[PATCH v4 6/6] powerpc: implement smp_cond_load_relaxed

Nicholas Piggin
Fri, 24 Jul 2020 13:14:23 -0000

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

Signed-off-by: Nicholas Piggin <npiggin at gmail.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