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    SubjectRe: can device drivers return non-ram via vm_ops->nopage?
    On Sat, 20 Mar 2004, Russell King wrote:

    > It is well known that virt_to_page() is only valid on virtual addresses
    > which correspond to kernel direct mapped RAM pages, and undefined on
    > everything else. Unfortunately, ALSA has been using it with
    > pci_alloc_consistent() for a long time, and this behaviour is what
    > makes ALSA broken. The fact it works on x86 is merely incidental.

    It works on PPC as well (at least we have no error reports).

    > If ALSA wants this functionality, the ALSA people should ideally have
    > put their requirements forward during the 2.5 development cycle so the
    > problem could be addressed.

    Yes, I'm sorry about that, but the ->nopage usage was requested by Jeff
    Garzik and we're not gurus for the VM stuff. Because we're probably first
    starting using of this mapping scheme, it resulted to problems.

    > However, luckily in this instance, it is not a big problem to solve.
    > It just requires time to sort through all the abstraction layers upon
    > abstraction layers which ALSA has.
    >
    > - and I'm doing exactly this, right now. Be patient. -

    Thanks a lot.

    Jaroslav

    -----
    Jaroslav Kysela <perex@suse.cz>
    Linux Kernel Sound Maintainer
    ALSA Project, SuSE Labs
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