[REVERT] Re: V4L: videobuf-dma-contig: fix mmap_mapper broken on ARM

[Jiri Slaby]

On 04/14/2011 12:00 AM, Russell King - ARM Linux wrote:
> On Wed, Apr 13, 2011 at 10:56:39PM +0200, Janusz Krzysztofik wrote:
>> Dnia środa 13 kwiecień 2011 o 20:32:31 Russell King - ARM Linux 
>> napisał(a):
>>> On Wed, Apr 13, 2011 at 12:52:31PM +0200, Janusz Krzysztofik wrote:
>>>> Taking into account that I'm just trying to fix a regression, and
>>>> not invent a new, long term solution: are you able to name an ARM
>>>> based board which a) is already supported in 2.6.39, b) is (or can
>>>> be) equipped with a device supported by a V4L driver which uses
>>>> videobuf- dma-config susbsystem, c) has a bus structure with which
>>>> virt_to_phys(bus_to_virt(dma_handle)) is not equal dma_handle?
>>>
>>> I have no idea - and why should whether someone can name something
>>> that may break be a justification to allow something which is
>>> technically wrong?
>>>
>>> Surely it should be the other way around - if its technically wrong
>>> and _may_ break something then it shouldn't be allowed.
>>
>> In theory - of course. In practice - couldn't we now, close to -rc3, 
>> relax the rules a little bit and stop bothering with something that may 
>> break in the future if it doesn't break on any board supported so far (I 
>> hope)?
> 
> If we are worried about closeness to -final, then what should happen is
> that the original commit is reverted; the "fix" for IOMMUs resulted in
> a regression for existing users which isn't trivial to resolve without
> risking possible breakage of other users.

Hi, as -rc4 is out, I think it's time to revert that commit and rethink
the mmap behaviour for some of next -rc1s.

Linus, please revert
commit 35d9f510b67b10338161aba6229d4f55b4000f5b
Author: Jiri Slaby <jslaby at suse.cz>
Date:   Mon Feb 28 06:37:02 2011 -0300

    [media] V4L: videobuf, don't use dma addr as physical
===

It fixes mmap when IOMMU is used on x86 only, but breaks architectures
like ARM or PPC where virt_to_phys(dma_alloc_coherent) doesn't work. We
need there dma_mmap_coherent or similar (the trickery what
snd_pcm_default_mmap does but in some saner way). But this cannot be
done at this phase.

thanks,
-- 
js
suse labs