On 11/1/06, Guillermo Marcus Martinez <[email protected]> wrote:
Rolf Offermanns schrieb:
> Guillermo Marcus <marcus <at> ti.uni-mannheim.de> writes:
>> Note: I am using kernel 2.6.9 for these tests, as it is required by my
>> current setup. Maybe this issue has already been addressed in newer
>> kernel. If that is the case, please let me know.
>
> Have a look at this article:
>
> "The evolution of driver page remapping"
> http://lwn.net/Articles/162860/
>
> It should make things clearer.
>
> The "API changes in the 2.6 kernel series" page is also a very good read:
> http://lwn.net/Articles/2.6-kernel-api/
>
> HTH,
> Rolf
Thanks for the links!
Yes, it looks like a step in the right direction. However, the article
says about vm_insert_page(): "...What it does require is that the page
be an order-zero allocation obtained for this purpose...", therefore
making it also unusable for this case (mmaping a pci_alloc_consistent).
I think the limitation (being order zero), is related to the page
counting, as I understand that for bigger order allocations, only the
first-page counter is incremented (not every page). If that is a
problem, I guess I would also see a problem with my workaround, and I
see none (yet). So I may try in a newer kernel and see if I can use it
to walk the pages on the mmap without using the nopage().
Setting 'PG_reserved' bit of all allocated pages & then calling
remap_page/pfn_range()
will do the things for 2.6.9.
My suggestion would be to add two functions: pci_map_consistent() and
dma_map_coherent() to address this issue, and their corresponding
unmap's. That will make sure all that is needed is done, is a clean and
consistent with the pci_ and dma_ APIs, and fills a mmap requirement not
covered by the other functions.
Best wishes,
Guillermo
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