From: Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH 2/2] ALSA: usb-audio: UAC2 jack detection
Date: Sat, 24 Mar 2018 09:56:05 +0100
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To: Andrew Chant <achant@google.com>
Cc: alsa-devel@alsa-project.org, Ruslan Bilovol <ruslan.bilovol@gmail.com>, Benson Leung <bleung@google.com>

On Fri, 23 Mar 2018 23:24:55 +0100,
Andrew Chant wrote:
> 
> Two new questions:
> #1 - I'd like to report the impedance of the load connected to the jack
> (generally as an integer).  Is a read-only control element the right way to
> do this?

Yes, it would be suitable.

> #2 - In our particular case there's a single jack which can detect presence of
> a microphone and playback separately.  USB descriptors provide a mechanism to
> show that the input and output terminals are linked in this way
> (terminal type 4xx along with bAssocTerminal).
> 
> Is there a better way of having this reported than two separate mono jack
> controls?

This has been discussed in the past.  The current two bool kctls are
the mapping of the former input devices.  One suggestion was to use an
enum for the jack control.  But practically seen this would break
user-space apps, so likely no-go.

I guess we need to live as is -- two bools to represent one
full-duplex jack.


thanks,

Takashi