lkml.org 
[lkml]   [1998]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: 64 bit PCI and Linux
    Hello,

    > > - On 32-bit machines it's just able to read the 64 bit address and
    > > throws out the device if it's been configured by the BIOS to use
    > > addresses outside the 32 bit range the machine can handle.
    >
    > Why such a software limitation?

    I was wrong. We just ignore the 64-bit addresses and issue a warning. On the
    other hand, this will probably not appear in any real situation -- do you know
    of any machine where the CPU is 32 bit, but the firmware assigns 64 bit
    addresses to PCI devices?

    > The same scheme can be used for a 64 bit device on 64 bit PCI bus driven
    > from a 32 bit CPU and AFAIK, the Pentia II allows 36 bit addressing for
    > host memory. So, 64 bit PCI could be used on ia32 in order to DMA into the
    > whole 36 bit address range.

    The 36 bit addressing in P-II is a gross hack and it probably cannot be
    supported by any OS in a non-ugly way. There was a lengthy debate regarding
    this topic on linux-kernel some weeks ago and most people aggreed on "use
    a real 64 bit machine if you want more than 4G of address space".

    | I personally think solution 2) is kinda nifty, we could then implement
    | some DMA mapping functions like pci_map_bus() and pci_unmap_bus() and
    | let these be dummy functions on architectures who do not know how to
    | deal with it and 32 bits archs. It will definately make it easier for
    | the individual driver programmers.

    If setting up an IOMMU mapping is not too costly, I would prefer functions
    for remapping a DMA buffer to lower 4G and unmapping it which would be called
    before and after each DMA transfer.

    Have a nice fortnight
    --
    Martin `MJ' Mares <mj@ucw.cz> http://atrey.karlin.mff.cuni.cz/~mj/
    Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
    "A LISP programmer knows value of everything, but cost of nothing."

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.rutgers.edu
    Please read the FAQ at http://www.altern.org/andrebalsa/doc/lkml-faq.html

    \
     
     \ /
      Last update: 2005-03-22 13:44    [W:2.400 / U:0.220 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site