On 05/14/2015 02:03 PM, Timur Tabi wrote:
On 05/14/2015 03:45 PM, Guenter Roeck wrote:
It concerns me that you point to other drivers as argument for using the
endianness conversion your code. That raises the question if you really
understand the hardware.
The only information I have on how the hardware works is the SBSA document and the internal documentation for our ARM64 server chip.
> Is the register known to be a little endian register,
even on a big endian machine, or is it in host byte order ? You don't really
answer that question.
The ARM SBSA says in section 4.1.1:
* CPUs shall implement little-endian support.
That doesn't really say anything. It neither says that the CPU must _run_
in little endian mode, nor does it say anything about its register byte order.
That's the only reference to endianness in the document. I don't know if that means that the device registers must also be little-endian. Does Linux even support running ARM64 in big-endian mode?
Interesting question. You should be able to answer it yourself.
Hint: Look in arch/arm64/Kconfig.
So maybe it's safe to say that everything must be little endian? If so, do I still need the __le32 in the structs, and should I still use cpu_to_le32()?
We still don't know if the registers are in host byte order or in little endian
order. If registers are in host byte order, there is no need for a conversion.
Guenter
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