[alsa-devel] [PATCH] UAC2 clock selector - fixed?
Louis Gorenfeld
louis at museresearch.com
Thu Jan 3 02:01:41 CET 2013
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
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