On Wed, Feb 6, 2013 at 6:40 PM, Michal Simek <[email protected]> wrote:
> One question regarding to asm-generic/io.h about iowrite16be implementation
>
> #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.
> On little
> be16_to_cpu(v) is swab16(v)
Yes.
> and
> __cpu_to_le16(swab(b)) is swab16(v)
???
Don't you mean "__cpu_to_le16(b) is (b)"?
> 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)".
Same for iowrite32be().
> on Big endian:
> __cpu_to_be16(v) is (v)
> on Little endian:
> __cpu_to_be16(v) is swab(v)
>
> What am I missing here?
But as both conversions are identical (just swapping 2 bytes), It Just Works.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
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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