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

[Russell King - ARM Linux]

On Wed, May 08, 2013 at 09:24:44AM +0200, Arnd Bergmann wrote:
> It probably should. The main thing is that the dma_mask setting in
> of_platform (and elsewhere) is a mess and that nobody so far had the
> guts to try to get it right for good.
> 
> Setting a 32 bit DMA mask is /probably/ the right default on all
> ARM systems, but there are caveats:
> 
> - Once you get to systems with larger than 32 bit addressing (powerpc64,
>   arm64, arm32 with LPAE), it's not so obvious: you may have some devices
>   that need a 32 bit mask and some that need a 64 bit mask.

This is precisely why drivers should be using dma_set_mask() and the
coherent version to provide the mask for which the driver knows about
- iow, if the device itself is only capable of 32-bit DMA, then the
device must use dma_set_mask(dev, DMA_BIT_MASK(32)).