[alsa-devel] Channel map API patches: to be 3.7 or not to be?

[Raymond Yau]

2012-9-11 下午8:14 於 "Takashi Iwai" <tiwai at suse.de> 寫道：
>
> At Tue, 11 Sep 2012 10:22:23 +0200,
> Takashi Iwai wrote:
> >
> > At Tue, 11 Sep 2012 16:10:43 +0800,
> > Raymond Yau wrote:
> > >
> > > 2012-9-11 上午1:43 於 "Takashi Iwai" <tiwai at suse.de> 寫道：
> > > >
> > > > Hi,
> > > >
> > > > does anyone have concern if I push the current channel map API
patches
> > > > (in sound-unstable git tree topic/tlv-chmap branch) for linux-next,
> > > > i.e. for inclusion to 3.7 kernel?
> > > >
> > > > I don't worry too much about the kernel API.  This can be refactored
> > > > later.  But the kernel ABI must retain, so we won't change in an
> > > > incompatible way any longer once after it's merged to the upstream.
> > > >
> > > > So, if anyone sees a flaw in the kernel ABI definition using control
> > > > elements, let me know.
> > > >
> > > > (But note that the API can't be perfect for all generic purposes.
> > > >  It's designed to be "good enough" for a big lack for multi-channel
> > > >  streaming.  Of course, this doesn't discourage to use the API for
any
> > > >  other purposes.)
> > > >
> > >
> > > How about the channel map of the usb mono playback device and those
sound
> > > card which can pan mono to stereo speakers and headphone?
> >
> > If the device specifies which speaker position the mono channel is
> > for, then you can map it properly.  Unless it's really specified by
> > the device, the mono stream is UNKNOWN position in general.
>
> BTW, this reminds me of an open question:
>   is it useful to add SND_CHMAP_MONO, or is it just redundant?
>
> It's nothing but indicating a mono channel without any channel
> position, so I supposed SND_CHMAP_UNKNOWN being sufficient.  OTOH,
> SND_CHMAP_MONO would give a clear sign of mono streams while
> SND_CHMAP_UNKNOWN could be used for any other exceptional purposes.
>
>

How about those sound card which use multi plugin for multi channels (e.g.
emu10k1 , c0106 and cs4630) as they can also provide a rear or clfe device
for independent stereo playback ?

It seem the branch still miss the patch for au88x0 and ymfpci which need to
check the sdac bit of ac97 codec for adding the 4 channels map

Most of 2.1 external speaker set only have green jack and those creative
4.1 fps have green and black jacks where the volume of subwoofer is
controlled by the volume knob of the subwoofer

https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/1047543

However some of those 2.1 internal speaker in notebook may need stereo
channel map (e.g. stac920x hda codec using mono widget)

Some notebook (e.g. acer aspire 4930g) hda codec) may need a special
channel map for the internal 2.1 speaker but a stereo channel map for the
external 2.1 speaker and some Asus laptops have propertiary jack for the
external subwoofer

http://git.kernel.org/?p=linux/kernel/git/tiwai/sound.git;a=commit;h=786c51f9168cfd2d49250c6e5e60035cbb2fd5a1

Does those 3stack-6ch laptop/desktop have those 5.1 channel map before the
input jack retasked as output?

If yes, does the retasking is performed automatically by the set channel
map function?

http://git.kernel.org/?p=linux/kernel/git/tiwai/sound-unstable.git;a=commit;h=9c9a5175e65b2667001e6a3b6dedddebeee82aa2