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From: John David Anglin <dave.anglin@bell.net>
To: linux-parisc <linux-parisc@vger.kernel.org>
Cc: Helge Deller <deller@gmx.de>,
	James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: [PATCH] parisc: Remove ldcw barriers from LWS routines in syscall.S
Date: Tue, 21 Jul 2020 09:10:59 -0400
Message-ID: <4e679f6d-e7e7-fe38-5d79-8de3a022a510@bell.net> (raw)

The LDCW barriers in the light-weight system (LWS) calls in syscall.S can be removed.  Ordered stores
can be used to provide the necessary release semantics.  This saves an instruction that is relatively
expensive.

Signed-off-by: Dave Anglin <dave.anglin@bell.net>
---

diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index f05c9d5b6b9e..069c7c93d16b 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -640,11 +640,7 @@ cas_action:
 	sub,<>	%r28, %r25, %r0
 2:	stw	%r24, 0(%r26)
 	/* Free lock */
-#ifdef CONFIG_SMP
-98:	LDCW	0(%sr2,%r20), %r1			/* Barrier */
-99:	ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
-#endif
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)			/* Ordered store */
 #if ENABLE_LWS_DEBUG
 	/* Clear thread register indicator */
 	stw	%r0, 4(%sr2,%r20)
@@ -658,11 +654,7 @@ cas_action:
 3:		
 	/* Error occurred on load or store */
 	/* Free lock */
-#ifdef CONFIG_SMP
-98:	LDCW	0(%sr2,%r20), %r1			/* Barrier */
-99:	ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
-#endif
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)			/* Ordered store */
 #if ENABLE_LWS_DEBUG
 	stw	%r0, 4(%sr2,%r20)
 #endif
@@ -863,11 +855,7 @@ cas2_action:

 cas2_end:
 	/* Free lock */
-#ifdef CONFIG_SMP
-98:	LDCW	0(%sr2,%r20), %r1			/* Barrier */
-99:	ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
-#endif
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)			/* Ordered store */
 	/* Enable interrupts */
 	ssm	PSW_SM_I, %r0
 	/* Return to userspace, set no error */
@@ -876,12 +864,7 @@ cas2_end:

 22:
 	/* Error occurred on load or store */
-	/* Free lock */
-#ifdef CONFIG_SMP
-98:	LDCW	0(%sr2,%r20), %r1			/* Barrier */
-99:	ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
-#endif
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)			/* Ordered store */
 	ssm	PSW_SM_I, %r0
 	ldo	1(%r0),%r28
 	b	lws_exit

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