FSL 64-bit DMA window question

[Zang Roy-R61911]

> -----Original Message-----
> From: Benjamin Herrenschmidt [mailto:benh at kernel.crashing.org]
> 
> On Fri, 2013-06-07 at 07:58 +0000, Zang Roy-R61911 wrote:
> >
> > > -----Original Message-----
> > > From: Benjamin Herrenschmidt [mailto:benh at kernel.crashing.org]
> > >
> > > Hi Folks !
> > >
> > > Is there any specific reason why you chose 1T (40 bit) as the
> location of
> > > the 64-bit DMA window ?
> > >
> > > It happens that most current radeon adapters cannot DMA there, they
> have
> > > a 40-bit DMA limit. I seem to be getting things to work fine using a
> 39-
> > > bit window, but I suppose that might collide with something else ?
> > T4240 has 40bit physical address ability.
> > "
> > This chip's 40-bit, physical address map consists of local space and
> external address
> > space. For the local address map, 32 local access windows (LAWs) define
> mapping
> > within the local 40-bit (1 TB) address space. Inbound and outbound
> translation windows
> > can map the chip into a larger system address space such as the RapidIO
> or PCIe 64-bit
> > address environment. This functionality is included in the address
> translation and
> > mapping units (ATMUs).
> >
> > "
> > That should be the reason to set the DMA window to 40-bit.
> I see. However if the top half of that space isn't used by default with
> whatever is our current setup, it makes sense to move down the 64-bit
> DMA window to allow those adapters to function don't you think ?
Good to me.
40 bit DMA will prevent your radeon video card from working. Right?
Your P5020 DS system only support 36 bit physical address.

> 
> I'm trying to turn those FSL boxes into nice ppc64 dev. workstations :-)
That is good. I'd like to see how long it will build a kernel ...
thanks.
Roy