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    SubjectRe: how to use TLB to prevent Linux accessing a particular memory region

    On Tue, 16 Oct 2007, veerasena reddy wrote:

    > Hi,
    > I have a board, which has two processors ( one is MIPS
    > on which Linux-2.6.18 kernel runs and another is DSP
    > based processor) and 32MB DDR.
    > Out of 32MB of DDR 8MB is reserved for use by DSP
    > processor. But the MIPS processor downloads firmware
    > into this reserved memory for the DSP.
    > Now, is it possible to use the TLB to prevent Linux
    > from accessing the reserved memory after the firmware
    > has been downloaded?
    > Also we'd need to remove those TLB entries if the
    > firmware would ever need to be reloaded to the DSP'
    > memory region.
    > What are the APIs to be used to achieve the above?
    > Thanks in advance.
    > Regards,
    > Veerasena.
    > 5, 50, 500, 5000 - Store N number of mails in your inbox. Go to
    > -

    Can't you just memory-map the area you need? That reserves it
    until it's unmapped. You don't need to directly touch the TLB.
    If you need a physical location, use ioremap_nocache() in your
    driver. If you can't get your physical location because the
    kernel already uses it, boot the kernel with mem=xxx on the
    command-line to prevent the kernel from using memory you
    want to reserve for your DSP. You can use num_physpages
    (an integer) to find out the last page the kernel uses.

    BTW, if this is a new design, most DSP devices put their
    RAM on their own board so you don't have these problems.
    That RAM gets mmaped to user-space as needed for access,
    that address being set asside in PCI space.

    Dick Johnson
    Penguin : Linux version on an i686 machine (5592.59 BogoMips).
    My book :

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