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2024-05-10 37f49e37ab4cb5d0bc4c60eb5c6d4dd57db767bb

 kernel/kernel/cpu_pm.c
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@@ -1,18 +1,9 @@
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+// SPDX-License-Identifier: GPL-2.0-only
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 /*
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  * Copyright (C) 2011 Google, Inc.
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  *
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  * Author:
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  *	Colin Cross <ccross@android.com>
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- *
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- * This software is licensed under the terms of the GNU General Public
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- * License version 2, as published by the Free Software Foundation, and
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- * may be copied, distributed, and modified under those terms.
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- *
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- * This program is distributed in the hope that it will be useful,
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- * but WITHOUT ANY WARRANTY; without even the implied warranty of
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- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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- * GNU General Public License for more details.
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- *
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  */
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8
 
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 #include <linux/kernel.h>
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@@ -22,20 +13,46 @@
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 #include <linux/spinlock.h>
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 #include <linux/syscore_ops.h>
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15
 
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-static ATOMIC_NOTIFIER_HEAD(cpu_pm_notifier_chain);
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+/*
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+ * atomic_notifiers use a spinlock_t, which can block under PREEMPT_RT.
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+ * Notifications for cpu_pm will be issued by the idle task itself, which can
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+ * never block, IOW it requires using a raw_spinlock_t.
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+ */
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+static struct {
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+	struct raw_notifier_head chain;
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+	raw_spinlock_t lock;
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+} cpu_pm_notifier = {
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+	.chain = RAW_NOTIFIER_INIT(cpu_pm_notifier.chain),
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+	.lock  = __RAW_SPIN_LOCK_UNLOCKED(cpu_pm_notifier.lock),
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+};
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-static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls)
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+static int cpu_pm_notify(enum cpu_pm_event event)
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 {
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 	int ret;
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 	/*
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-	 * __atomic_notifier_call_chain has a RCU read critical section, which
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-	 * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let
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-	 * RCU know this.
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+	 * This introduces a RCU read critical section, which could be
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+	 * disfunctional in cpu idle. Copy RCU_NONIDLE code to let RCU know
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+	 * this.
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 	 */
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 	rcu_irq_enter_irqson();
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-	ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL,
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-		nr_to_call, nr_calls);
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+	rcu_read_lock();
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+	ret = raw_notifier_call_chain(&cpu_pm_notifier.chain, event, NULL);
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+	rcu_read_unlock();
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+	rcu_irq_exit_irqson();
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+
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+	return notifier_to_errno(ret);
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+}
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+
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+static int cpu_pm_notify_robust(enum cpu_pm_event event_up, enum cpu_pm_event event_down)
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+{
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+	unsigned long flags;
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+	int ret;
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+
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+	rcu_irq_enter_irqson();
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+	raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
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+	ret = raw_notifier_call_chain_robust(&cpu_pm_notifier.chain, event_up, event_down, NULL);
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+	raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
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 	rcu_irq_exit_irqson();
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 	return notifier_to_errno(ret);
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@@ -48,12 +65,17 @@
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  * Add a driver to a list of drivers that are notified about
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  * CPU and CPU cluster low power entry and exit.
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  *
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- * This function may sleep, and has the same return conditions as
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- * raw_notifier_chain_register.
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+ * This function has the same return conditions as raw_notifier_chain_register.
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  */
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 int cpu_pm_register_notifier(struct notifier_block *nb)
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 {
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-	return atomic_notifier_chain_register(&cpu_pm_notifier_chain, nb);
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+	unsigned long flags;
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+	int ret;
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+
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+	raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
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+	ret = raw_notifier_chain_register(&cpu_pm_notifier.chain, nb);
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+	raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
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+	return ret;
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 }
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 EXPORT_SYMBOL_GPL(cpu_pm_register_notifier);
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@@ -63,12 +85,17 @@
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  *
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  * Remove a driver from the CPU PM notifier list.
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  *
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- * This function may sleep, and has the same return conditions as
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- * raw_notifier_chain_unregister.
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+ * This function has the same return conditions as raw_notifier_chain_unregister.
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  */
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 int cpu_pm_unregister_notifier(struct notifier_block *nb)
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 {
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-	return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb);
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+	unsigned long flags;
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+	int ret;
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+
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+	raw_spin_lock_irqsave(&cpu_pm_notifier.lock, flags);
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+	ret = raw_notifier_chain_unregister(&cpu_pm_notifier.chain, nb);
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+	raw_spin_unlock_irqrestore(&cpu_pm_notifier.lock, flags);
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+	return ret;
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 }
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 EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);
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@@ -89,18 +116,7 @@
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  */
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 int cpu_pm_enter(void)
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 {
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-	int nr_calls = 0;
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-	int ret = 0;
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-
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-	ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);
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-	if (ret)
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-		/*
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-		 * Inform listeners (nr_calls - 1) about failure of CPU PM
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-		 * PM entry who are notified earlier to prepare for it.
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-		 */
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-		cpu_pm_notify(CPU_PM_ENTER_FAILED, nr_calls - 1, NULL);
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-
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-	return ret;
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+	return cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
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 }
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 EXPORT_SYMBOL_GPL(cpu_pm_enter);
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@@ -118,7 +134,7 @@
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  */
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 int cpu_pm_exit(void)
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 {
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-	return cpu_pm_notify(CPU_PM_EXIT, -1, NULL);
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+	return cpu_pm_notify(CPU_PM_EXIT);
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 }
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 EXPORT_SYMBOL_GPL(cpu_pm_exit);
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@@ -140,18 +156,7 @@
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  */
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 int cpu_cluster_pm_enter(void)
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 {
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-	int nr_calls = 0;
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-	int ret = 0;
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-
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-	ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls);
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-	if (ret)
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-		/*
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-		 * Inform listeners (nr_calls - 1) about failure of CPU cluster
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-		 * PM entry who are notified earlier to prepare for it.
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-		 */
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-		cpu_pm_notify(CPU_CLUSTER_PM_ENTER_FAILED, nr_calls - 1, NULL);
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-
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-	return ret;
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+	return cpu_pm_notify_robust(CPU_CLUSTER_PM_ENTER, CPU_CLUSTER_PM_ENTER_FAILED);
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 }
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 EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter);
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@@ -172,7 +177,7 @@
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  */
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 int cpu_cluster_pm_exit(void)
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 {
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-	return cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL);
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+	return cpu_pm_notify(CPU_CLUSTER_PM_EXIT);
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 }
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 EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);
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