[RFC] AXD Audio Processing IP ALSA support - Questions

[RFC] AXD Audio Processing IP ALSA support - Questions

[Qais Yousef]

Hi,

I have several questions on the best way to add AXD support in ALSA.

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.

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 :-/

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.

2- Is tinycompress the only userland support for compress_offload? Is 
there anyone working on gstreamer and omx plugins to support that?

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.

3- Can we get an example of how transcoding (back to disk) is supposed 
to be working?

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?

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

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Clemens Ladisch]

Qais Yousef wrote:
> 3- Can we get an example of how transcoding (back to disk) is supposed to be working?

ALSA PCM devices are assumed to run with their own clock, i.e., it is
not directly possible for applications to control when a playback device
reads data from the ring buffer, of when a capture device writes data to
it.  The ALSA API is designed for real-time opertation; it would not be
a good choice for batch conversions.


Regards,
Clemens

Re: [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

-- 

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Vinod Koul]

On Tue, Nov 04, 2014 at 10:58:52AM +0100, Clemens Ladisch wrote:
> Qais Yousef wrote:
> > 3- Can we get an example of how transcoding (back to disk) is supposed to be working?
> 
> ALSA PCM devices are assumed to run with their own clock, i.e., it is
> not directly possible for applications to control when a playback device
> reads data from the ring buffer, of when a capture device writes data to
> it.  The ALSA API is designed for real-time opertation; it would not be
> a good choice for batch conversions.
ALSA Compressed devices can be used here

-- 
~Vinod

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Qais Yousef]

On 11/04/2014 10:40 AM, Vinod Koul wrote:
> 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.
>

OK sorry about that.

>> 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

Thanks for the pointers :)

>> 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

Driver API. A new section in 'Writing an ALSA Driver' for compress 
offload would be helpful for example.

snd_compress_register() for example is not clear in what context it 
needs to be called. I failed to find any reference to a user. In your 
pointers above I was trying to do 1 and 2 simultaneously - I didn't 
realise that 1 makes 2 unnecessary.

It might be that I just need to spend more time on it to get it.

>> 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

I'm using buildroot for my testing. So if it's included part of alsa 
packages that would be helpful.
Also it'll help with getting gstreamer support.

>> 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"

OK. I need to read more to completely understand this to be honest. I 
don't know what's an FE and I don't know how they can be 'routed'. 
That's why I was hoping to get an example or a pointer to anything that 
does a similar thing.
Just to clarify, all the necessary bits are there and I just need to use 
them?

>> 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
>

OK. It's good to know the support for this type of operations is already 
available.

Thanks,
Qais

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Pierre-Louis Bossart]

On 11/4/14, 6:04 AM, Qais Yousef wrote:
> On 11/04/2014 10:40 AM, Vinod Koul wrote:
>> 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.
>>
>
> OK sorry about that.
>
>>> 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
>
> Thanks for the pointers :)
>
>>> 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
>
> Driver API. A new section in 'Writing an ALSA Driver' for compress
> offload would be helpful for example.
>
> snd_compress_register() for example is not clear in what context it
> needs to be called. I failed to find any reference to a user. In your
> pointers above I was trying to do 1 and 2 simultaneously - I didn't
> realise that 1 makes 2 unnecessary.
>
> It might be that I just need to spend more time on it to get it.
>
>>> 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
>
> I'm using buildroot for my testing. So if it's included part of alsa
> packages that would be helpful.

tinycompress (just like tinyalsa) have a different license and different 
maintainers.

> Also it'll help with getting gstreamer support.

in a gstreamer/pulseaudio setting, the plan was to pass all the data 
through pulseaudio using IEC packets (to allow for byte-ms conversions) 
and have a sink that would perform the needed conversion using 
tinycompress (totally hardware specific). Direct access from gstreamer 
to tinycompress gets in the way of audio routing/volume control handled 
in pulseaudio. I think this was presented at Plumbers 3-4 years ago.
But as Vinod said, we've only heard of Android usages so far.

>
>>> 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"
>
> OK. I need to read more to completely understand this to be honest. I
> don't know what's an FE and I don't know how they can be 'routed'.
> That's why I was hoping to get an example or a pointer to anything that
> does a similar thing.
> Just to clarify, all the necessary bits are there and I just need to use
> them?

Front-ends are typically 'logical' streams visible to the host.
Back-ends are typically physical links.
FEs and BEs are usually linked through a mixing/routing structure where 
ALS controls define what gets played where and where you record from.
As Vinod mentioned, you can define a mixing/routing structure where the 
decoded data is fed back to an encoder for record applications. Note 
that if your goal is to transcode faster than real-time you will need a 
dedicated routing structure that isn't linked to any BE timing - 
otherwise the transcoding will be throttled by link timings.

