linux-kernel - [PATCH locking 2/4] documentation: State purpose of memory-barriers.txt

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Message-Id: <1461691328-5429-2-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 26 Apr 2016 10:22:06 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, corbet@....net, peterz@...radead.org,
	linux-doc@...r.kernel.org, dhowells@...hat.com,
	will.deacon@....com, dave@...olabs.net,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH locking 2/4] documentation: State purpose of memory-barriers.txt

From: David Howells <dhowells@...hat.com>

There has been some confusion about the purpose of memory-barriers.txt,
so this commit adds a statement of purpose.

Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 Documentation/memory-barriers.txt | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index fb2dd35a823a..8b11e54238bf 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -19,6 +19,22 @@ in case of any doubt (and there are many) please ask.
 To repeat, this document is not a specification of what Linux expects from
 hardware.
 
+The purpose of this document is twofold:
+
+ (1) to specify the minimum functionality that one can rely on for any
+     particular barrier, and
+
+ (2) to provide a guide as to how to use the barriers that are available.
+
+Note that an architecture can provide more than the minimum requirement
+for any particular barrier, but if the architecure provides less than
+that, that architecture is incorrect.
+
+Note also that it is possible that a barrier may be a no-op for an
+architecture because the way that arch works renders an explicit barrier
+unnecessary in that case.
+
+
 ========
 CONTENTS
 ========
-- 
2.5.2