Subject: [PATCH v3 11/12] ARM: mvebu: Relocate Armada 370 PCIe device tree nodes

From: [email-masked] (Arnd Bergmann)
Date: Wed, 19 Jun 2013 20:55:41 +0200

On Wednesday 19 June 2013, Jason Gunthorpe wrote:
> 
> Today 18:53:48
>    
> On Wed, Jun 19, 2013 at 02:11:58PM +0200, Arnd Bergmann wrote:
> 
> > > Mmm.. and why is this option acceptable?
> > 
> > As I explained on IRC, there is no requirement to pick a specific bus
> > aperture. The only two sensible choices are to make the bus address
> > the same as the CPU address, or to make the bus address start at 0,
> > which is what this does.
> 
> PCI bus addresses must not alias other addresess in the system or
> you'll get weirdness. For instance DMA initiated from the PCI bus at
> address 0, intended to read from SDRAM at 0 must not be claimed by
> another device on the PCI bus. IMHO, a 1:1 mapping between PCI and CPU
> is strongly preferred. Any other configuration will need some
> additional techniques to avoid aliasing.

Ah, good point. You are obviously right, it should definitely be a 1:1
mapping, anything else just creates a mess. I was working on a system
like that before, it wasn't pretty (you have to provide separate
dma_map_ops then).

	Arnd