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

[Zipdox <zipdox@zipdox.net>]

On 9/17/26 6:15 PM, Takashi Iwai wrote:
> Good to hear.  If you have a chance to test my last series of patches,
> it'd be appreciated.
> 
> BTW, I'll be off from tomorrow, and the issue is no new bug to be
> urgently fixed, so I'll handle after back to work again :)
> 
> 
> thanks,
> 
> Takashi

I have compiled your patches and the mixer unit control seems to work 
correctly.

Another thing on my mind is the following section from section 5.2.5.5.1 
from the spec:
> A Mixer Unit consists of a number of Mixer Controls, either programmable or fixed. A Mixer Control must
> support the CUR and RANGE(MIN, MAX, RES) attributes. The settings for the CUR, MIN, and MAX
> attributes can range from +127.9961 dB (0x7FFF) down to -127.9961 dB (0x8001) in steps of 1/256 dB or
> 0.00390625 dB (0x0001). The settings for the RES attribute can only have positive values and range from
> 1/256 dB (0x0001) to +127.9961 dB (0x7FFF).
> In addition, code 0x8000, representing silence (i.e., -∞ dB), must always be implemented. However, it must
> never be reported as the MIN attribute value.

Is this presently handled? For reference, 0x8000 is -32768. When I use 
qasmixer or alsamixer, for example, it only goes down to -32767. This is 
the same in UAC1 by the way. Should we add a mute control to mixer 
nodes? Or perhaps extend the reported range downward by one, and 
overwrite the lowest value to -32768 when writing to a mixer unit. The 
latter is my preferred solution.