Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16 with generic iowrite(read)8/16(be) | Date | Wed, 30 Jan 2013 15:36:10 +0100 |
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On Wednesday 30 January 2013 13:31:58 Michal Simek wrote: > Also from my understanding of arm we should use readl/b/w functions because > they have memory barriers which should be probably performed. > > And I haven't found any IO function which will behave on arm as LE and > on PPC as BE.
There are none, except for the __raw_ versions that are generally not recommended for other reasons.
There really is no easy solution, because most of the hardware IP blocks have fixed endianess, e.g. an OHCI USB controller will normally have little-endian registers on all architectures, but in very rare cases it may be big-endian, because some hardware designer tried to be helpful and put a byte swapping logic in front of it.
There are a few devices that tend to have the same endianess as the CPU, again because some hardware designer tried to make things easy for software by making the hardware confiurable. Again, what normally happens is that the next hardware designer takes this block and hardwires it to some endianess that he sees as "correct" but puts it on a system with a variable-endian CPU. Note that there are both little-endian PowerPC systems and big-endian ARM systems, they just happen to be the minority on an architecture where 99% of the users prefer the opposite.
The outcome is basically you're screwed for every driver that is not fixed endianess. The normal workaround is to do something like
#if defined(CONFIG_FOO_BIG_ENDIAN) && !defined(CONFIG_FOO_LITTLE_ENDIAN) /* always big-endian #define foo_readl(dev, reg) ioread32_be(dev->regs + reg) #define foo_writel(dev, reg, val) iowrite32_be(val, dev->regs + reg) #elif !defined(CONFIG_FOO_BIG_ENDIAN) && defined(CONFIG_FOO_LITTLE_ENDIAN) /* always little-endian #define foo_readl(dev, reg) ioread32(dev->regs + reg) #define foo_writel(dev, reg, val) iowrite32e(val, dev->regs + reg) #else /* run-time configured */ #define foo_readl(dev, reg) dev->readl(dev->regs + reg) #define foo_writel(dev, reg, val) dev->writel(val, dev->regs + reg) #endif
and select the CONFIG_FOO_BIG_ENDIAN and CONFIG_FOO_LITTLE_ENDIAN symbols in Kconfig based on the system you are building for.
This of course gets further complicated if you require different accessors per architecture, like ARM wanting readl or ioread32 and PowerPC wanting in_le32 for a little-endian SoC component.
Arnd
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