On Thursday 25 June 2015 15:01:56 Casey Leedom wrote:
>
> Is there a reference I can read on this so I can understand
> when and where we can use the __raw_*() APIs? Can these
> Raw Read/Write operations be reordered with respect to
> each other or are the use of the various flavors of SYNC
> instructions just to maintain order between Cached Memory
> Accesses and I/O Instructions?
The interpretation is not consistent across architectures.
My best description would be that the __raw_*() accessors should
only be used for accessing RAM areas that are known to have no
side-effects and can be read in any size (8-bit to 64-bit wide),
any alignment, and do not have a specific endianess.
If you are dealing with MMIO registers that have a fixed endianess
and size, the correct accessor would be readl_relaxed(), which
is like readl() but lacks the barriers on certain architectures.
Arnd
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