>>> 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
>>
>
> OK. It's good to know the support for this type of operations is already
> available.

Such effects typically rely on a 'commit' operation to apply all 
parameters at once (avalaible in OpenSL ES). You'd need to link your 
user-space commit operation with low-level procedure that lets your DSP 
apply everything in one shot. The infrastructure exists but how you 
implement the commit part is not generic at all. It could be a dedicated 
alsa control or a bitfield in a 512-byte binary control - your choice 
really.

>
> Thanks,
> Qais
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Mark Brown]

[-- Attachment #1.1: Type: text/plain, Size: 902 bytes --]

On Tue, Nov 04, 2014 at 10:14:32AM -0600, Pierre-Louis Bossart wrote:
> On 11/4/14, 6:04 AM, Qais Yousef wrote:

> >OK. I need to read more to completely understand this to be honest. I
> >don't know what's an FE and I don't know how they can be 'routed'.
> >That's why I was hoping to get an example or a pointer to anything that
> >does a similar thing.
> >Just to clarify, all the necessary bits are there and I just need to use
> >them?

> Front-ends are typically 'logical' streams visible to the host.
> Back-ends are typically physical links.

Well, they're both physical usually - generally the front end is the DMA
stream that userspace interacts with while a back end is an electrical
interface on the edge of the SoC.  Either can potentially be virtual,
though most implementations do have something physical behind them (a
DMA controller for the FE, a physical audio interface for the BE).

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Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Qais Yousef]

On 11/04/2014 04:14 PM, Pierre-Louis Bossart wrote:
> On 11/4/14, 6:04 AM, Qais Yousef wrote:
>> On 11/04/2014 10:40 AM, Vinod Koul wrote:
>>> 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.
>>>
>>
>> OK sorry about that.
>>
>>>> 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
>>
>> Thanks for the pointers :)
>>
>>>> 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
>>
>> Driver API. A new section in 'Writing an ALSA Driver' for compress
>> offload would be helpful for example.
>>
>> snd_compress_register() for example is not clear in what context it
>> needs to be called. I failed to find any reference to a user. In your
>> pointers above I was trying to do 1 and 2 simultaneously - I didn't
>> realise that 1 makes 2 unnecessary.
>>
>> It might be that I just need to spend more time on it to get it.
>>
>>>> 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
>>
>> I'm using buildroot for my testing. So if it's included part of alsa
>> packages that would be helpful.
>
> tinycompress (just like tinyalsa) have a different license and 
> different maintainers.
>
>> Also it'll help with getting gstreamer support.
>
> in a gstreamer/pulseaudio setting, the plan was to pass all the data 
> through pulseaudio using IEC packets (to allow for byte-ms 
> conversions) and have a sink that would perform the needed conversion 
> using tinycompress (totally hardware specific). Direct access from 
> gstreamer to tinycompress gets in the way of audio routing/volume 
> control handled in pulseaudio. I think this was presented at Plumbers 
> 3-4 years ago.

Useful. Hopefully I can find online references to this discussion.

> But as Vinod said, we've only heard of Android usages so far.
>
>>
>>>> 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"
>>
>> OK. I need to read more to completely understand this to be honest. I
>> don't know what's an FE and I don't know how they can be 'routed'.
>> That's why I was hoping to get an example or a pointer to anything that
>> does a similar thing.
>> Just to clarify, all the necessary bits are there and I just need to use
>> them?
>
> Front-ends are typically 'logical' streams visible to the host.
> Back-ends are typically physical links.
> FEs and BEs are usually linked through a mixing/routing structure 
> where ALS controls define what gets played where and where you record 
> from.
> As Vinod mentioned, you can define a mixing/routing structure where 
> the decoded data is fed back to an encoder for record applications. 
> Note that if your goal is to transcode faster than real-time you will 
> need a dedicated routing structure that isn't linked to any BE timing 
> - otherwise the transcoding will be throttled by link timings.
>
>>>> 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
>>>
>>
>> OK. It's good to know the support for this type of operations is already
>> available.
>
> Such effects typically rely on a 'commit' operation to apply all 
> parameters at once (avalaible in OpenSL ES). You'd need to link your 
> user-space commit operation with low-level procedure that lets your 
> DSP apply everything in one shot. The infrastructure exists but how 
> you implement the commit part is not generic at all. It could be a 
> dedicated alsa control or a bitfield in a 512-byte binary control - 
> your choice really.
>

Many thanks for all the clarifications. I think I better understand how 
it should work now and what to search/look for.

