Re: [PATCH 5/5] arm: dts: Convert mvebu device tree files to 64bits
From: Thomas Petazzoni
Date: Thu Mar 21 2013 - 17:16:22 EST
Dear Andrew Lunn,
On Thu, 21 Mar 2013 21:37:51 +0100, Andrew Lunn wrote:
> > And I'm not sure the SDRAM address decoding windows allows to split the
> > first 4 GB of RAM into two areas, one that would be mapped starting at
> > physical address 0x0, and another area that would be mapped at a
> > different address (above 4 GB).
> So why not map the whole SDRAM above 4GB physical address?
As Lior rightly pointed out to me, this would prevent any device from
DMA-ing to or from the RAM. Devices can only access the first 32 bits
of the physical address space. So there must be some RAM below 4 GB.
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
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