linux-kernel - Re: [PATCH v2 16/18] x86: io: implement dummy relaxed accessor macros for writes

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Message-ID: <537E30AF.4070501@zytor.com>
Date:	Thu, 22 May 2014 10:15:27 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Will Deacon <will.deacon@....com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	arnd@...db.de, monstr@...str.eu, dhowells@...hat.com,
	broonie@...aro.org, benh@...nel.crashing.org, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 16/18] x86: io: implement dummy relaxed accessor macros
 for writes

On 05/22/2014 09:47 AM, Will Deacon wrote:
> write{b,w,l,q}_relaxed are implemented by some architectures in order to
> permit memory-mapped I/O accesses with weaker barrier semantics than the
> non-relaxed variants.
> 
> This patch adds dummy macros for the read and write accessors to x86,
> which simply expand to the non-relaxed variants. Note that this
> strengthens the relaxed read accessors, since they are now ordered with
> respect to each other by way of a compiler barrier.

OK, do we want/need that compiler barrier?  And you say "strengthens" -
strengthens with respect to what if we didn't have them before?

	-hpa

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