[alsa-devel] [PATCH] UAC2 clock selector - fixed?

[Louis Gorenfeld]

Hi,
  I'd been struggling with a UAC2 device that I couldn't set the clock on. I finally got in touch with a driver author who pointed me to some official 	documentation (the USB Device Class Definition for Audio Devices). Where the ALSA code always sends a 16-bit packet to control mixer settings, the docs say that the clock selector control uses layout 1 which is 8-bit. By changing the routine to send an 8-bit packet, that control now works.

This is the patch that fixes the problem for me (for ALSA 1.0.25). Is this proper?

--- a/linux-3.4/sound/usb/mixer.c	2012-05-20 15:29:13.000000000 -0700
+++ b/vanilla-3.4/sound/usb/mixer.c	2013-01-02 17:06:11.009660059 -0800
@@ -422,8 +422,13 @@
 	if (cval->mixer->protocol == UAC_VERSION_1) {
 		val_len = cval->val_type >= USB_MIXER_S16 ? 2 : 1;
 	} else { /* UAC_VERSION_2 */
-		/* audio class v2 controls are always 2 bytes in size */
-		val_len = sizeof(__u16);
+		/* audio class v2 controls are often but not always 2 bytes in size */
+		/* For example, the clock selector (see 5.2.5.2.1 in the Universal Serial
+		 * Bus Device Class Definition for Audio Devices document) */
+		if (cval->control == UAC2_CX_CLOCK_SELECTOR)
+			val_len = sizeof(__u8);
+		else
+			val_len = sizeof(__u16);
 
 		/* FIXME */
 		if (request != UAC_SET_CUR) {

Thanks much!
Louis