linux-kernel - [PATCH v4 6/6] powerpc: implement smp_cond_load

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Message-Id: <20200724131423.1362108-7-npiggin@gmail.com>
Date:   Fri, 24 Jul 2020 23:14:23 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     Nicholas Piggin <npiggin@...il.com>, Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Anton Blanchard <anton@...abs.org>,
        Michal Suchánek <msuchanek@...e.de>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm-ppc@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: [PATCH v4 6/6] powerpc: implement smp_cond_load_relaxed

This implements smp_cond_load_relaed with the slowpath busy loop using the
preferred SMT priority pattern.

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
 arch/powerpc/include/asm/barrier.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index 123adcefd40f..9b4671d38674 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -76,6 +76,20 @@ do {									\
 	___p1;								\
 })
 
+#define smp_cond_load_relaxed(ptr, cond_expr) ({		\
+	typeof(ptr) __PTR = (ptr);				\
+	__unqual_scalar_typeof(*ptr) VAL;			\
+	VAL = READ_ONCE(*__PTR);				\
+	if (unlikely(!(cond_expr))) {				\
+		spin_begin();					\
+		do {						\
+			VAL = READ_ONCE(*__PTR);		\
+		} while (!(cond_expr));				\
+		spin_end();					\
+	}							\
+	(typeof(*ptr))VAL;					\
+})
+
 #ifdef CONFIG_PPC_BOOK3S_64
 #define NOSPEC_BARRIER_SLOT   nop
 #elif defined(CONFIG_PPC_FSL_BOOK3E)
-- 
2.23.0