[pulseaudio-discuss] [PATCH] alsa-mixer: Don't let "Mic Jack Mode" alone create a "Line In" path

[David Henningsson]

On 10/17/2012 02:46 PM, Tanu Kaskinen wrote:
> On Tue, 2012-10-16 at 11:49 +0200, David Henningsson wrote:
>> The IDT/Sigmatel codec driver often creates a "Mic Jack Mode" for
>> every mic jack, so it can change functionality between Mic and Line In.
>>
>> However, as the "Mic Jack" is the standard naming, our current solution
>> does not make the Line In port unavailable when nothing is plugged in.
>>
>> This patch makes the "Line In" port not to be created just because there
>> is a "Mic Jack Mode" that could be set to "Line". This makes the behaviour
>> consistent with e g "Dock Mic Jack Mode", "Front Mic Jack Mode" etc, where
>> we don't create a "Dock Line" or "Dock Mic" port either.
>
> Do you know if the "Mic Jack Mode" element actually does something (e.g.
> toggle some amplifier)? If there's a difference between the modes, it
> would seem like a good thing to have both "Mic" and "Line" ports.
> Pulseaudio should then somehow understand that the Mic Jack makes both
> ports available or unavailable...
>
> If the element doesn't do anything, then removing one of the ports is of
> course just fine (naming the port to "Mic / Line In" would be nice,
> though).

Yes, setting "Mic Jack Mode" to "Line" would turn of the VREF pin of the 
codec, i e, the phantom power to the microphone. In "Mic" mode there's 
usually a phantom power of 80% of Vdd. (I have never actually measured 
this - I'm just looking at the HDA spec.)

So my argument is more about confusion ("Hey, PulseAudio says I've got a 
line in port, but I don't have one, let's file a bug!").


-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic