Re: [PATCH v6 03/10] ARM: edma: add AM33XX support to the private EDMA API

[Matt Porter <mporter@ti.com>]

On Thu, Jan 31, 2013 at 08:58:39PM +0000, Arnd Bergmann wrote:
> On Thursday 31 January 2013, Matt Porter wrote:
> > On Wed, Jan 30, 2013 at 09:32:58AM +0000, Arnd Bergmann wrote:
> > > On Wednesday 30 January 2013, Matt Porter wrote:
> > > > +               dma_cap_set(DMA_SLAVE, edma_filter_info.dma_cap);
> > > > +               of_dma_controller_register(dev->of_node,
> > > > +                                          of_dma_simple_xlate,
> > > > +                                          &edma_filter_info);
> > > > +       }
> > > 
> > > How do you actually deal with the problem mentioned by Padma, that
> > > the filter function does not know which edma instance it is looking
> > > at? If you assume that there can only be a single edma instance in
> > > the system, that is probably a limitation that should be documented
> > > somewhere, and ideally the probe() function should check for that.
> > 
> > I make an assumption of one edma instance in the system in the case of
> > DT being populated. This is always true right now as the only SoC with
> > two EDMA controllers in existence is Davinci DA850. Until recently,
> > Davinci had no DT support. Given the steady work being done today on DT
> > support for DA850, it'll probably be something needed in 3.10.
> > 
> > I will add a comment and check in probe() to capture this assumption
> > and then plan to update separately to support DA850 booting from DT.
> 
> Ok, sounds good. Hopefully by then we will already have a nicer
> way to write an xlate function that does not rely on a filter
> function.

Yes, it would be nice to avoid what Padma had to do. I should have
mentioned also that the second EDMA on DA850 has no DMA events of
immediate use on it anyway. All the in-kernel users use events on the
first controller, except for the second MMC instance. That's only used
for a wl12xx module on the EVM and that driver has no DT support so it
doesn't matter yet in the DT case. Because of this, DA850 can actually
add EDMA DT support immediately (on top of this series) and add DMA
support to the DT support already posted for the Davinci SPI and MMC
client drivers.

-Matt