* Undestanding ioread32() / readl() and friends
@ 2007-02-21 9:50 Florian Boelstler
2007-02-21 9:56 ` Arnd Bergmann
0 siblings, 1 reply; 3+ messages in thread
From: Florian Boelstler @ 2007-02-21 9:50 UTC (permalink / raw)
To: linuxppc-embedded
Hi,
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?
BTW, "Linux Device Drivers, 3rd edition" by Corbet et al states that
ioread32() does not perform any endian conversion.
May be they are based on x86...
Thanks,
Florian
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Undestanding ioread32() / readl() and friends
2007-02-21 9:50 Undestanding ioread32() / readl() and friends Florian Boelstler
@ 2007-02-21 9:56 ` Arnd Bergmann
2007-02-21 14:33 ` Florian Boelstler
0 siblings, 1 reply; 3+ messages in thread
From: Arnd Bergmann @ 2007-02-21 9:56 UTC (permalink / raw)
To: linuxppc-embedded
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 <><
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Undestanding ioread32() / readl() and friends
2007-02-21 9:56 ` Arnd Bergmann
@ 2007-02-21 14:33 ` Florian Boelstler
0 siblings, 0 replies; 3+ messages in thread
From: Florian Boelstler @ 2007-02-21 14:33 UTC (permalink / raw)
To: linuxppc-embedded
Hi,
Arnd Bergmann schrieb:
>> 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.
OK, my knowledge about ioread32() was based on some explanations found
in "Linux Device Drivers". IMHO they showed the ioread family of
functions as a sort of general purpose functions for __iomem-alike
resources.
Thanks, anyway.
Florian
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2007-02-21 14:33 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2007-02-21 9:50 Undestanding ioread32() / readl() and friends Florian Boelstler
2007-02-21 9:56 ` Arnd Bergmann
2007-02-21 14:33 ` Florian Boelstler
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox