[RFC PATCH 1/3] pmdomain: core: Allow a non-CPU device in a CPU PM domain to do power on

[Ulf Hansson <ulf.hansson@oss.qualcomm.com>]

From: Ulf Hansson <ulfh@kernel.org>

A driver for a non-CPU device that is attached to a CPU PM domain (the
genpd has the GENPD_FLAG_CPU_DOMAIN configuration set), is currently not
able to power on the PM domain. More precisely, to power on a CPU PM domain
one of its corresponding CPUs needs to be woken up if they are idle.

The current support for a non-CPU device is that its driver can only
prevent an already powered on CPU PM domain from being powered off. This
leads to problems for a driver while probing its device or when it needs to
call pm_runtime_get_sync() to turn on the power for it. From the driver
point of view it looks like it all works fine, but when accessing the
device it may end up with various errors as the device may not be fully
powered on.

To fix the behavior for these types of devices, let's adjust the behaviour
in genpd_power_on() to wake up an idle CPU that belongs to it, in cases
when it's needed.

Link: https://lore.kernel.org/all/CAPx+jO-sCierYj8jnoKQHckJG16dOBxnNrsZVYO=38R2cLV8nw@mail.gmail.com/
Signed-off-by: Ulf Hansson <ulfh@kernel.org>
---
 drivers/pmdomain/core.c | 80 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 75 insertions(+), 5 deletions(-)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index 842c4169e290..7345c06f1d55 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -10,6 +10,7 @@
 #include <linux/idr.h>
 #include <linux/kernel.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/platform_device.h>
 #include <linux/pm_opp.h>
 #include <linux/pm_runtime.h>
@@ -19,11 +20,14 @@
 #include <linux/slab.h>
 #include <linux/err.h>
 #include <linux/sched.h>
+#include <linux/smp.h>
 #include <linux/suspend.h>
 #include <linux/export.h>
 #include <linux/cpu.h>
 #include <linux/debugfs.h>
 
+#include <trace/events/ipi.h>
+
 /* Provides a unique ID for each genpd device */
 static DEFINE_IDA(genpd_ida);
 
@@ -32,7 +36,9 @@ static const struct bus_type genpd_provider_bus_type = {
 	.name		= "genpd_provider",
 };
 
-#define GENPD_RETRY_MAX_MS	250		/* Approximate */
+#define GENPD_RETRY_MAX_MS		250		/* Approximate */
+#define GENPD_CPU_ON_POLL_PERIOD_US	100		/* 100us */
+#define GENPD_CPU_ON_TIMEOUT_US		5000000		/* 5s */
 
 #define GENPD_DEV_CALLBACK(genpd, type, callback, dev)		\
 ({								\
@@ -1027,15 +1033,75 @@ static void genpd_power_off(struct generic_pm_domain *genpd, bool one_dev_on,
 	}
 }
 
+static bool genpd_check_status_on(struct generic_pm_domain *genpd)
+{
+	bool is_on;
+
+	genpd_lock(genpd);
+	is_on = genpd_status_on(genpd);
+	genpd_unlock(genpd);
+
+	return is_on;
+}
+
+static int genpd_wakeup_cpu(struct generic_pm_domain *genpd)
+{
+	unsigned int cpu;
+	bool is_on;
+	int ret;
+
+	/* Find the first online CPU in the genpd's cpumask. */
+	cpu = cpumask_first_and(genpd->cpus, cpu_online_mask);
+	if (cpu >= nr_cpu_ids)
+		return -EAGAIN;
+
+	genpd_unlock(genpd);
+
+	/* Send a IPI to wakeup the selected CPU. */
+	smp_send_reschedule(cpu);
+
+	/* Poll to wait for it to complete the power on sequence. */
+	ret = readx_poll_timeout(genpd_check_status_on, genpd, is_on, is_on,
+				 GENPD_CPU_ON_POLL_PERIOD_US,
+				 GENPD_CPU_ON_TIMEOUT_US);
+
+	genpd_lock(genpd);
+
+	/* Re-check the status as we have released the lock in between. */
+	if (ret || !genpd_status_on(genpd))
+		return -EAGAIN;
+
+	return 0;
+}
+
+static bool genpd_need_alive_cpu(struct generic_pm_domain *genpd,
+				 struct device *dev)
+{
+	if (!genpd_is_cpu_domain(genpd))
+		return false;
+
+	/* This is not for CPU devices as those are managed differently. */
+	if (to_gpd_data(dev->power.subsys_data->domain_data)->cpu >= 0)
+		return false;
+
+	/*
+	 * If the current CPU doesn't belong to the genpd's cpumask, we need to
+	 * wake up one of those idle CPUs to power on the CPU domain correctly.
+	 */
+	return !cpumask_test_cpu(smp_processor_id(), genpd->cpus);
+}
+
 /**
  * genpd_power_on - Restore power to a given PM domain and its parents.
  * @genpd: PM domain to power up.
+ * @dev: The device that needs the PM domain to power on.
  * @depth: nesting count for lockdep.
  *
  * Restore power to @genpd and all of its parents so that it is possible to
  * resume a device belonging to it.
  */
-static int genpd_power_on(struct generic_pm_domain *genpd, unsigned int depth)
+static int genpd_power_on(struct generic_pm_domain *genpd, struct device *dev,
+			  unsigned int depth)
 {
 	struct gpd_link *link;
 	int ret = 0;
@@ -1043,6 +1109,10 @@ static int genpd_power_on(struct generic_pm_domain *genpd, unsigned int depth)
 	if (genpd_status_on(genpd))
 		return 0;
 
+	/* Special case for a device attached to a CPU domain. */
+	if (genpd_need_alive_cpu(genpd, dev))
+		return genpd_wakeup_cpu(genpd);
+
 	/* Reflect over the entered idle-states residency for debugfs. */
 	genpd_reflect_residency(genpd);
 
@@ -1057,7 +1127,7 @@ static int genpd_power_on(struct generic_pm_domain *genpd, unsigned int depth)
 		genpd_sd_counter_inc(parent);
 
 		genpd_lock_nested(parent, depth + 1);
-		ret = genpd_power_on(parent, depth + 1);
+		ret = genpd_power_on(parent, dev, depth + 1);
 		genpd_unlock(parent);
 
 		if (ret) {
@@ -1307,7 +1377,7 @@ static int genpd_runtime_resume(struct device *dev)
 
 	genpd_lock(genpd);
 	genpd_restore_performance_state(dev, gpd_data->rpm_pstate);
-	ret = genpd_power_on(genpd, 0);
+	ret = genpd_power_on(genpd, dev, 0);
 	genpd_unlock(genpd);
 
 	if (ret)
@@ -3410,7 +3480,7 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
 
 	if (power_on) {
 		genpd_lock(pd);
-		ret = genpd_power_on(pd, 0);
+		ret = genpd_power_on(pd, dev, 0);
 		genpd_unlock(pd);
 	}
 
-- 
2.43.0