[src/trunk]: src/sys/arch/aarch64/include daif_disable: since we read bits be...

[jmcneill <jmcneill%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/a850397f0c56
branches:  trunk
changeset: 1018891:a850397f0c56
user:      jmcneill <jmcneill%NetBSD.org@localhost>
date:      Sat Feb 20 19:27:35 2021 +0000

description:
daif_disable: since we read bits before setting them, if the current state
matches the desired state we can skip the daif write

diffstat:

 sys/arch/aarch64/include/locore.h |  12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diffs (26 lines):

diff -r 8686d720326b -r a850397f0c56 sys/arch/aarch64/include/locore.h
--- a/sys/arch/aarch64/include/locore.h Sat Feb 20 19:10:37 2021 +0000
+++ b/sys/arch/aarch64/include/locore.h Sat Feb 20 19:27:35 2021 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: locore.h,v 1.7 2021/02/07 21:15:09 jmcneill Exp $ */
+/* $NetBSD: locore.h,v 1.8 2021/02/20 19:27:35 jmcneill Exp $ */
 
 /*-
  * Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -80,10 +80,12 @@
 daif_disable(register_t psw)
 {
        register_t oldpsw = reg_daif_read();
-       if (!__builtin_constant_p(psw)) {
-               reg_daif_write(oldpsw | psw);
-       } else {
-               reg_daifset_write((psw & DAIF_MASK) >> DAIF_SETCLR_SHIFT);
+       if ((oldpsw & psw) != psw) {
+               if (!__builtin_constant_p(psw)) {
+                       reg_daif_write(oldpsw | psw);
+               } else {
+                       reg_daifset_write((psw & DAIF_MASK) >> DAIF_SETCLR_SHIFT);
+               }
        }
        return oldpsw;
 }