[PATCH] USB: set device dma_mask without reference to global data

[Alan Stern]

On Wed, 8 May 2013, Arnd Bergmann wrote:

> On Wednesday 08 May 2013, Greg Kroah-Hartman wrote:
> > On Tue, May 07, 2013 at 04:53:52PM -0600, Stephen Warren wrote:
> > > From: Stephen Warren <swarren at nvidia.com>
> 
> > > Suggested-by: Arnd Bergmann <arnd at arndb.de>
> > > Signed-off-by: Stephen Warren <swarren at nvidia.com>
> > 
> > So this needs to go in for 3.10, right?  Any older kernels as well?  If
> > so, which ones?
> 
> The fix should definitely go into 3.10, but I'd suggest waiting with
> the backport for a couple of -rc releases to avoid possible regressions.
> We know that the current code is broken, but few people fully understand
> what is going on with coherent_dma_mask, so it might cause new problems
> in combination with some other unknown bug, and I don't see this as
> urgent: none of the ARM defconfigs build this driver as a loadable
> module and there is no bug in the built-in case. For some reason, only
> the ARM back-end drivers are broken.
> 
> The first occurence was apparently in 3.3, but only in ehci-tegra.c,
> while the other drivers subsequently copied the bug.

An alternative solution -- perhaps not better but also not relying on
coherent_dma_mask -- is to clear pdev->dev.dma_mask in the remove
routine if it points to the static mask value.

Alan Stern