Re: [PATCH] powerpc: Fix problems with 32bit PPC's running with more than 2GB of RAM

On Jul 9, 2008, at 7:44 PM, Josh Boyer wrote:

On Thu, 10 Jul 2008 06:39:39 +1000
Benjamin Herrenschmidt [off-list ref] wrote:

quoted

On Wed, 2008-07-09 at 16:22 -0400, Josh Boyer wrote:

quoted

On Thu, 10 Jul 2008 06:02:38 +1000
Benjamin Herrenschmidt [off-list ref] wrote:

quoted

On Wed, 2008-07-09 at 15:44 +0200, Stefan Roese wrote:

quoted

This patch enables 32bit PPC's (with 36bit physical address  
space, e.g.
IBM/AMCC PPC44x) to run with more than 2GB of RAM. Mostly its just
replacing types (unsigned long -> phys_addr_t).

Tested on an AMCC Katmai with 4GB of DDR2.

Signed-off-by: Stefan Roese <sr@denx.de>

But DMAs will break no ?

How?

Hrm... forget it. It's fine up to 4G of RAM... (ie. as long as DMA is
below 32 bits).

Right.  We haven't really dealt with anything larger than 4 GiB, and  
we
certainly aren't dealing with discontiguous DRAM due to I/O ranges.

Are you *sure* you can see all 4GB?  I thought we lost some of the 32- 
bit PCI address space for PCI IO......  Disclaimer: I'm no expert on  
PCI :)

FYI, I'm *very* close to having swiotlb fully functional on powerpc to  
support larger RAM - I am able to boot with 6GB on 8641 right now.   
There are some bugs that I'm still shaking out - I hope to push this  
out in the next couple of weeks.

Cheers,
B