[alsa-devel] Mixer regression with usb soundcard

[Takashi Iwai]

On Mon, 18 Dec 2017 17:59:38 +0100,
Jaejoong Kim wrote:
> 
> AudioControl Interface Descriptor:
>         bLength                 8
>         bDescriptorType        36
>         bDescriptorSubtype      5 (SELECTOR_UNIT)
>         bUnitID                11
>         bNrInPins               2
>         baSource( 0)           14
>         baSource( 1)            5
>         iSelector               0
>         ^^^^^^^^^
> 
> >From the lsusb.txt, iSelector is '0' which means
> uac_selector_unit_iSelector() return zero I think.

Yes, and in that case, nameid=0, thus it should go to
get_term_name(), and there must be no difference.
If any difference came from the given commit, it must be nameid!=0,
and yet snd_usb_copy_string_desc(namei) returns an error.

In anyway, another potential fix would be the patch like below.
It covers the case where an error is returned from
snb_usb_copy_string_desc() and doesn't fall back to the default name
resolution.


thanks,

Takashi

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -656,10 +656,14 @@ static int get_term_name(struct mixer_build *state, struct usb_audio_term *iterm
 			 unsigned char *name, int maxlen, int term_only)
 {
 	struct iterm_name_combo *names;
+	int len;
 
-	if (iterm->name)
-		return snd_usb_copy_string_desc(state, iterm->name,
+	if (iterm->name) {
+		len = snd_usb_copy_string_desc(state, iterm->name,
 						name, maxlen);
+		if (len)
+			return len;
+	}
 
 	/* virtual type - not a real terminal */
 	if (iterm->type >> 16) {