On 2018-03-21 19:03, Casey Leedom wrote:
[[ Appologies for the DUPLICATE email. I forgot to tell my Mail Agent
to
use Plain Text. -- Casey ]]
I feel very uncomfortable with these proposed changes. Our team is
right
in the middle of trying to tease our way through the various platform
implementations of writel(), writel_relaxed(), __raw_writel(), etc. in
order
to support x86, PowerPC, ARM, etc. with a single code base. This is
complicated by the somewhat ... "fuzzily defined" semantics and varying
platform implementations of all of these APIs. (And note that I'm just
picking writel() as an example.)
Additionally, many of the changes aren't even in fast paths and are
thus
unneeded for performance.
Please don't make these changes. We're trying to get this all sussed
out.
I was also given the feedback to look at performance critical path only.
I am in the process of revisiting the patches.
If you can point me to the ones that are important, I can try to limit
the changes to those only.
If your team wants to do it, I can drop this patch as well.
I think the semantics of write API is clear. What was actually
implemented is another story.
I can share a few of my findings.
A portable driver needs to do this.
descriptor update in mem
wmb ()
writel_relaxed ()
mmiowb ()
Using __raw_write() is wrong as it can get reordered.
Using wmb()+writel() is also wrong for performance reasons.
If something is unclear, please ask.
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