From 74a942e6738ba7b6549842d760110c95681a0e1c Mon Sep 17 00:00:00 2001
From: Carlo Caione <ccaione@baylibre.com>
Date: Mon, 1 May 2023 14:33:31 +0200
Subject: [PATCH] barriers: Introduce barrier operations

Introduce a new API for barrier operations starting with a general
skeleton and the implementation for barrier_data_memory_fence_full().

Select a built-in or an arch-based implementation according to new
Kconfig symbols CONFIG_BARRIER_OPERATIONS_BUILTIN and
CONFIG_BARRIER_OPERATIONS_ARCH.

The built-in implementation falls back on the compiler built-in
function using __ATOMIC_SEQ_CST as it is done for the atomic APIs
already.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
---
 include/zephyr/sys/barrier.h         | 47 ++++++++++++++++++++++++++++
 include/zephyr/sys/barrier_builtin.h | 29 +++++++++++++++++
 kernel/Kconfig                       | 15 +++++++++
 3 files changed, 91 insertions(+)
 create mode 100644 include/zephyr/sys/barrier.h
 create mode 100644 include/zephyr/sys/barrier_builtin.h

diff --git a/include/zephyr/sys/barrier.h b/include/zephyr/sys/barrier.h
new file mode 100644
index 00000000000..6acc0476ec1
--- /dev/null
+++ b/include/zephyr/sys/barrier.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2023 Carlo Caione <ccaione@baylibre.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_SYS_BARRIER_H_
+#define ZEPHYR_INCLUDE_SYS_BARRIER_H_
+
+#include <zephyr/toolchain.h>
+
+#if defined(CONFIG_BARRIER_OPERATIONS_ARCH)
+/* Empty */
+#elif defined(CONFIG_BARRIER_OPERATIONS_BUILTIN)
+#include <zephyr/sys/barrier_builtin.h>
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @addtogroup barrier_apis Barrier Services APIs
+ * @ingroup kernel_apis
+ * @{
+ */
+
+/**
+ * @brief Full/sequentially-consistent data memory barrier.
+ *
+ * This routine acts as a synchronization fence between threads and prevents
+ * re-ordering of data accesses instructions across the barrier instruction.
+ */
+static ALWAYS_INLINE void barrier_dmem_fence_full(void)
+{
+#if defined(CONFIG_BARRIER_OPERATIONS_ARCH) || defined(CONFIG_BARRIER_OPERATIONS_BUILTIN)
+	z_barrier_dmem_fence_full();
+#endif
+}
+
+/** @} */
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* ZEPHYR_INCLUDE_SYS_ATOMIC_H_ */
diff --git a/include/zephyr/sys/barrier_builtin.h b/include/zephyr/sys/barrier_builtin.h
new file mode 100644
index 00000000000..98bec6eaa36
--- /dev/null
+++ b/include/zephyr/sys/barrier_builtin.h
@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2023 Carlo Caione <ccaione@baylibre.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_SYS_BARRIER_BUILTIN_H_
+#define ZEPHYR_INCLUDE_SYS_BARRIER_BUILTIN_H_
+
+#ifndef ZEPHYR_INCLUDE_SYS_BARRIER_H_
+#error Please include <zephyr/sys/barrier.h>
+#endif
+
+#include <zephyr/toolchain.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static ALWAYS_INLINE void z_barrier_dmem_fence_full(void)
+{
+	__atomic_thread_fence(__ATOMIC_SEQ_CST);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_SYS_BARRIER_BUILTIN_H_ */
diff --git a/kernel/Kconfig b/kernel/Kconfig
index 4dceaaf662e..6dbca69694f 100644
--- a/kernel/Kconfig
+++ b/kernel/Kconfig
@@ -452,6 +452,21 @@ config SYSTEM_WORKQUEUE_NO_YIELD
 
 endmenu
 
+menu "Barrier Operations"
+config BARRIER_OPERATIONS_BUILTIN
+	bool
+	help
+	  Use the compiler builtin functions for barrier operations. This is
+	  the preferred method. However, support for all arches in GCC is
+	  incomplete.
+
+config BARRIER_OPERATIONS_ARCH
+	bool
+	help
+	  Use when there isn't support for compiler built-ins, but you have
+	  written optimized assembly code under arch/ which implements these.
+endmenu
+
 menu "Atomic Operations"
 config ATOMIC_OPERATIONS_BUILTIN
 	bool