Re: [RESEND RFC PATCH 1/3] ASoC: mediatek: Add binding support for AFE driver

[Koro Chen <koro.chen@mediatek.com>]

On Tue, 2015-04-21 at 11:49 +0200, Sascha Hauer wrote:
> On Mon, Apr 20, 2015 at 09:48:49PM +0100, Mark Brown wrote:
> > On Mon, Apr 20, 2015 at 06:37:47AM +0200, Sascha Hauer wrote:
> > > On Sat, Apr 18, 2015 at 06:34:07PM +0100, Mark Brown wrote:
> > > > On Fri, Apr 10, 2015 at 04:14:07PM +0800, Koro Chen wrote:
> > 
> > > > > +Each external interface (called "IO" in this driver) is presented as a
> > > > > +DAI to ASoC. An IO must be connected via the interconnect to a memif.
> > > > > +The connection paths are configured through the device tree.
> > 
> > > > Why are these connection paths configured via device tree?  I would
> > > > expect that either there would be runtime configurability of these
> > > > things (particularly if loopback configurations within the hardware are
> > > > possible) or we'd just allocate memory interfaces to DAIs automatically
> > > > as DAIs come into use.
> > 
> > > There is a crossbar switch between the memory interfaces and the DAIs.
> > > Not every connection is possible, so not every memory interface can be
> > > used for every DAI. An algorithm choosing a suitable memory interface
> > > must be quite clever, complicated and also SoC dependent (the same but
> > > different hardware is used on MT8135 aswell), so I thought offering a
> > > static configuration via device tree is a good start. Should there be
> > > runtime configuration possible later the device tree settings could
> > > provide a good default.
> > 
> > What exactly do the restrictions look like and how often do they vary in
> > practice (can we get away with just doing a single static setup in the
> > driver)? I'd have thought it should be fairly straightforward to have a
> > table of valid mappings and just pick the first free memory interface?
> 
> I think this could be done. I checked the possible connections in the
> crossbar switch and it seems all memory interfaces can be connected with
> all relevant external interfaces. So indeed the memory interfaces could
> be dynamically allocated instead of statically associated to an
> external interface. There are two problems I see: Some memory interfaces
> are limited in the rates they support, they can only do 8k/16k/32k (for
> speech). How can we know such memory interface should be used? Also
The 2 memif are "DAI" and "MOD_DAI", designed for speech cases, and they
should be only connected to corresponding external interface "DAI/BT"
and "modem", respectively. We don't need to put them into dynamic
allocation. 
> there are two programmable hardware gain blocks which can be inserted to
> the digital audio path using the crossbar switch. There must be some
> mechanism to configure them into different places.
Maybe in DPCM, they can be "widgets", and we can define "routes" and
corresponding controls for them. 
> 
> Sascha
>