memcpy alignment for DEVICE_nGnRnE

[mbohan@codeaurora.org (Michael Bohan)]

On Tue, Apr 08, 2014 at 12:49:49PM +0100, Catalin Marinas wrote:
> On Tue, Apr 08, 2014 at 01:35:47AM +0100, Michael Bohan wrote:
> > How should we handle Device Memory with copy_from_user / copy_to_user?
> > Should we follow the same scheme and create
> > copy_from_user_io / copy_to_user_io, or rather enforce that the stock
> > routines handle alignment?
> 
> We have generic copy_from_user_toio() and copy_to_user_fromio(). Are
> these what you need? As with the memcpy_(to|from)io, they can be further
> optimised.

It seems these existing routines are in sound. Were you thinking
the right approach would be to move them out of sound and make
them per-arch defined?

What about the other two use cases: copy_from_user_fromio and
copy_to_user_toio? Are those reasonable to add? These two APIs
would cover the use case I had in mind.

Then what about the strange but possible use case where both the
source and destination pointers are iomem? This same question
applies for memcpy_fromio / memcpy_toio as well.

The implementations of copy_from_user_toio and
copy_to_user_fromio are currently doing a second copy, so that
seems bad for performance. We'd probably want to improve these as
well if others are in agreement.

Thanks,
Mike
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