On 02/10/2019 05:17 PM, Andre Przywara wrote:
The normal MMIO accessor macros (readX/writeX) guarantee a strong ordering,
even with normal memory accesses: https://lwn.net/Articles/698014/
For some MMIO operations (framebuffers being a prominent example) this is
not needed, and the rather costly barrier inserted on weakly ordered
systems like ARM costs some performance.
To mitigate this issue, Linux introduced readX_relaxed and
writeX_relaxed primitives, which only guarantee ordering between each
other, so are typically faster due to the missing barrier.
We probably do not care so much about performance in U-Boot, but want to
have those primitives for two other reasons:
- Being able to use the _relaxed macros simplifies porting drivers from
Linux.
- The missing barrier typically allows to generate smaller code, which can
relieve some chronically tight SPL builds.
Add those macros definitions by using the __raw versions of the
accessors, which matches an earlier (and less complicated) version of
the Linux implementation.
Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
Reviewed-by: Philipp Tomsich <philipp.toms...@theobroma-systems.com>
[On my experimental RK3399 after modifying a few drivers:]
Tested-by: Philipp Tomsich <philipp.toms...@theobroma-systems.com>
Reviewed-by: Alexander Graf <ag...@suse.de>
Alex
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