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

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Date:   Thu, 22 Jun 2017 23:03:17 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-ntb@...glegroups.com, linux-alpha@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-crypto@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stephen Bates <sbates@...thlin.com>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>
Subject: Re: [PATCH 4/7] alpha: provide ioread64 and iowrite64 implementations

On Thu, Jun 22, 2017 at 10:09 PM, Logan Gunthorpe <logang@...tatee.com> 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.

        Arnd