[alsa-devel] [PATCH 1/4] ASoC: pxa-ssp: enhance I2S and add Left_J support

[Mark Brown]

On Mon, Jun 08, 2009 at 10:13:25PM +0800, Eric Miao wrote:
> On Mon, Jun 8, 2009 at 8:12 PM, pHilipp Zabel<philipp.zabel at gmail.com> wrote:

> > Agreed. Also, if I had to use this to configure magician with DSP_A
> > (right now it says I2S and LEFT_J only, but why limit it to that?),
> > I'd need an additional PXA_SSP_FRM_16FS.

> That shouldn't be a problem - it can just be added.

That won't scale in a bitmask - as you get more and more slots in use on
a TDM system more and more slots are going to need to extend the range
of values you can set in a bitmask.  Consider what happens when people
start hanging 5.1 CODECs off TDM buses with single data lines, for
example.

> >> sample width parameter to set_tdm_slot() - given the very small number
> >> of in tree users it'd cause little disruption.  A set_sample_width()
> >> operation could also be added.

> Well, the real problem is that it's quite difficult to abstract all
> the different formats into a single structure. I'd prefer to have
> something specific at the begining.

I don't see much difference between any of the proposals here (or any
problem with format-specificness) - my main thing here is to pull the
frame width configuration out of the DAI format.

> > set_sample_width or set_frame_width?
> > I'd prefer a separate operation over a parameter to set_tdm_slot because
> > in my setup I just need to force the (SSP) frame width to 16 bits.
> > Enabling network mode and calling set_tdm_slot(..,1,1) wouldn't be
> > necessary at all, then.

> As said, if we can invent something like a single structure
> making all formats happy, it will be good. However, before
> that's possible, I'd really prefer less API for the formats being
> further introduced, so we go no further from that goal.

Well, if we want to avoid introducing a new API at all then the PXA SSP
driver is going to need to figure out the bit clock rate automatically
from the TDM and sample size configuration - if it needs to be
explicitly specified then it's a new API and once we introduce one way
of doing this it'll probably stick.

TDM really needs some sort of frame/sample width configuration to work
well so I think we're better off adding a standard API now.