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From: Arnd Bergmann <arnd@arndb.de>
Date: Mon, 26 Jun 2017 22:43:40 +0200
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Subject: Re: [PATCH 2/7] iomap: implement ioread64 and iowrite64
To: Logan Gunthorpe <logang@deltatee.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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> +u64 ioread64(void __iomem *addr)
> +{
> +       u64 low, high;
> +
> +       low = ioread32(addr);
> +       high = ioread32(addr + sizeof(u32));
> +       return low | (high << 32);
> +}
> +u64 ioread64be(void __iomem *addr)
> +{
> +       u64 low, high;
> +
> +       low = ioread32be(addr + sizeof(u32));
> +       high = ioread32be(addr);
> +       return low | (high << 32);
> +}
> +#endif

This hardcodes the behavior of include/linux/io-64-nonatomic-hi-lo.h, which
I find rather confusing, as only about one in five drivers wants this
behavior.

I'd suggest you don't add it in lib/iomap.c at all for 32-bit architectures,
but rather use the same logic that we have for readq/writeq in
io-64-nonatomic-hi-lo.h and io-64-nonatomic-lo-hi.h, adding
{lo_hi,hi_lo}_{ioread,iowrite}{,be} to the same files, and provide
the {ioread,iowrite}{,be} macros only if they have not been defined
at that point.

       Arnd