At Wed, 16 Jan 2008 16:19:35 +0100 (CET),
Jaroslav Kysela wrote:
>
> On Wed, 16 Jan 2008, Takashi Iwai wrote:
>
> > At Wed, 16 Jan 2008 15:23:37 +0100 (CET),
> > Jaroslav Kysela wrote:
> > >
> > > Hi,
> > >
> > > I am actually thinking to add TLV support to each PCM stream. The
> > > reason is to obtain various "static" information from the driver without
> > > even opening the PCM stream. The current API lack:
> > >
> > > a) get channel info / name / position (e.g. Front Left Speaker)
> > > - not sure how to handle multichannel cards
> >
> > This won't work with the static TLV because the channel mapping is a
> > dynamic information. It varies depending on the hw_params setting.
> > A typical difference is the mappings between 4 and 6 channels
> > (FL/FR/RL/RR and FL/FR/C/LFE/RL/RR).
> >
> > > - I'm sure that this is something to be user configurable
> >
> > Everything is user-configurable :)
> >
> > But the channel mapping is basically bound to the driver
> > implementation, so rather there is no real user-configuration, AFAIK.
> >
> > I've already hacked to extend channel_info to include this
> > information. If you're interested, I'll post patches.
> >
> > > b) get possible channels
> > > c) get possible formats
> >
> > These *could* be dynamic, too. That's why we have a complex hw_params
> > procedure. But, they are static for most cases, so it would likely
> > work.
>
> Ok, I didn't explain the term "static" as well. I think that the best way
> might be to group parameters like:
>
> parameters #1 {
> channels {
> 2 { FL, FR }
> 4 { FL, FR, RL, RR }
> 6 { FL, FR, C, LFE, RL, RR }
> }
> formats {
> S16_LE, S32_LE
> }
> }
> parameters #2 {
> ....
> }
>
> Just idea. We can get this change as base to change from refine method to
> provide a list of possible values method and reduce the kernel and
> alsa-lib code.
This looks promising. The similar mechanism is already in USB-audio
and HD-audio protocols, and it's confirmed to work in most cases, so
far.
> > > d) various inter-PCM-device constraint description (e.g. if S/PDIF
> > > PCM stream can be used with analog etc.)
> >
> > This sounds good. Any practical use in mind?
>
> I think that Lennart Poettering requirested this and I think that it might
> make sense for various TV Linux boxes ;-)
Of course, PA would need such every detailed h/w information! ;)
Takashi
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