[PATCH] docs/memory-barriers.txt: Enforce heavy ordering for port I/O accesses

From: Will Deacon <will.deacon@arm.com>
To: corbet@lwn.net
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	Will Deacon <will.deacon@arm.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Arnd Bergmann <arnd@arndb.de>,
	David Laight <David.Laight@ACULAB.COM>,
	Alan Stern <stern@rowland.harvard.edu>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH] docs/memory-barriers.txt: Enforce heavy ordering for port I/O accesses
Date: Mon, 26 Nov 2018 16:52:14 +0000	[thread overview]
Message-ID: <1543251134-29867-1-git-send-email-will.deacon@arm.com> (raw)

David Laight explains:

  | A long time ago there was a document from Intel that said that
  | inb/outb weren't necessarily synchronised wrt memory accesses.
  | (Might be P-pro era). However no processors actually behaved that
  | way and more recent docs say that inb/outb are fully ordered.

This also reflects the situation on other architectures, the the port
accessor macros tend to be implemented in terms of readX/writeX.

Update Documentation/memory-barriers.txt to reflect reality.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---

Just remembered I had this patch kicking around in my tree...

 Documentation/memory-barriers.txt | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index c1d913944ad8..0c34c5dac138 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -2619,10 +2619,8 @@ functions:
      intermediary bridges (such as the PCI host bridge) may not fully honour
      that.
 
-     They are guaranteed to be fully ordered with respect to each other.
-
-     They are not guaranteed to be fully ordered with respect to other types of
-     memory and I/O operation.
+     They are guaranteed to be fully ordered with respect to each other and
+     also with respect to other types of memory and I/O operation.
 
  (*) readX(), writeX():
 
-- 
2.1.4

