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From: Rolf Offermanns on 1 Nov 2006 06:20
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

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From: Guillermo Marcus Martinez on 1 Nov 2006 08:00
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().

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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From: yogeshwar sonawane on 1 Nov 2006 09:10
On 11/1/06, Guillermo Marcus Martinez <marcus(a)ti.uni-mannheim.de> 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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From: Guillermo Marcus Martinez on 1 Nov 2006 10:10
yogeshwar sonawane schrieb:
> On 11/1/06, Guillermo Marcus Martinez <marcus(a)ti.uni-mannheim.de> 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.
>

I will give it a try. I guess it may not be equivalent to setting
VM_RESERVED before calling remap_page/pfn_range(). Is this platform
specific, or is intended behavior/usage of remap_page/pfn_range()?


>>
>> 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
>>
>> -
>> To unsubscribe from this list: send the line "unsubscribe
>> linux-kernel" in
>> the body of a message to majordomo(a)vger.kernel.org
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at http://www.tux.org/lkml/
>>
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From: Russell King on 2 Nov 2006 03:40
On Wed, Nov 01, 2006 at 01:58:17PM +0100, Guillermo Marcus Martinez wrote:
> 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.

You might want to look through include/asm-arm/dma-mapping.h to see if
an architecture already has considered that and the interface they
implemented.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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