[alsa-devel] Multiple channels mapping
Hi,
The DSP I am working on supports channel assignments similar to ALSA route plug-in described in this link http://drona.csa.iisc.ernet.in /~uday/alsamch.shtml. I am currently looking a way to pass channel/speaker mapping information of PCM stream( i.c channel 0 -> Front Left speaker, channel 1 -> Front Right speaker) to ALSA driver. I looked at latest kernel tree and don't think there is already provision for my purpose. Can anyone confirm? If I were to improvise a way to pass channel/speaker mapping information, should I follow the same approach similar to how bits per sample and other hardware parameter is passed?
Thanks Patrick
At Tue, 07 Feb 2012 17:02:00 -0800, Patrick Lai wrote:
Hi,
The DSP I am working on supports channel assignments similar to ALSA route plug-in described in this link http://drona.csa.iisc.ernet.in /~uday/alsamch.shtml. I am currently looking a way to pass channel/speaker mapping information of PCM stream( i.c channel 0 -> Front Left speaker, channel 1 -> Front Right speaker) to ALSA driver. I looked at latest kernel tree and don't think there is already provision for my purpose. Can anyone confirm? If I were to improvise a way to pass channel/speaker mapping information, should I follow the same approach similar to how bits per sample and other hardware parameter is passed?
Currently the channel-mapping information is a missing piece in ALSA framework, and it's a very long-standing item on my TODO list.
The implementation itself should be easy, but the only question is the API design. If you have a good proposal, please speak up.
thanks,
Takashi
Takashi Iwai wrote:
Currently the channel-mapping information is a missing piece in ALSA framework, and it's a very long-standing item on my TODO list.
The implementation itself should be easy, but the only question is the API design. If you have a good proposal, please speak up.
TLVs on media controller entities.
I really should complete those patches ...
Regards, Clemens
At Wed, 08 Feb 2012 10:18:29 +0100, Clemens Ladisch wrote:
Takashi Iwai wrote:
Currently the channel-mapping information is a missing piece in ALSA framework, and it's a very long-standing item on my TODO list.
The implementation itself should be easy, but the only question is the API design. If you have a good proposal, please speak up.
TLVs on media controller entities.
Well, my concern is that it might be too far from the other PCM stuff. How the implementation would look like?
BTW, the channel-mapping info can be useful for the automatic plug layer, too. It would re-route the channels when not following ALSA-standard maps automatically, for example. (Remember some old AC97 chips.)
More question is whether this information should be available before or after hw_params setup.
thanks,
Takashi
Takashi Iwai wrote:
Clemens Ladisch wrote:
Takashi Iwai wrote:
Currently the channel-mapping information is a missing piece in ALSA framework, and it's a very long-standing item on my TODO list.
The implementation itself should be easy, but the only question is the API design. If you have a good proposal, please speak up.
TLVs on media controller entities.
Well, my concern is that it might be too far from the other PCM stuff. How the implementation would look like?
There is one media controller device node per device (= ALSA card), containing multiple entities (similar to how a ctl device contains multiple controls). /dev/media42 _is_ separate, but the entity that represents a PCM device is handled by the PCM code, so it would be possible to have a shortcut to get a PCM device's TLVs directly.
More question is whether this information should be available before or after hw_params setup.
This is pretty much static information, which is available even when the PCM device isn't opened.
BTW, the channel-mapping info can be useful for the automatic plug layer, too.
And if there is a need for channel mapping information of ALSA plugins, there needs to be a userspace library for the media controller API.
Regards, Clemens
At Wed, 08 Feb 2012 12:32:17 +0100, Clemens Ladisch wrote:
Takashi Iwai wrote:
Clemens Ladisch wrote:
Takashi Iwai wrote:
Currently the channel-mapping information is a missing piece in ALSA framework, and it's a very long-standing item on my TODO list.
The implementation itself should be easy, but the only question is the API design. If you have a good proposal, please speak up.
TLVs on media controller entities.
Well, my concern is that it might be too far from the other PCM stuff. How the implementation would look like?
There is one media controller device node per device (= ALSA card), containing multiple entities (similar to how a ctl device contains multiple controls). /dev/media42 _is_ separate, but the entity that represents a PCM device is handled by the PCM code, so it would be possible to have a shortcut to get a PCM device's TLVs directly.
My concern is that accessing to different device files via yet another API in alsa-lib would be unnecessary overhead. (Since such information is demanded to be accessed through the normal ALSA API, we need a support in alsa-lib, anyway.
More question is whether this information should be available before or after hw_params setup.
This is pretty much static information, which is available even when the PCM device isn't opened.
If it's a static information that can be represented in TLV, we can provide it via the existing control API?
Meanwhile, the channel-mapping isn't always static. As Mark suggested, the channel mapping can be changed dynamically later. Some HD-audio codec allows it, and HD-audio controller allows the arbitrary stereo-wise mapping, too.
So, how flexible should it be -- it's a big question. If it's completely free-mappable, a style like TLV doesn't fit at all. In that case, we may need some mechanism like hw_constraint, too. OTOH, If it's something to select, providing a list of available modes would be feasible.
BTW, the channel-mapping info can be useful for the automatic plug layer, too.
And if there is a need for channel mapping information of ALSA plugins, there needs to be a userspace library for the media controller API.
I believe we need the alsa-lib, especially plugin access.
thanks,
Takashi
On Wed, Feb 08, 2012 at 10:23:45AM +0100, Takashi Iwai wrote:
Clemens Ladisch wrote:
Takashi Iwai wrote:
TLVs on media controller entities.
Well, my concern is that it might be too far from the other PCM stuff. How the implementation would look like?
It would be really good if it could support dynamic remapping of channels - for example, with most of the devices I work on you just get a bunch of audio channels presented to the mixing core of the device and can send them wherever it amuses you to do so at runtime, there's no fixed assignments.
participants (4)
-
Clemens Ladisch -
Mark Brown -
Patrick Lai -
Takashi Iwai