On Thursday 17 July 2014 19:19:15 Peter Chen wrote:

Currently, we are designing a generic driver, we don't know what's the
hardware architecture, we are trying to find a solution how to set
dma mask for all possible devices which will use this driver, Antoine's
this patch is trying to cover this feature.

For example, 

Marvell Berlin doesn't need to set dma mask specific.
http://marc.info/?l=linux-arm-kernel&m=140205228507045&w=2
http://www.spinics.net/lists/linux-usb/msg110598.html

Xilinx zynq needs to set dma mask as 0xFFFFFFF0
http://marc.info/?l=linux-usb&m=140384129921706&w=2

FSL i.mx needs to set dma mask as DMA_BIT_MASK(32)
https://git.kernel.org/cgit/linux/kernel/git/gregkh/usb.git/tree/drivers/usb/chipidea/ci_hdrc_imx.c?h=usb-next

Ok, I see now. I think we can safely drop it completely then:

- Berlin was only recently added and doesn't need to set the
  mask because the common code handles it just fine now.

- i.mx was added earlier, at a time where it was still necessary

- zynq just made a mistake, 0xFFFFFFF0 was never a valid mask
  and just happened to work by accident.

In summary, the 32-bit default mask will work on all of them,
and we need no special code or DT properties for it.

	Arnd