Re: [PATCH 4/7] alpha: provide ioread64 and iowrite64 implementations

From: Arnd Bergmann
Date: Thu Jun 22 2017 - 17:03:31 EST

On Thu, Jun 22, 2017 at 10:09 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:
> On 6/22/2017 2:08 PM, Alan Cox wrote:
>> But this does not do the same thing as an ioread64 with regards to
>> atomicity or side effects on the device. The same is true of the other
>> hacks. You either have a real 64bit single read/write from MMIO space or
>> you don't. You can't fake it.
> Yes, I know. But is it not better than having every driver that wants to use
> these functions fake it themselves?

Drivers that want a non-atomic variant should include either
include/linux/io-64-nonatomic-hi-lo.h or include/linux/io-64-nonatomic-lo-hi.h
depending on what they need. Drivers that require 64-bit I/O should
probably just depend on CONFIG_64BIT and maybe use readq/writeq.

I see that there are exactly two drivers calling ioread64/iowrite64:
drivers/crypto/caam/ is architecture specific and
drivers/ntb/hw/intel/ntb_hw_intel.c already has a workaround that should
make it build on alpha.