linux-kernel - Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)

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Date:	Thu, 7 Feb 2013 08:38:53 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Michal Simek <monstr@...str.eu>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...retlab.ca>,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	dahinds@...rs.sourceforge.net
Subject: Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16
 with generic iowrite(read)8/16(be)

On Thu, Feb 7, 2013 at 8:23 AM, Michal Simek <monstr@...str.eu> wrote:
>>> #define iowrite16be(v, addr)   iowrite16(be16_to_cpu(v), (addr))
>>> #define iowrite16(v, addr)      writew((v), (addr))
>>> #define writew(b,addr) __raw_writew(__cpu_to_le16(b),addr)
>>>
>>> static inline void __raw_writew(u16 b, volatile void __iomem *addr)
>>> {
>>>         *(volatile u16 __force *) addr = b;
>>> }
>>>
>>> How is this suppose to work on Big Endian?
>>> be16_to_cpu(v) is (v)
>>> and
>>> __cpu_to_le16(b) is swab16(v)
>>
>> Yes.
>
> But on native BE system ( I expect that v is in big endian)
> iowrite16be(v, addr) should be just *(volatile u16 __force *) addr =
> v; not *(volatile u16 __force *) addr = swab16(v);

>>> What I would expect is
>>> #define iowrite16be(v, addr)   __raw_writew(__cpu_to_be16(v), addr)
>>
>> Indeed, it should be "__cpu_to_be16(v)" instead of "be16_to_cpu(v)".
>
> What do you mean by that?

Bummer, I missed that current iowrite16be() uses (the little endian)
iowrite16(),
not _raw_writew(), and thought the only difference between the original
and your version was the endianness conversion macro.

Yes,

    #define iowrite16be(v, addr)   __raw_writew(__cpu_to_be16(v), addr)

should be correct.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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