[PATCH RFC LKMM 5/7] docs/memory-barriers.txt: Enforce heavy ordering for port I/O accesses

[Paul E. McKenney]

From: Will Deacon <will.deacon@xxxxxxx>

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@xxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: <linux-arch@xxxxxxxxxxxxxxx>
Cc: <linux-doc@xxxxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
 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 1c22b21ae922..a70104e2a087 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():
 
-- 
2.17.1