linux-kernel - Re: [RESEND PATCH 2/4] asm-generic: io: don't perform swab during {in,out} string functions

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Date:	Wed, 17 Oct 2012 21:16:10 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Will Deacon <will.deacon@....com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Mike Frysinger <vapier@...too.org>,
	Ben Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RESEND PATCH 2/4] asm-generic: io: don't perform swab during
 {in,out} string functions

On Wed, Oct 17, 2012 at 5:45 PM, Will Deacon <will.deacon@....com> wrote:
> The {in,out}s{b,w,l} functions are designed to operate on a stream of
> bytes and therefore should not perform any byte-swapping, regardless of
> the CPU byte order.

Euh?

They transfer a stream of bytes between memory and PCI/ISA I/O space by
reading from/writing to a single I/O port of width 8, 16, or 32 bits.
On big endian machines, I/O port accesses may need to be swapped.

> This patch fixes the generic IO header so that {in,out}s{b,w,l} call
> the __raw_{read,write} functions directly rather than going via the
> endian-correcting accessors.

Furthermore __raw_*() has different semantics besides endianness, like
ordering barriers. So you can't just change one for the other.

> Cc: Mike Frysinger <vapier@...too.org>
> Cc: Ben Herrenschmidt <benh@...nel.crashing.org>
> Acked-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  include/asm-generic/io.h |   12 ++++++------
>  1 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> index 3607921..403b861 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -148,7 +148,7 @@ static inline void insb(unsigned long addr, void *buffer, int count)

The "addr" parameter is actually a misnomer. Probably it should be "port".
Oops, inb() and friends also use "addr".

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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