lkml.org 
[lkml]   [1997]   [Jun]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: pre2.0.31-2
    On Wed, 4 Jun 1997, Leonard N. Zubkoff wrote:

    > From: alan@lxorguk.ukuu.org.uk (Alan Cox)
    > Date: Wed, 4 Jun 1997 20:30:21 +0100 (BST)
    >
    > > 1) The memory mapped by 'vremap' is marked cacheable. This
    > > is (almost certainly) incorrect as it is memory that is
    > > actually device memory. Note that the mmap call used by
    > > X servers marks the memory as uncached.
    >
    > The PC architecture is supposed to handle this for you. It could well
    > be an issue on MIPS and friends. The X one is hack and shouldnt be needed
    >
    > Indeed, I recall reading somewhere in the 440FX Natoma (or 430HX) chipset
    > documentation that there was no caching on any PCI memory accesses.

    last i recall the mechanizm is two-sided, once there are possible MTTR
    settings for a memory area, second there is the caching bit in the page
    table entry. The CPU uses the worst setting.

    so if you have a BIOS that say sets some more clever MTTR value for
    certain memory ranges, it might make a difference wether you set the page
    table entry caching or nocaching. [there was one report that
    ioremap_nocache() on 2.1 made difference on a high end device driver.]

    -- mingo


    \
     
     \ /
      Last update: 2005-03-22 13:39    [W:0.018 / U:125.244 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site