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

[Greg Ungerer]

Hi Markus,

Markus Franke wrote:
> thanks for the reply.
> 
> Zitat von John Williams <jwilliams at itee.uq.edu.au>:
> 
>> 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.
> 
> That's exactly what I was thinking.
> 
>> 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.
> 
> I am quite surprised to see this API. Thanks for the hint. Actually I 
> was thinking about to provide functions like request_dma, free_dma, 
> set_dma_count, set_dma_address, etc. in arch/m68knommu/dma.c for my 
> MCF548x.
> 
> So what is the prefered way now or are both ways equal and it's just a 
> matter of taste?

Hmm, good question. There doesn't seem to be much architecture
support for the generic code in drivers/dma/. Really there are
not a lot of users of the traditional *_dma() interface either.

Plenty of other architectures still seem to have a asm-*/dma.h,
with real support. So that API still seems to be alive.

Regards
Greg


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