial volume and don't change; other values are either
+	 * too loud or silent due to firmware bug (bko#65251)
+	 */
+	u8 buf[2] = { 0x74, 0xdc };
+	return snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0), UAC_SET_CUR,
+			USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_OUT,
+			UAC_FU_VOLUME << 8, 9 << 8, buf, 2);
+}
+
 /*
  * Novation Twitch DJ controller
  */
@@ -986,6 +998,8 @@
 		return snd_usb_nativeinstruments_boot_quirk(dev);
 	case USB_ID(0x0763, 0x2012):  /* M-Audio Fast Track Pro USB */
 		return snd_usb_fasttrackpro_boot_quirk(dev);
+	case USB_ID(0x047f, 0xc010): /* Plantronics Gamecom 780 */
+		return snd_usb_gamecon780_boot_quirk(dev);
 	}
 
 	return 0;