* PCI mapping on large memory 32-bit machines
@ 2003-05-19 18:15 Timothy Miller
2003-05-19 18:25 ` Richard B. Johnson
2003-05-19 22:59 ` William Lee Irwin III
0 siblings, 2 replies; 3+ messages in thread
From: Timothy Miller @ 2003-05-19 18:15 UTC (permalink / raw)
To: Linux Kernel Mailing List
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?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: PCI mapping on large memory 32-bit machines
2003-05-19 18:15 PCI mapping on large memory 32-bit machines Timothy Miller
@ 2003-05-19 18:25 ` Richard B. Johnson
2003-05-19 22:59 ` William Lee Irwin III
1 sibling, 0 replies; 3+ messages in thread
From: Richard B. Johnson @ 2003-05-19 18:25 UTC (permalink / raw)
To: Timothy Miller; +Cc: Linux Kernel Mailing List
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.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: PCI mapping on large memory 32-bit machines
2003-05-19 18:15 PCI mapping on large memory 32-bit machines Timothy Miller
2003-05-19 18:25 ` Richard B. Johnson
@ 2003-05-19 22:59 ` William Lee Irwin III
1 sibling, 0 replies; 3+ messages in thread
From: William Lee Irwin III @ 2003-05-19 22:59 UTC (permalink / raw)
To: Timothy Miller; +Cc: Linux Kernel Mailing List
On Mon, May 19, 2003 at 02:15:23PM -0400, 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?
AFAIK most (if not all) of that lands below 4GB in extant chipsets/BIOS's.
Remapping above 4GB is possible but various things would probably barf.
-- wli
^ permalink raw reply [flat|nested] 3+ messages in thread
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2003-05-19 18:25 ` Richard B. Johnson
2003-05-19 22:59 ` William Lee Irwin III
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