[alsa-devel] [RFC PATCH 3/5] pxa: clean up the legacy SSP API

[Russell King - ARM Linux]

On Wed, Apr 29, 2009 at 05:14:13PM +0800, Eric Miao wrote:
> On Wed, Apr 29, 2009 at 4:41 PM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > On Wed, Apr 29, 2009 at 09:21:53AM +0100, Mark Brown wrote:
> >> On Wed, Apr 29, 2009 at 08:27:06AM +0100, Russell King - ARM Linux wrote:
> >> > On Tue, Apr 28, 2009 at 08:06:08PM -0300, Daniel Ribeiro wrote:
> >>
> >> > > The SPI subsystem?
> >>
> >> > Can the SPI system cope with the other chip being the master of the
> >> > interface.  In other words, can SPI sit around primed for a transfer,
> >> > and notify the user of SPI that new data has arrived?
> >>
> >> > If not, the SPI subsystem is totally unsuitable for this.
> >>
> >> It's slave only at the minute - there's holes in the API someone could
> >> fill in but that's not happened yet.
> >
> > Well, I guess someone else will have to do that; I don't spend much time
> > on the LX stuff, and so if it requires any time consuming work, it won't
> > be worth trying to get it into mainline.
> >
> 
> However, the patch itself doesn't looks like to be a SPI slave
> (I mean from the view of the processor).
> 
> 'struct spi_message' does support simultaneous rx/tx transfer
> and multiple such transfers being queued.

The transfers happen under control of PCON not the PXA; PCON asserts a
GPIO to activate the DMA to control when the transfer happens.

We can not just start the SSP for a 32 byte transfer and hope it happens.
PCON has to be totally in control.