From: arnd@arndb•de (Arnd Bergmann)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/8] ARM: support for Moschip MCS814x SoCs
Date: Tue, 17 Jul 2012 13:12:06 +0000 [thread overview]
Message-ID: <201207171312.06987.arnd@arndb.de> (raw)
In-Reply-To: <20120717121640.589780ce@skate>
On Tuesday 17 July 2012, Thomas Petazzoni wrote:
> Le Mon, 16 Jul 2012 15:54:04 +0000,
> Arnd Bergmann <arnd@arndb•de> a ?crit :
>
> > > +void mcs814x_restart(char mode, const char *cmd)
> > > +{
> > > + __raw_writel(~(1 << 31), mcs814x_sysdbg_base);
> > > +}
> >
> > You should generally avoid using __raw_readl etc. and instead use
> > readl/write or readl_relaxed/writel_relaxed.
>
> I thought that readl/writel and readl_relaxed/writel_relaxed were used
> for PCI-style access, for which these macros/functions do automatically
> a conversion from the CPU-endianness to the PCI-endianness
> (little-endian). Here of course, this the SoC is used little-endian, it
> will just work because readl/writel will not do any endianness
> conversion, but if we were on a big-endian machine?
>
> My understanding until now was that __raw_readl/__raw_writel should be
> used for accesses with native endianness, but apparently, it's more
> subtle than this. Would you mind expanding a bit on this?
The __raw_* versions are basically only valid if you access a memory
buffer, such as a video framebuffer. They do the conversion of an
__iomem pointer into something that can be accessed by the compiler.
The non-raw versions have fixed endianess, guarantee that the access
is done atomically (could be byte-wise otherwise) and that all the
necessary barriers are used to synchronize against DMA and out-of-order
execution.
We don't actually have accessors that are CPU-endian and guarantee that
you can access an MMIO register properly.
On powerpc, the convention is that readl/writel should only be used
to access PCI, but that is for the enhanced error handling, not for
endianess.
Arnd
next prev parent reply other threads:[~2012-07-17 13:12 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-15 14:49 [PATCH 0/8] ARM: support for Moschip MCS814x SoCs Florian Fainelli
2012-07-15 14:49 ` [PATCH 1/8] " Florian Fainelli
2012-07-16 12:29 ` Thomas Petazzoni
2012-07-16 12:43 ` Florian Fainelli
2012-07-16 15:55 ` Arnd Bergmann
2012-07-16 17:57 ` Nicolas Pitre
2012-07-23 19:11 ` Florian Fainelli
2012-07-27 22:42 ` Linus Walleij
2012-07-16 15:54 ` Arnd Bergmann
2012-07-16 20:47 ` Turquette, Mike
2012-07-17 9:41 ` Florian Fainelli
2012-07-17 10:47 ` Florian Fainelli
2012-07-16 22:12 ` Linus Walleij
2012-07-17 9:35 ` Florian Fainelli
2012-07-17 9:34 ` Florian Fainelli
2012-07-17 13:07 ` Arnd Bergmann
2012-07-17 13:32 ` Florian Fainelli
2012-07-17 13:45 ` Arnd Bergmann
2012-07-17 10:16 ` Thomas Petazzoni
2012-07-17 13:12 ` Arnd Bergmann [this message]
2012-07-17 13:28 ` Thomas Petazzoni
2012-07-17 13:51 ` Arnd Bergmann
2012-07-16 22:06 ` Linus Walleij
2012-07-15 14:49 ` [PATCH 2/8] ARM: MCS814x: add Device Tree based MCS8140 board support Florian Fainelli
2012-07-17 13:19 ` Arnd Bergmann
2012-07-17 13:34 ` Florian Fainelli
2012-07-17 13:53 ` Arnd Bergmann
2012-07-17 13:57 ` Florian Fainelli
2012-07-15 14:49 ` [PATCH 3/8] ARM: MCS814x: add Device Tree bindings documentation Florian Fainelli
2012-07-17 13:24 ` Arnd Bergmann
2012-07-17 13:35 ` Florian Fainelli
2012-07-15 14:49 ` [PATCH 4/8] ARM: MCS814X: add DTS file for Tigal/Robotech RBT-832 Florian Fainelli
2012-07-17 13:27 ` Arnd Bergmann
2012-07-15 14:49 ` [PATCH 5/8] ARM: MCS814x: add DTS file for Devolo dLAN USB Extender Florian Fainelli
2012-07-15 14:49 ` [PATCH 6/8] ARM: MCS814x: provide a sample defconfig file Florian Fainelli
2012-07-15 14:49 ` [PATCH 7/8] ARM: MSC814X: add Kconfig and Makefile to arch/arm Florian Fainelli
2012-07-15 14:49 ` [PATCH 8/8] ARM: MSC814x: add MAINTAINERS entry Florian Fainelli
2012-07-15 19:59 ` [PATCH 0/8] ARM: support for Moschip MCS814x SoCs Arnd Bergmann
2012-07-16 8:16 ` Florian Fainelli
2012-07-16 18:09 ` Nicolas Pitre
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