From: Arnd Bergmann <arnd@arndb.de>
To: linuxppc-embedded@ozlabs.org
Subject: Re: Undestanding ioread32() / readl() and friends
Date: Wed, 21 Feb 2007 10:56:27 +0100 [thread overview]
Message-ID: <200702211056.28313.arnd@arndb.de> (raw)
In-Reply-To: <erh4m0$n83$1@sea.gmane.org>
On Wednesday 21 February 2007 10:50, Florian Boelstler wrote:
> I just came across include/asm-ppc/io.h, which revealed that ioread32()
> maps to readl(), which in turn maps to in_le32() (when CONFIG_APUS and
> CONFIG_8260_PCI9 are both not defined).
> in_le32() uses a asm instruction lwbrx to do byte swapping.
>
> I don't really get why ioread32() effectively returns a little-endian
> value on a big-endian PPCs.
>
> Is this a sort of general rule that ioread32() always returns
> little-endian values on all architectures?
the ioread family of functions is used for PCI devices, which
are little-endian by definition.
If you want to access on-chip devices that are not behind PCI,
you should use the in_be family of functions.
Arnd <><
next prev parent reply other threads:[~2007-02-21 9:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-21 9:50 Undestanding ioread32() / readl() and friends Florian Boelstler
2007-02-21 9:56 ` Arnd Bergmann [this message]
2007-02-21 14:33 ` Florian Boelstler
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