linux-kernel - Re: [PATCH 00/11] Add AXD Audio Processing IP driver

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Date:	Tue, 28 Oct 2014 15:33:55 +0000
From:	Qais Yousef <qais.yousef@...tec.com>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Clemens Ladisch <clemens@...isch.de>,
	<linux-kernel@...r.kernel.org>
CC:	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<devicetree@...r.kernel.org>, <alsa-devel@...a-project.org>,
	Neil Jones <neil.jones@...tec.com>
Subject: Re: [PATCH 00/11] Add AXD Audio Processing IP driver

On 10/28/2014 02:54 PM, Lars-Peter Clausen wrote:
> On 10/28/2014 02:18 PM, Qais Yousef wrote:
>> On 10/28/2014 11:55 AM, Clemens Ladisch wrote:
>>> Qais Yousef wrote:
>>>> AXD Audio Processing IP performs audio decoding, encoding, mixing,
>>>> equalisation,
>>>> synchronisation and playback.
>>> What exactly do you mean with "synchronisation" and "playback"?
>>
>> Synchronisation refers to accurate audio playout relative to a master
>> clock source including compensation of drift between the master clock
>> source and the playout clock of the audio hardware. Hence allowing
>> synchronised audio playout across multiple independent devices.
>>
>> Playback simple refers to the fact that AXD is capable of managing audio
>> playout hardware like I2S and SPDIF interfaces.
>>
>>
>>>> It doesn't fit in alsa subsystem but I Cced them to confirm.
>>> ... because those two words sound like something that a sound card 
>>> could do.
>>
>> The problem mainly stems from the fact that we take a variety of
>> compressed audio as input and we could perform audio encoding. The
>> problem with the compressed audio is that the range of decoders and
>> configuration supported in alsa is limited and there's no support for
>> taking raw pcm and producing compressed output. I'm not an expert on
>> alsa but when I looked it looked like there's more infra structure
>> required.
>>
>> [...]
>
> This doesn't sound to different from any of the other supported audio 
> DSPs. ALSA seems to have 95% of what you need. And the missing 5% is 
> probably stuff that is not specific to your hardware but rather 
> something that other hardware will need as well. The framework is not 
> set in stone you can make modifications and add the features that are 
> missing to make your hardware work.
>
> E.g. look at sound/soc/intel/ for an example of a audio DSP.
>
> No integrating this into ALSA will quite likely result in a quite 
> messy situation for you on the long run.
>
> - Lars
>
>
>
OK thanks for the reference. To be honest it felt like 15-20% of the 
features are missing but I'll need to look at the specifics and 
judge/estimate better.

Thanks,
Qais
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