[PATCH 2.6.39 v2] V4L: videobuf-dma-contig: fix mmap_mapper broken on ARM

[Janusz Krzysztofik]

Dnia czwartek 14 kwiecień 2011 o 00:00:08 Russell King - ARM Linux 
napisał(a):
> 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.
> 
> Do we even know whether bus_to_virt(iommu_bus_address) works?  I
> suspect it doesn't, so by doing so you're already re-breaking the
> IOMMU case.

Hard to deny with only me having actually tested this dirty hack on one 
single board :)

Thanks for your support,
Janusz