[alsa-devel] [RFC] AXD Audio Processing IP ALSA support - Questions

[Vinod Koul]

On Tue, Nov 04, 2014 at 09:48:18AM +0000, Qais Yousef wrote:
> Hi,
> 
> I have several questions on the best way to add AXD support in ALSA.
1st rule pls CC maintainers, so that it gets rights attention.

> The discussion of the previous patch can be found here:
> 
> https://lkml.org/lkml/2014/10/28/465
> 
> Questions:
> 
> 1- What is the best example to follow to add a simple mp3 support
> for AXD? The only one I find is in sst-mfld-platform-compress.c in
> sound/soc/intel directory but it's a bit confusing. I think because
> it's sharing code with several other sst drivers/platforms.
There are two ways
1. If you are a ASoC driver which is most likely the case, then add a
compress dai and then a compress dai-link. The device with compress device
will be created.
2. Directly call compress_register the way asoc does

For both you need to implement the compressed ops

> I find the documentation for compress_offload generally lacking. Is
> there a plan to improve on that? Being a new comer to ALSA framework
> api, I'm confused what is the correct way to do things :-/
Are you talking about kernel API or driver API? Can you please elaborate
> 
> So far I know I need to call snd_soc_register_card(). I thought
> snd_compress_register() (from compress_driver.h) is how you add
> compressed nodes to the card but apparently not. It looks like I
> need to define a compress_dai? Hmmm.
You need to define a compress_dai if you are a asoc device just like the pcm
dai's, it is similar to what you would need to do for PCM

> 2- Is tinycompress the only userland support for compress_offload?
> Is there anyone working on gstreamer and omx plugins to support
> that?
Yes, I don't know of anyone working on omx support.
> 
> Would tinycompress be part of alsa-utils and alsa-libs in the
> future? I know it needs more work at the moment but it'd be nice if
> compress_offload support is part of the standard alsa-utils and
> alsa-libs.
It is alsa-lib, for packaging we can make it part of alsa packages. Most
users are right now in Android so no one asked yet

> 3- Can we get an example of how transcoding (back to disk) is
> supposed to be working?
As I have replied to you last week, it would be done using two FEs and these
FEs should be "routed"
> 
> 4- How can we reconfigure complex audio effect components (like
> shelving filters) which need filter co-effecient changes to be
> applied all at once atomically to avoid instability?
Add an ALSA control which models sync, then in driver apply once you
get sync control

-- 
~Vinod

> My plan is to add mp3 driver first then build on that to add the
> rest of the features. Hopefully I can minimise the amount of work
> that needs doing (due to me doing it wrongly) and get features
> upstream sooner.
> 
> Thanks,
> Qais

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