[RFC/RFT 2/2] ARM: keystone: Install hooks for dma address translation routines

Olof Johansson olof at lixom.net
Tue Feb 4 11:22:32 EST 2014

On Tue, Feb 4, 2014 at 8:01 AM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Tuesday 04 February 2014, Santosh Shilimkar wrote:
>> > PPC servers use "ibm,dma-window" to describe the assigned dma address
>> > space for busses/devices, but the window itself doesn't contain any
>> > information about the physical address mapping (since it goes through
>> > an iommu after that). It likely doesn't fit this particular use case,
>> > but it's something we should look at as a base in case we need to
>> > start looking at bindings for this instead of coding it per SoC. We'll
>> > know more once we've seen what a few of the implementations out there
>> > are.
>> >
>> Understood.
> I think you are looking for the "dma-ranges" property, which describes
> how a device DMA address space maps into the parent bus address space
> for inbound translations. It's not used much in Linux, but it is clearly
> specified. The "ibm,dma-window" property OTOH is for the corner case
> that you have a small per-partition DMA address space section, which is
> not how things are done on most systems these days.

Ah, that might very well be the case. And it looks like dma-ranges
handles this case already. At least based on the first draft proposal
for dma-ranges that I came across. :)


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