Re: [PATCH 00/13] pxa3xx patches to support mvebu builds

[Ezequiel Garcia <ezequiel.garcia@free-electrons.com>]

On Tue, Jul 30, 2013 at 03:22:25PM +0200, Daniel Mack wrote:
[...]
> > Mmmm.. I'm a bit confused by this: is your dmaengine driver any
> > different/better from the already existent mmp_{p,t}dma.c ?
> 
> As I said, I saw this after I started my own implementation, which isn't
> a big deal. At least, I now understand the internals of dmaengine
> drivers :) The mmp_pdma looks suitable for PXA2xx chips, but it doesn't
> work yet for me. I'll try and fix this first, and then port over all the
> drivers.
> 
> > Here's a patch posted in July 2012 converting pxa3xx-nand to dmaengine.
> 
> Where?
> 

Ouch... here it is:

http://permalink.gmane.org/gmane.linux.ports.arm.kernel/178989

(sorry about that...)

That patch was part of this series:

http://comments.gmane.org/gmane.linux.ports.arm.kernel/181731

But as you can see in the above link, they dropped the pxa3xx-nand part.

> > That patch was never merged because (just as Thomas says) both
> > dma drivers (mmp dmaengine on one side, mach-pxa dma on the other) don't
> > work together. In other words, you have to convert *all* drivers at the
> > same time.
> > 
> > Thomas proposed an idea for this conversion a few months ago: (quoting
> > him from IRC)
> > 
> > """
> > First have a patch that reimplements the existing plat-pxa/dma.c API on
> > top of dmaengine, so that you don't have to change any driver.
> > Then, go through each driver, one per patch to switch to the dmaengine API.
> > And finally get rid of the compatibility layer created in the first
> > patch.
> > """
> > 
> > Does this sound sane?
> 
> Unfortunately, no. I thought so too, but the problem is that all users
> of the proprietary PXA DMA implementation access the registers directly,
> and also allocate their own DMA coherent register space, which is
> unneeded with a proper dmaengine implementation.
> 
> So there's nothing else we can do than really change all the drivers,
> which is what I'm currently doing.

Oh, I see. 

> I'll put you on Cc: once I post patches.
> 

Great! That'll be very appreciated.

-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com