Cheers,
Qais

>>
>> Thanks,
>> Qais
>> _______________________________________________
>> Alsa-devel mailing list
>> Alsa-devel@alsa-project.org
>> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Vinod Koul]

On Tue, Nov 04, 2014 at 12:04:26PM +0000, Qais Yousef wrote:
> On 11/04/2014 10:40 AM, Vinod Koul wrote:
> >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.
> >
> 
> OK sorry about that.
> 
> >>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
> 
> Thanks for the pointers :)
> 
> >>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
> 
> Driver API. A new section in 'Writing an ALSA Driver' for compress
> offload would be helpful for example.
Not really. I think Writing ASoC driver would help :)

More I think of you issues, it seems to me that first you need to comprehend
how ASoC works and model your device properly. The things like registers
which were in last post would be modeled as ASoC widgets. Once you
comprehend that then the compress is just a dai, dailink and ops addition.

> 
> snd_compress_register() for example is not clear in what context it
> needs to be called. I failed to find any reference to a user. In
> your pointers above I was trying to do 1 and 2 simultaneously - I
> didn't realise that 1 makes 2 unnecessary.
If you are asoc driver then you do need to worry about it as based on
dailinks, core will call this.

> 
> It might be that I just need to spend more time on it to get it.
> 
> >>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
> 
> I'm using buildroot for my testing. So if it's included part of alsa
> packages that would be helpful.
> Also it'll help with getting gstreamer support.
> 
> >>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"
> 
> OK. I need to read more to completely understand this to be honest.
> I don't know what's an FE and I don't know how they can be 'routed'.
> That's why I was hoping to get an example or a pointer to anything
> that does a similar thing.
> Just to clarify, all the necessary bits are there and I just need to
> use them?
Mostly yes, but if you have a typical example which doesnt work, we should
be able to add support for that in framework.
I think transcoding (FE-FE) should work like we have BE-BE loopback
working today. Noone has built it for this usage and tested it. So I would
expect some fixes to framework too.

-- 
~Vinod
> 
> >>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
> >
> 
> OK. It's good to know the support for this type of operations is
> already available.
> 
> Thanks,
> Qais

-- 

Re: [RFC] AXD Audio Processing IP ALSA support - Questions

[Qais Yousef]

On 11/05/2014 08:38 AM, Vinod Koul wrote:
> On Tue, Nov 04, 2014 at 12:04:26PM +0000, Qais Yousef wrote:
>> On 11/04/2014 10:40 AM, Vinod Koul wrote:
>>> 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.
>>>
>> OK sorry about that.
>>
>>>> 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
>> Thanks for the pointers :)
>>
>>>> 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
>> Driver API. A new section in 'Writing an ALSA Driver' for compress
>> offload would be helpful for example.
> Not really. I think Writing ASoC driver would help :)
> More I think of you issues, it seems to me that first you need to comprehend
> how ASoC works and model your device properly. The things like registers
> which were in last post would be modeled as ASoC widgets. Once you
> comprehend that then the compress is just a dai, dailink and ops addition.
>

I'm reading and writing more code and getting better grasp of the terms 
and structures/model :)

>> snd_compress_register() for example is not clear in what context it
>> needs to be called. I failed to find any reference to a user. In
>> your pointers above I was trying to do 1 and 2 simultaneously - I
>> didn't realise that 1 makes 2 unnecessary.
> If you are asoc driver then you do need to worry about it as based on
> dailinks, core will call this.
>
>> It might be that I just need to spend more time on it to get it.
>>
>>>> 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
>> I'm using buildroot for my testing. So if it's included part of alsa
>> packages that would be helpful.
>> Also it'll help with getting gstreamer support.
>>
>>>> 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"
>> OK. I need to read more to completely understand this to be honest.
>> I don't know what's an FE and I don't know how they can be 'routed'.
>> That's why I was hoping to get an example or a pointer to anything
>> that does a similar thing.
>> Just to clarify, all the necessary bits are there and I just need to
>> use them?
> Mostly yes, but if you have a typical example which doesnt work, we should
> be able to add support for that in framework.
> I think transcoding (FE-FE) should work like we have BE-BE loopback
> working today. Noone has built it for this usage and tested it. So I would
> expect some fixes to framework too.
>

OK understood. If it's only bug fixes then that's comparatively easier :)

Many thanks,
Qais