linux-kernel - Re: [PATCH 3/7] asm-generic/io.h: make ioread64 and iowrite64 universally available

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Date:   Thu, 22 Jun 2017 14:24:58 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-ntb@...glegroups.com, linux-alpha@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-crypto@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH 3/7] asm-generic/io.h: make ioread64 and iowrite64
 universally available

On 6/22/2017 2:14 PM, Alan Cox wrote:
> If a platform doesn't support 64bit I/O operations from the CPU then you
> either need to use some kind of platform/architecture specific interface
> if present or accept you don't have one.

Yes, I understand that.

The thing is that every user that's currently using it right now is 
patching in their own version that splits it on non-64bit systems.

> It's not safe to split it. Possibly for some use cases you could add an
> ioread64_maysplit()

I'm open to doing something like that.

> What btw is the actual ARM compiler warning ? Is the compiler also trying
> to tell you it's a bad idea ?

It's just the compiler noting that you are mixing volatile and 
non-volatile pointers. Strangely some io{read|write}XX use volatile but 
most do not. But it's nothing crazy.

Logan