[PATCH v5 1/3] ARM: add CPPI 4.1 DMA support

Felipe Balbi balbi at ti.com
Mon Jan 3 15:49:52 EST 2011


On Mon, Jan 03, 2011 at 05:19:45PM +0000, Russell King - ARM Linux wrote:
>>    Frankly speaking, I doubt that drivers/dma/ will have place for the
>> purely MUSB specific DMA engines such as the named ones (there's no TUSB
>> DMA BTW -- it uses OMAP DMA).
>Long term, we need to kill off all these platform private DMA interfaces.
>There's a growing amount of IP that's being shared not only between ARM
>silicon vendors, but also across architectures, and having to re-implement
>drivers because the underlying DMA engine is different is not feasible.
>For example, we're seeing ARMs primecells being used with various
>different DMA controllers in various different ARM SoCs.  I've heard
>rumours of them appearing in MIPS or PPC stuff as well.  We're seeing
>PXA peripheral IP appearing in x86 stuff too.
>We can't have drivers tied to their SoC DMA engines, and we can't continue
>having SoC DMA engines implementing their own unique APIs.  We do need to
>get on top of this before it becomes a major problem (if it hasn't
>The DMA engine API is still evolving, and should not be taken as concrete
>- I've recently been bringing up a number of points with Dan on various
>aspects of the API, some of which ultimately will lead to changes to the
>async-tx API, and others which hopefully will mean that the DMA slave
>API is better documented.

I couldn't agree more with you Russell. If the API isn't enough
currently, we can always propose an extension.

Having all sorts of SoC-specific "APIs" has already caused enough
problems and it still does (non-generic IRQ handling on
twl?030, menelaus, cbus - which isn't in mainline yet -, etc,
non-generic McBSP usage, non-generic GPMC usage, etc etc). So, if we can
plan for making use of generic APIs, let's do so.


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