Re: DT DMA channel binding for Tegra I2S

[Mark Brown <broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>]

On Sat, Nov 26, 2011 at 10:07:01PM -0600, Rob Herring wrote:
> On 11/25/2011 10:09 AM, Mark Brown wrote:
> > On Fri, Nov 25, 2011 at 09:55:23AM -0600, Rob Herring wrote:

> >> Although, I think you are possibly missing some other properties for
> >> i2s mode like word size and master/slave mode. I think the ideal case
> >> is that a single ASoC platform driver for DT could handle multiple
> >> SoCs.

> > No.  You're not going to be able to get a single binding which handles
> > the setup for all systems based off a given SoC let alone multiple SoCs.
> > It is possible to come up with some subsets which work over multiple
> > boards but that's going to be outside the binding for the I2S controller
> > and in a board audio hardware binding for the subset.

> I never said a single binding. Part of device tree is describing how
> devices are connected together which is a large part of the audio
> configuration. Whether there's one common driver or not doesn't really
> matter. The important part right now is to define the bindings and do so
> in a common way where possible.

That's what I'm hearing when I hear you talk about things like defining
a binding that works for multiple SoCs or which defines stuff like word
size and master/slave mode (word size especially needs to be a runtime
property).

> My original point really was that when defining a binding, it should be
> as complete as possible rather than done incrementally over time. You
> are describing the h/w, and that's not changing. For an i2s block, only
> having a dma channel is definitely not complete.

The binding posted had DMA, registers and IRQ which seems like exactly
what I'd expect for an I2S controller - the reason only DMA was being
highlighted is that that's the only bit with a lack of clarity on the
bindings.

> > This has been discussed repeatedly, we really need to work out how to
> > educate device tree people about this stuff, it gets *very* repetitive
> > having the discussion over and over again.

> As you might guess, audio is not an area I have been spending time on
> recently. Perhaps seeing a complete binding with all the pieces (codec,
> i2s, misc gpio's, etc.) would help educate us.

Stephen's patches are the closest I've seen yet to what's been decided.

This is exactly the sort of concern I have with education - we've been
through this discussion repeatedly and yet every time a new person from
the OF side turns up we have to go through the same explanations and
discussion again.  Like I say this really does get very repetitive.