[alsa-devel] ASoC audio fabric OF bindings RFC. was: Re: ASoC MPC5xxx PSC AC97 audio driver

[Mark Brown]

On Mon, Sep 12, 2011 at 08:31:58AM +0200, David Jander wrote:
> Mark Brown <broonie at opensource.wolfsonmicro.com> wrote:

> > This isn't really something that should go into device tree, ALSA is a
> > Linux specific concept.

> There are many Linux-specific details in Linux's implementation of Open
> Firmware Device Trees. Right now, thanks to Linux, Open-Firmware device trees

This is generally considered a bug in the bindings, the bindings are for
cross-platform usage and should not be specific to any OS.

> introduced in arch/arm right now. On all these platforms, its sole existence
> is purely for running Linux with minimal board support code in the kernel.

Other OSs are actively using device tree.

> So, why not add a few more Linux-specific bits to it, if it helps get rid of
> the last bit of board-specific code?

Eliminating board specific code for audio is not a realistic goal, the
configuration of modern audio subsystems is too complex and dynamic.  It
is realistic to make machine drivers which cover broad classes of
devices with similar hardware.

> The platforms that will use those bindings, will never have
> Open-Firmware bioses in the first place, and their DT sources will be part of
> the kernel source tree anyway.

The plan is to push the device trees out of the kernel into a separate
repository.

> > What we should really be doing here is to autodiscover by reading the ID
> > registers in the device.  That needs generic AC'97 bus work which we
> > don't have right now.

> Seems reasonable, but is correct autodiscovery really possible for all
> configurations and all DAI-codec combinations?

Yes, it's a very basic part of AC'97.