Control interconnection information API?

Control interconnection information API?

[Eliot Blennerhassett]

New Year's Greetings,


something that seems to be lacking in the ALSA API, or at least the way
of describing controls (by name only), is any concept of the
connectivity between the various controls and the codecs and output
terminals.

One use for such information is to build a GUI that shows this
connectivity (instead of the current bucket'o'controls approach).

Now there are a couple of special cases:

* HDA driver exports the codec widget information via a proc file,
allowing the codecgraph tool to visualise the connections.
Widgets have numeric IDs and list the IDs of widgets that connect to
their inputs.

* ASoC DAPM (which I (not being an ASoC developer or user) have mostly
been skimming over in this list).

Reading this
http://www.mjmwired.net/kernel/Documentation/sound/alsa/soc/dapm.txt
3. Codec Widget Interconnections. I can see that there are lists of
connections.  I'm not sure if these are visible to userspace via any API?


So:
Can either of these schemes be generalised to all ALSA drivers?
Is there some other way to reveal the information (Connections TLV, new
API etc?)
Does anybody else thing this is worth pursuing, or is it just me?


regards

--
Eliot Blennerhassett
AudioScience Inc

Re: Control interconnection information API?

[Mark Brown]

On Thu, Jan 01, 2009 at 12:01:47PM +1300, Eliot Blennerhassett wrote:

> * ASoC DAPM (which I (not being an ASoC developer or user) have mostly
> been skimming over in this list).

> Reading this
> http://www.mjmwired.net/kernel/Documentation/sound/alsa/soc/dapm.txt
> 3. Codec Widget Interconnections. I can see that there are lists of
> connections.  I'm not sure if these are visible to userspace via any API?

These are not visible to user space and the information provided is not
at all complete - as well as DAPM controls (used for power management)
most devices will also have a number of regular ALSA controls which
aren't tied in with the path information yet.  It's been at the back of
my mind to let drivers do that but it's not particularly near the top of
my list.

> Can either of these schemes be generalised to all ALSA drivers?
> Is there some other way to reveal the information (Connections TLV, new
> API etc?)

Anything that works for ASoC should be able to work for all ALSA
drivers, though since there's nothing there yet it's probably not
particularly useful for you right now.

> Does anybody else thing this is worth pursuing, or is it just me?

Yes, it'd definitely be useful for ASoC.  One of the issues with ASoC at
the minute is that embedded codecs (especially audio hub codecs) can
have a very large number of controls and having the interconnection
information availiable in mixer user interfaces would help users work
with them.

Even with just the existing power information it'd still be a win.