[uClinux-dev] Freescale's MCDMAAPI vs. Generic Linux DMA API on Coldfire MCF548x

[John Williams]

Hi,

Greg Ungerer wrote:

> Allon Stern wrote:
> 
>> On Feb 4, 2008, at 7:36 PM, Greg Ungerer wrote:
>>
>>> The current ColdFire DMA support in Linux is limited and a little
>>> out of date though, so it alone is not a good guide :-)
>>
>>
>> Any comments on the limitations?
> 
> Its just hasn't been looked at much over the years.
> It can certainly be brought up to date with the current
> kernel DMA API. Not sure how good a state the current
> code is in.
> 
> 
>> I'm hoping to use DMA in a device driver I'm writing for a 5282-based 
>> system.
> 
> 
> Using won't be a problem. Juts may take a little coding
> effort to bring it up to current standards.

I've been looking at the 2.6 kernel's generic DMA layer recently.  There 
are two aspects, the stuff described in DMA-IPA.txt is really more about 
how to allocate DMA-suitable memory regions for DMA, rather than the 
mechanics of DMA transactions themselves.

In the 2.6 kernel, drivers/dma/dmaengine.c implements a fairly generic 
DMA API for "standalone" DMA controllers, as opposed to DMA-capable 
peripherals (bus masters).  DMA controllers register themselves as 
devices, and clients register themselves as, well, clients.  THey then 
request a channel, and launch DMA transactiosn via the client API.

There are a few limitations that come its originals as an API for Intel 
DMA controllers (no striding or keyhole DMA support for example), but 
wouldn't be hard to extend.

Regards,

John