[alsa-devel] [PATCH 4/4] ASoC: fsl: make fsl_ssi driver compilable on ARM/IMX
timur at freescale.com
Fri Feb 24 22:29:04 CET 2012
Russell King - ARM Linux wrote:
>> > I'll have to ask around, because I'm sure I'm missing something.
> If what you say is true, it means we have different semantics for the
> same accessors on different architectures. No wonder it's needing
> drivers to gain ifdefs to select appropriate accessors.
> This needs sorting out properly. It needs the semantics of readl() etc
> to be fully defined, and all architectures to implement those semantics
> rather than what they think would be appropriate for them.
So I asked around, and sure enough, my macro-fu was weak. On PowerPC,
readl() maps to in_le32(). Even though PowerPC is big-endian, some
devices are little endian (e.g. PCI and some PICs).
in_le32() is the byte-swapping version of in_be32(). Both functions have
instruction order synchronization instructions in them.
So replacing in_be32() with readl() will break on PowerPC.
Linux kernel developer at Freescale
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