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    SubjectRe: [PATCH 05/14] lib: Add I/O map cache implementation
    On Wed, Jan 09, 2013 at 09:43:05PM +0100, Thierry Reding wrote:
    > The I/O map cache is used to map large regions of physical memory in
    > smaller chunks to avoid running out of vmalloc()/ioremap() space.
    >
    > Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>

    We already have a means where we record the mappings which ioremap()
    creates. If you look at /proc/vmallocinfo, you'll notice lines such
    as:

    0xf7b72000-0xf7b74000 8192 e1000_probe+0x291/0xa68 [e1000e] phys=fc025000 ioremap

    which gives you the virtual address range, physical address and type
    of the mapping. Why do we need a duplicated data structure?

    Moreover, you seem to suggest that you want to break up a large
    ioremap() mapping into several smaller mappings. Why? The idea
    behind ioremap() is that this relationship holds true:

    ptr = ioremap(cookie + n, size);

    For any 'n' in the range 0 .. size, the location shall be accessible
    via ptr + n when using the IO space accessors. If you're going to
    break up a mapping into several smaller ones, this no longer holds
    true.

    If the problem is that you're ioremapping huge address ranges because
    you're passing larger-than-required resources to devices, then that's
    part of the problem too.


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