linux-kernel - Re: [PATCH v2 1/3] io-64-nonatomic: add io{read|write}64[be] macros

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Message-ID: <e32bd057-2069-63c9-b75d-3a97a736d898@deltatee.com>
Date:   Wed, 28 Jun 2017 10:02:57 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-ntb@...glegroups.com, linux-crypto@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jyri Sarha <jsarha@...com>,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v2 1/3] io-64-nonatomic: add io{read|write}64[be] macros



On 28/06/17 04:11 AM, Arnd Bergmann wrote:
> This is wrong since ioread* is not the same read* on x86 and other
> architectures that have native PCI PIO accessors, or that require
> additional barriers for those.
> 
> You have to copy hi_lo_readq() here, and call ioread32 twice instead
> of calling readl() twice. Same for iowrite64.
> 
>> +#ifndef ioread64be
>> +#define ioread64be(p) be64_to_cpu(ioread64(p))
>> +#endif
> 
> This has another problem: ioread64() is defined to access little-endian
> registers, just like readq(). This means that instead of be64_to_cpu()
> you need swab64() and always perform the byte swap, otherwise this
> would be broken on big-endian architectures.

Ah, ok, understood. I'll see if I can fix both these issues.

Thanks,

Logan