linux-kernel - Re: [RFC PATCH 0/3] Separate BE DAI HW constraints from FE ones

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Date:   Fri, 16 Apr 2021 11:47:01 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Mark Brown <broonie@...nel.org>, Codrin.Ciubotariu@...rochip.com
Cc:     alsa-devel@...a-project.org, lgirdwood@...il.com,
        linux-kernel@...r.kernel.org, tiwai@...e.com,
        gustavoars@...nel.org, mirq-linux@...e.qmqm.pl
Subject: Re: [RFC PATCH 0/3] Separate BE DAI HW constraints from FE ones

On 4/16/21 11:31 AM, Mark Brown wrote:
> On Fri, Apr 16, 2021 at 04:03:05PM +0000, Codrin.Ciubotariu@...rochip.com wrote:
> 
>> Thank you for the links! So basically the machine driver disappears and
>> all the components will be visible in user-space.
> 
> Not entirely - you still need something to say how they're wired
> together but it'll be a *lot* simpler for anything that currently used
> DPCM.
> 
>> If there is a list with the 'steps' or tasks to achieve this? I can try
>> to pitch in.
> 
> Not really written down that I can think of.  I think the next steps
> that I can think of right now are unfortunately bigger and harder ones,
> mainly working out a way to represent digital configuration as a graph
> that can be attached to/run in parallel with DAPM other people might
> have some better ideas though.  Sorry, I appreciate that this isn't
> super helpful :/

I see a need for this in our future SoundWire/SDCA work. So far I was 
planning to model the entities as 'widgets' and lets DAPM propagate 
activation information for power management, however there are also bits 
of information in 'Clusters' (number of channels and spatial 
relationships) that could change dynamically and would be interesting to 
propagate across entities, so that when we get a stream of data on the 
bus we know what it is.

when we discussed the multi-configuration support for BT offload, it 
also became apparent that we don't fully control the sample rate changes 
between FE and BE, we only control the start and ends. I fully agree 
that the division between front- and back-ends is becoming limiting and 
DPCM is not only complicated but difficult to stretch further.