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Cc:     Andrzej Hajda <andrzej.hajda@intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>
Subject: [PATCH v5 2/7] linux/include: add non-atomic version of xchg
Date:   Wed, 18 Jan 2023 16:44:45 +0100
Message-Id: <20230118154450.73842-2-andrzej.hajda@intel.com>
In-Reply-To: <20230118154450.73842-1-andrzej.hajda@intel.com>
References: <20230118153529.57695-1-andrzej.hajda@intel.com>
 <20230118154450.73842-1-andrzej.hajda@intel.com>
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The pattern of setting variable with new value and returning old
one is very common in kernel. Usually atomicity of the operation
is not required, so xchg seems to be suboptimal and confusing in
such cases.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 include/linux/non-atomic/xchg.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 include/linux/non-atomic/xchg.h

diff --git a/include/linux/non-atomic/xchg.h b/include/linux/non-atomic/xchg.h
new file mode 100644
index 00000000000000..f7fa5dd746f37d
--- /dev/null
+++ b/include/linux/non-atomic/xchg.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_NON_ATOMIC_XCHG_H
+#define _LINUX_NON_ATOMIC_XCHG_H
+
+/**
+ * __xchg - set variable pointed by @ptr to @val, return old value
+ * @ptr: pointer to affected variable
+ * @val: value to be written
+ *
+ * This is non-atomic variant of xchg.
+ */
+#define __xchg(ptr, val) ({		\
+	__auto_type __ptr = ptr;	\
+	__auto_type __t = *__ptr;	\
+	*__ptr = (val);			\
+	__t;				\
+})
+
+#endif
-- 
2.34.1