[alsa-devel] Separate dma driver for cpu_dais

[jassi brar]

On Thu, Feb 18, 2010 at 10:10 PM, Mark Brown
<broonie at opensource.wolfsonmicro.com> wrote:
> On Thu, Feb 18, 2010 at 08:59:38PM +0900, jassi brar wrote:
>> On Thu, Feb 18, 2010 at 7:57 PM, Mark Brown
>> IMO codecs should simply do as directed by the ASOC.
>
> Right, but that doesn't mean that the device drivers can't do anything
> useful here - in terms of restrictions they can't do anything the
> hardware can't implmenent.  Another example here is that startup
> function can set constraints based on the configuration of other running
> links if the hardware has any limitations in that regard (some will,
> some won't, and the limitations may not even be anything to do with
> audio in some designs).
Okay. Here's another perspective ...
If a dai can have further parallel sub-configurations, perhaps it should
be further divided into more dais.
So, I see a snd_soc_dai as the simplest h/w unit in the system and
presumably  already fully exploited by the active dai_link i.e, none of
its bits can be changed without disturbing the active stream. The
number of shares should be transparent to a dai.
If this assumption is valid please read on, otherwise correct me.

The set of {rate, sample size & format, channels} defines one active
dai. The second stream sharing this dai can not change any of these
parameters without spoiling the active playback/capture - we can allow
this configuration overriding as a feature or prevent as a bug. I
prefer latter. Since there isn't anything new to do now, the ASoC core
can
simply avoid calling hooks in drivers rather than having 50 drivers
implement a check.