lkml.org 
[lkml]   [2003]   [May]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: 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/

    \
     
     \ /
      Last update: 2005-03-22 13:35    [W:0.021 / U:30.280 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site