[alsa-devel] Jack reporting v2

[Takashi Iwai]

At Tue, 3 Jun 2008 11:40:48 +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 also feel uneasy that it's built in unconditionally and requires an 
additional dependency on CONFIG_INPUT.  The fact that both SND and
INPUT can be modules makes things a bit complicated.

As a workaround, how about to select with "if" conditions?
For example, in sound/core/Kconfig,

config SND_JACK
	bool

while the driver requires SND_JACK has the below:

config SND_FOO
	tristate "..."
	...
	select SND_JACK if INPUT=y || INPUT=SND

Yeah, it looks horrible at a first glance, but it's a known workaround
for reverse selections...

In sound/core/Makefile, just add the line:

snd-$(CONFIG_SND_JACK) += jack.o

so that the code is built into snd module only when necessary.

Also, sound/jack.h should provide empty inline functions for the case 
CONFIG_SND_JACK=n.  Then you'll be able to reduce ifdefs in the driver
codes.


thanks,

Takashi