linux-kernel - Re: [PATCH 2/7] iomap: implement ioread64 and iowrite64

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Date:   Mon, 26 Jun 2017 22:43:40 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     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>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Suresh Warrier <warrier@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH 2/7] iomap: implement ioread64 and iowrite64

> +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