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Subject: Re: [PATCH v3 18/18] infiniband: cxgb4: Eliminate duplicate barriers
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From: Sinan Kaya <okaya@codeaurora.org>
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Date: Sat, 17 Mar 2018 00:03:05 -0400
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On 3/16/2018 11:40 PM, Sinan Kaya wrote:
> I'll change writel_relaxed() with __raw_writel() in the series like you suggested
> and also look at your other comments.

I spoke too soon.

Now that I realized, code needs to follow one of the following patterns for correctness

1)
wmb()
writel()/writel_relaxed()

or 

2)
wmb()
__raw_wrltel()
mmiowb()

but definitely not

wmb()
__raw_wrltel()

Since #1 == #2, I'll stick to my current implementation of writel_relaxed()

Changing writel() to writel_relaxed() or __raw_writel() isn't enough. PowerPC needs mmiowb()
for correctness. ARM's mmiowb() implementation is empty.

So, there is no one size fits all solution with the current state of affairs.


-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.