[alsa-devel] TLV support for PCM (in driver)
tiwai at suse.de
Wed Jan 16 15:49:20 CET 2008
At Wed, 16 Jan 2008 15:23:37 +0100 (CET),
Jaroslav Kysela wrote:
> 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
> 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?
> e) eventually more information for device name hinting for userspace
> (current problems for HDA, AC97, USB devices are that we have only one
> .conf file per driver covering all hardware - we need to detect real
> device capabilities and show only devices which can be really used)
This would be helpful, too.
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