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

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):

quoted

On Wed, Apr 13, 2011 at 12:52:31PM +0200, Janusz Krzysztofik wrote:

quoted

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.