Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Zipdox]

On 9/17/26 4:23 PM, Zipdox wrote:
> On 9/16/26 8:22 PM, Takashi Iwai wrote:
> > ... or maybe a less cryptic version like below.
> >
> >
> > Takashi
> >
> > -- 8< --
> > diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> > index 33a6a1281410..c6639a45fb24 100644
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -335,6 +335,16 @@ static int get_ctl_value_v1(struct 
> > usb_mixer_elem_info *cval, int request,
> >       return -EINVAL;
> >   }
> > +/* convert the given UAC1 wValue (ICN+1|OCN+1) to UAC2 MCN */
> > +static unsigned int to_mcn(const struct usb_mixer_elem_info *cval,
> > +               unsigned int validx)
> > +{
> > +    unsigned char m = (validx >> 8) & 0xff;
> > +    unsigned char v = validx & 0xff;
> > +
> > +    return (m - 1) * cval->num_outputs * (v - 1);
> > +}
> You used multiplication instead of addition for the last part. I assume 
> this is a mistake? Also you should probably also bitwise and that with 
> 0xFF to make sure it's not more than one byte. The product of the number 
> of input and output channels must be no greater than 256 according to 
> the spec. I don't know if this is checked elsewhere. Other than that it 
> looks good for a patch to get it working. I'll try it out and send a 
> follow-up email shortly.
If you fix the code like this:

static unsigned int to_mcn(const struct usb_mixer_elem_info *cval,
			   unsigned int validx)
{
	unsigned char icn = (validx >> 8) & 0xff;
	unsigned char ocn = validx & 0xff;

	return (icn - 1) * cval->num_outputs + (ocn - 1);
}

then it works correctly. As far as I'm concerned you can merge that 
as-is. It would be good to try on some other hardware as well to check 
for regressions though.