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

[mchehab@infradead.org (Mauro Carvalho Chehab)]

Em 19-04-2011 03:08, Jiri Slaby escreveu:
> 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 ?roda 13 kwiecie? 2011 o 20:32:31 Russell King - ARM Linux 
>>> napisa?(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@suse.cz>
> Date:   Mon Feb 28 06:37:02 2011 -0300

It seems the better option for now.

Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>

> 
>     [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,