[PATCH 01/10] ARM: change ARM_DMA_ZONE_SIZE into a variable
grant.likely at secretlab.ca
Thu Jul 7 14:15:26 EDT 2011
On Thu, Jul 07, 2011 at 06:17:11PM +0200, Arnd Bergmann wrote:
> On Thursday 07 July 2011, Nicolas Pitre wrote:
> > > What is hardware specific is that the DMA devices can only address a
> > > limited range of memory. IMHO it's that which should be described in
> > > DT, not that we'll have a DMA zone of X bytes in size.
> > I think that we all agree on the principle. I certainly never intended
> > to suggest that the DMA zone size be stored as is in the device tree.
> There is a way to specify DMA address ranges in the device tree, though
> I forgot the exact format. It comes down to saying the device sees
> memory range XXX to YYY as its local address AAA to BBB. We could use
> that information at boot time to determine what the largest range
> of memory is that is visible by all devices (and hope that it's at
> the start of physical memory).
It's called dma-ranges, and it has the same syntax as the ranges
property. See section 2.3.9 on page 30 in ePAPR:
This describes the hardware constraints, not the DMA zone size or
any software decisions like that.
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