Message-ID: <20251016151929.75863-2-ulf.hansson@linaro.org>
Date: Thu, 16 Oct 2025 17:19:21 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	linux-pm@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kevin Hilman <khilman@...libre.com>,
	Pavel Machek <pavel@...nel.org>,
	Len Brown <len.brown@...el.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Maulik Shah <quic_mkshah@...cinc.com>,
	Prasad Sodagudi <psodagud@...cinc.com>,
	Dhruva Gole <d-gole@...com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/4] PM: QoS: Introduce a CPU system-wakeup QoS limit

Some platforms supports multiple low-power states for CPUs that can be used
when entering system-wide suspend. Currently we are always selecting the
deepest possible state for the CPUs, which can break the system-wakeup
latency constraint that may be required for some use-cases.

Let's take the first step towards addressing this problem, by introducing
an interface for user-space, that allows us to specify the CPU
system-wakeup QoS limit. Subsequent changes will start taking into account
the new QoS limit.

Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---

Changes in v2:
	- Renamings to reflect the QoS are limited to CPUs.
	- Move code inside "CONFIG_CPU_IDLE".

---
 include/linux/pm_qos.h |   5 ++
 kernel/power/qos.c     | 102 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+)

diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
index 4a69d4af3ff8..bf7524d38933 100644
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -149,6 +149,7 @@ bool cpu_latency_qos_request_active(struct pm_qos_request *req);
 void cpu_latency_qos_add_request(struct pm_qos_request *req, s32 value);
 void cpu_latency_qos_update_request(struct pm_qos_request *req, s32 new_value);
 void cpu_latency_qos_remove_request(struct pm_qos_request *req);
+s32 cpu_wakeup_latency_qos_limit(void);
 #else
 static inline s32 cpu_latency_qos_limit(void) { return INT_MAX; }
 static inline bool cpu_latency_qos_request_active(struct pm_qos_request *req)
@@ -160,6 +161,10 @@ static inline void cpu_latency_qos_add_request(struct pm_qos_request *req,
 static inline void cpu_latency_qos_update_request(struct pm_qos_request *req,
 						  s32 new_value) {}
 static inline void cpu_latency_qos_remove_request(struct pm_qos_request *req) {}
+static inline s32 cpu_wakeup_latency_qos_limit(void)
+{
+	return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+}
 #endif
 
 #ifdef CONFIG_PM
diff --git a/kernel/power/qos.c b/kernel/power/qos.c
index 4244b069442e..8c024d7dc43e 100644
--- a/kernel/power/qos.c
+++ b/kernel/power/qos.c
@@ -415,6 +415,103 @@ static struct miscdevice cpu_latency_qos_miscdev = {
 	.fops = &cpu_latency_qos_fops,
 };
 
+/* The CPU system wakeup latency QoS. */
+static struct pm_qos_constraints cpu_wakeup_latency_constraints = {
+	.list = PLIST_HEAD_INIT(cpu_wakeup_latency_constraints.list),
+	.target_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT,
+	.default_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT,
+	.no_constraint_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT,
+	.type = PM_QOS_MIN,
+};
+
+/**
+ * cpu_wakeup_latency_qos_limit - Current CPU system wakeup latency QoS limit.
+ *
+ * Returns the current CPU system wakeup latency QoS limit that may have been
+ * requested by user-space.
+ */
+s32 cpu_wakeup_latency_qos_limit(void)
+{
+	return pm_qos_read_value(&cpu_wakeup_latency_constraints);
+}
+
+static int cpu_wakeup_latency_qos_open(struct inode *inode, struct file *filp)
+{
+	struct pm_qos_request *req;
+
+	req = kzalloc(sizeof(*req), GFP_KERNEL);
+	if (!req)
+		return -ENOMEM;
+
+	req->qos = &cpu_wakeup_latency_constraints;
+	pm_qos_update_target(req->qos, &req->node, PM_QOS_ADD_REQ,
+			     PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
+	filp->private_data = req;
+
+	return 0;
+}
+
+static int cpu_wakeup_latency_qos_release(struct inode *inode,
+					  struct file *filp)
+{
+	struct pm_qos_request *req = filp->private_data;
+
+	filp->private_data = NULL;
+	pm_qos_update_target(req->qos, &req->node, PM_QOS_REMOVE_REQ,
+			     PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
+	kfree(req);
+
+	return 0;
+}
+
+static ssize_t cpu_wakeup_latency_qos_read(struct file *filp, char __user *buf,
+					   size_t count, loff_t *f_pos)
+{
+	s32 value = pm_qos_read_value(&cpu_wakeup_latency_constraints);
+
+	return simple_read_from_buffer(buf, count, f_pos, &value, sizeof(s32));
+}
+
+static ssize_t cpu_wakeup_latency_qos_write(struct file *filp,
+					    const char __user *buf,
+					    size_t count, loff_t *f_pos)
+{
+	struct pm_qos_request *req = filp->private_data;
+	s32 value;
+
+	if (count == sizeof(s32)) {
+		if (copy_from_user(&value, buf, sizeof(s32)))
+			return -EFAULT;
+	} else {
+		int ret;
+
+		ret = kstrtos32_from_user(buf, count, 16, &value);
+		if (ret)
+			return ret;
+	}
+
+	if (value < 0)
+		return -EINVAL;
+
+	pm_qos_update_target(req->qos, &req->node, PM_QOS_UPDATE_REQ, value);
+
+	return count;
+}
+
+static const struct file_operations cpu_wakeup_latency_qos_fops = {
+	.open = cpu_wakeup_latency_qos_open,
+	.release = cpu_wakeup_latency_qos_release,
+	.read = cpu_wakeup_latency_qos_read,
+	.write = cpu_wakeup_latency_qos_write,
+	.llseek = noop_llseek,
+};
+
+static struct miscdevice cpu_wakeup_latency_qos_miscdev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "cpu_wakeup_latency",
+	.fops = &cpu_wakeup_latency_qos_fops,
+};
+
 static int __init cpu_latency_qos_init(void)
 {
 	int ret;
@@ -424,6 +521,11 @@ static int __init cpu_latency_qos_init(void)
 		pr_err("%s: %s setup failed\n", __func__,
 		       cpu_latency_qos_miscdev.name);
 
+	ret = misc_register(&cpu_wakeup_latency_qos_miscdev);
+	if (ret < 0)
+		pr_err("%s: %s setup failed\n", __func__,
+		       cpu_wakeup_latency_qos_miscdev.name);
+
 	return ret;
 }
 late_initcall(cpu_latency_qos_init);
-- 
2.43.0

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