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    SubjectRe: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses
    On Fri, Jun 17, 2011 at 11:30:32AM +0200, Ingo Molnar wrote:
    > I'm aware of these current /dev/mem uses:
    >
    > - Xorg maps below 4G non-RAM addresses and the video BIOS
    >
    > - It used to have some debugging role but these days kexec and kgdb
    > has largely taken over that role - partly due to the 4G limit.
    >
    > - there's some really horrible out-of-tree drivers that do mmap()s
    > via /dev/mem, those should be fixed if they want to move beyond
    > 4G: their char device should be mmap()able.
    >
    > - all distro kernel's i'm aware of use CONFIG_STRICT_DEVMEM=y, which
    > restricts /dev/mem to non-RAM pages of physical memory.
    > [ With the sad inclusion of the first 1MB, which Xorg needs. ]

    There's another use case for /dev/mem:

    - debugging via devmem2 on embedded platforms, where you want to be able
    to boot a kernel, and then peek and poke at MMIO registers either to
    verify register values or test things out.


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