linux-imx

of: fix DMA mask generation

Historically, DMA masks have suffered some ambiguity between whether
they represent the range of physical memory a device can access, or the
address bits a device is capable of driving, particularly since on many
platforms the two are equivalent. Whilst there are some stragglers left
(dma_max_pfn(), I'm looking at you...), the majority of DMA code has
been cleaned up to follow the latter definition, not least since it is
the only one which makes sense once IOMMUs are involved.

In this respect, of_dma_configure() has always done the wrong thing in
how it generates initial masks based on "dma-ranges". Although rounding
down did not affect the TI Keystone platform where dma_addr + size is
already a power of two, in any other case it results in a mask which is
at best unnecessarily constrained and at worst unusable.

BCM2837 illustrates the problem nicely, where we have a DMA base of 3GB
and a size of 1GB - 16MB, giving dma_addr + size = 0xff000000 and a
resultant mask of 0x7fffffff, which is then insufficient to even cover
the necessary offset, effectively making all DMA addresses out-of-range.
This has been hidden until now (mostly because we don't yet prevent
drivers from simply overwriting this initial mask later upon probe), but
due to recent changes elsewhere now shows up as USB being broken on
Raspberry Pi 3.

Make it right by rounding up instead of down, such that the mask
correctly correctly describes all possisble bits the device needs to
emit.

Fixes: 9a6d7298b083 ("of: Calculate device DMA masks based on DT dma-range size")
Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
Reported-by: Andreas Färber <afaerber@suse.de>
Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>