Messages in this thread | | | Date | Mon, 19 May 2003 14:25:35 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: PCI mapping on large memory 32-bit machines |
| |
On Mon, 19 May 2003, Timothy Miller wrote:
> On x86 with PAE and 4 gigs of RAM or more, where do memory-mapped I/O > devices get mapped (in the physical address space)? Most PCI devices > can't handle 64-bit addresses. Can PC chipsets physically remap some of > the RAM to above 4 gig? Or do you just lose that much RAM? If both RAM > and some I/O device are mapped to the same location, isn't there a conflict? >
The answer to PC/PCI is that the I/O space set (usually by the BIOS) into the BARs removes any RAM visibility in that area. But.... this is BAD bacause the BIOS may still claim that there is 4 gig of RAM. The OS may then try to use it. To "solve" this problem, Win/tell started the "high-RAM" specification where RAM higher than XXX Megs gets mapped with page-registers. The problem is that "XXX" is board-specific!
So, to answer your entire question... don't do it! Only use 3 gigs max and you will not be confused by confused hardware!
Cheers, Dick Johnson Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips). Why is the government concerned about the lunatic fringe? Think about it.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |