Re: [PATCH 2/2 V3] MXS: Implement DMA support into mxs-i2c

[Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

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On Sun, Jul 15, 2012 at 04:17:16PM +0800, Shawn Guo wrote:
> On Fri, Jul 13, 2012 at 10:22:49AM +0200, Wolfram Sang wrote:
> > > +	/*
> > > +	 * TODO: This is a temporary solution and should be changed
> > > +	 * to use generic DMA binding later when the helpers get in.
> > > +	 */
> > 
> > @Shawn: Any idea when this is going to happen? And why do we need this?
> 
> See thread [1] for current statues.  I'm not sure when it's going to
> happen though.

Phew, [1] is a bit too much too read. I will just assume there are still
issues.

> > AFAICT it will be always channel 6/7 on mx28?
> > 
> Yes, but it might be a different channel on mx23.  Just like we define
> IO region and interrupt number in device tree, dma channel is just
> another resource of hardware block that we choose to define in device
> tree.

What makes me wonder now that I come to think of it (not necessarily a
question for Shawn but to all):

If I have an I2C slave with an interrupt line tied to something, GPIO or
external IRQ from the SoC, it makes perfect sense to define that in the
devicetree.

Yet, if I know the compatible property for the mxs I2C driver, and also
know the CPU type (be it MX23 or MX28), I can deduce from that a lot of
information, including DMA channel. That is fix. Why encode it?

Regards,

   Wolfram

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