[alsa-devel] RFC: Jack-detection control elements on HD-audio

[Takashi Iwai]

At Fri, 19 Jun 2009 10:53:22 +0100,
Mark Brown wrote:
> 
> On Fri, Jun 19, 2009 at 10:04:47AM +0200, Takashi Iwai wrote:
> 
> > yet another thing I've worked recently on is a bit more generalized
> > framework for jack-sense reporting for HD-audio.  This supersedes the
> > existing jack-sense reporting via the input layer.  In addition, it
> > gives the corresponding control elements.
> 
> It'd be nice to keep the input API interface as well - one of the
> reasons I carried on with the existing input interface was that the
> existing userspace stuff I found was using the input API in one way or
> another.  In the embedded space it appears to have often been convenient
> for people to read jack sense from a GPIO as part of a GPIO keyboard
> they're already using which was part of the reason it was never really
> joined up with ALSA in the past.

Don't worry, it's kept as is.  The control elements are just
additions.

Sorry, my wording was unclear.  Let me clarify: the input jack API is
there and used as is now.  What I meant as "supersedes" is that the
code to create and handle the input jack instances in HD-audio driver
is generalized to one and used together with the control API.

> I suspect that which interface is more convenient will depend on what
> the application responding to the events is doing.  For system-wide
> things that aren't focused on audio being able to use the general input
> API makes some sense, while for audio-focused applications that are
> already using ALSA sitting within the ALSA APIs is useful.  This sort of
> system wide thing is probably more common in the embedded space, though
> HAL/DeviceKit do similar things in the desktop space for other kinds of
> hardware.

Right.

> Perhaps rather than superceeding the existing ABI it'd make sense to
> have something in user space as either a plugin or part of the library
> which remaps things into a more ALSA framework?  I confess I've no idea
> what sort of work is involved in doing that; it may be simpler to just
> provide two ABIs.
> 
> > For example, you'll have "Jack HP-Out" (or a bit more verbose like
> > "Jack HP-Out at Ext Rear") control via control API as well as other
> > mixer controls.  This can notify when a jack is plugged/unplugged.
> 
> Including the colours (where reported) is often very helpful for
> figuring out what's what.  The pictures manufacturers seem fond of using
> for describing the jack functions aren't always models of clarity to the
> general user.

Yes, HD-audio spec gives such information, too.

However, the verbose information like a color doesn't fit into the id
string.  A better option would be through the additional TLV like dB
scale.  I just considered but didn't write up yet.


thanks,

Takashi