[alsa-devel] Jack reporting v2

Dmitry Torokhov dmitry.torokhov at gmail.com
Tue Jun 3 17:17:26 CEST 2008

Hi Mark,

On Tue, Jun 03, 2008 at 11:40:48AM +0100, Mark Brown wrote:
> The following couple of patches update the jack reporting API I posted
> last week with the feedback I have received so far.  The changes since
> the last submision are:
>  - Addition of snd_jack_set_parent(), allowing drivers to override the
>    default parent for the input device prior to registration.
>  - The jack detection support is now included unconditionally in ALSA,
>    requiring a dependency on the input subsystem.
> I'm not entirely happy with making ALSA depend on input but given that
> it is only optional on embedded systems and that the input core is not
> that large it seemed the best way of ensuring that the input subsystem
> is available for the jack API without hassle for drivers using it,
> especially given the lack of dependency propagation from select.

I think it is a great idea to intoroduce a mechanism treporting state
of a generic connector, it was a long overdue. However I don't think
that using input as a delivery mechanism is the best solution. What is
needed from a connector:

1. A way to query its state
2. A way to notify userspace of state change.

Pros for using input devices:
- we already have them

- space consideration. Input_dev structure is quite fat. It has all
  the capabilities strings exported through sysfs, hist of other
  attributes, etc. On top of that we have a character device (evdev)
  plus its own sysfs representation. IOW lots of stuff.
- input device require ioctl to get the switch state, no easy way to
  do it through sysfs.
- As the number of types of connectors grows new switches will need to
  be added to input, potentially completely unrelated. My lacmus test
  for it - does it make sense to add network cable state to inputi

Do you think that something small that has only one sysfs device per
switch and uses KOBJ_ONLINE/KOBJ_OFFLINE to signal state change would
be better suited here?

BTW, the same goes for the SW_DOCK that Matthew wants to add (CC-ed).


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