[PATCH V2 1/3] scsi: mptxsas: try 64 bit DMA when 32 bit DMA fails

On Tuesday 10 November 2015 11:00:59 Timur Tabi wrote:

On 11/10/2015 10:47 AM, Arnd Bergmann wrote:

quoted

What BenH was worried about here is that the driver sets different masks
for streaming and coherent mappings, which is indeed a worry that
could hit us on ARM as well, but I suppose we'll have to deal with
that in platform code.

Setting both masks to 32-bit is something that a lot of drivers do,
and without IOMMU enabled, you'd hit the same bug on all of them.

Also note that I think that on PowerPC, the mask is set to 32 by default 
for all devices.  I don't think we do that on ARM64.  So on PowerPC, 
some drivers get away with not explicitly setting the mask.

If the mask is 64-bit by default on ARM64, that is a bug that we need
to fix urgently. Can you verify this?

A lot of PCI devices can only do 32-bit DMA, and we have plenty
of drivers that don't bother setting a mask at all because the 32-bit
mask is the default on all other architectures.

	Arnd