From: Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [PATCH 3/7] asm-generic/io.h: make ioread64 and iowrite64
 universally available
Date: Thu, 22 Jun 2017 14:38:28 -0600
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To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
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On 6/22/2017 2:36 PM, Alan Cox wrote:
> I think that makes sense for the platforms with that problem. I'm not
> sure there are many that can't do it for mmio at least. 486SX can't do it
> and I guess some ARM32 but I think almost everyone else can including
> most 32bit x86.
>
> What's more of a problem is a lot of platforms can do 64bit MMIO via
> ioread/write64 but not 64bit port I/O, and it's not clear how you
> represent that via an ioread/write API that abstracts it away.

In Patch 2, we call bad_io_access for anyone trying to do 64bit accesses 
on port I/O.

Logan