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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 Kysela <>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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