[PATCH 3/5] hwmon: (pmbus/core) Protect regulator operations with mutex

[Guenter Roeck <linux@roeck-us.net>]

The regulator operations pmbus_regulator_get_voltage(),
pmbus_regulator_set_voltage(), and pmbus_regulator_list_voltage()
access PMBus registers and shared data but were not protected by
the update_lock mutex. This could lead to race conditions.

However, adding mutex protection directly to these functions causes
a deadlock because pmbus_regulator_notify() (which calls
regulator_notifier_call_chain()) is often called with the mutex
already held (e.g., from pmbus_fault_handler()). If a regulator
callback then calls one of the now-protected voltage functions,
it will attempt to acquire the same mutex.

Rework pmbus_regulator_notify() to utilize a worker function to
send notifications outside of the mutex protection. Events are
stored as atomics in a per-page bitmask and processed by the worker.

Initialize the worker and its associated data during regulator
registration, and ensure it is cancelled on device removal using
devm_add_action_or_reset().

While at it, remove the unnecessary include of linux/of.h.

Cc: Sanman Pradhan <psanman@juniper.net>
Fixes: ddbb4db4ced1b ("hwmon: (pmbus) Add regulator support")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/pmbus/pmbus_core.c | 114 ++++++++++++++++++++++++-------
 1 file changed, 89 insertions(+), 25 deletions(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index cbc36f0ba4bf..572be3ebc03d 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -6,6 +6,7 @@
  * Copyright (c) 2012 Guenter Roeck
  */
 
+#include <linux/atomic.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/dcache.h>
@@ -21,8 +22,8 @@
 #include <linux/pmbus.h>
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>
-#include <linux/of.h>
 #include <linux/thermal.h>
+#include <linux/workqueue.h>
 #include "pmbus.h"
 
 /*
@@ -112,6 +113,11 @@ struct pmbus_data {
 
 	struct mutex update_lock;
 
+#if IS_ENABLED(CONFIG_REGULATOR)
+	atomic_t regulator_events[PMBUS_PAGES];
+	struct work_struct regulator_notify_work;
+#endif
+
 	bool has_status_word;		/* device uses STATUS_WORD register */
 	int (*read_status)(struct i2c_client *client, int page);
 
@@ -3228,12 +3234,19 @@ static int pmbus_regulator_get_voltage(struct regulator_dev *rdev)
 		.class = PSC_VOLTAGE_OUT,
 		.convert = true,
 	};
+	int ret;
 
+	mutex_lock(&data->update_lock);
 	s.data = _pmbus_read_word_data(client, s.page, 0xff, PMBUS_READ_VOUT);
-	if (s.data < 0)
-		return s.data;
+	if (s.data < 0) {
+		ret = s.data;
+		goto unlock;
+	}
 
-	return (int)pmbus_reg2data(data, &s) * 1000; /* unit is uV */
+	ret = (int)pmbus_reg2data(data, &s) * 1000; /* unit is uV */
+unlock:
+	mutex_unlock(&data->update_lock);
+	return ret;
 }
 
 static int pmbus_regulator_set_voltage(struct regulator_dev *rdev, int min_uv,
@@ -3250,16 +3263,22 @@ static int pmbus_regulator_set_voltage(struct regulator_dev *rdev, int min_uv,
 	};
 	int val = DIV_ROUND_CLOSEST(min_uv, 1000); /* convert to mV */
 	int low, high;
+	int ret;
 
 	*selector = 0;
 
+	mutex_lock(&data->update_lock);
 	low = pmbus_regulator_get_low_margin(client, s.page);
-	if (low < 0)
-		return low;
+	if (low < 0) {
+		ret = low;
+		goto unlock;
+	}
 
 	high = pmbus_regulator_get_high_margin(client, s.page);
-	if (high < 0)
-		return high;
+	if (high < 0) {
+		ret = high;
+		goto unlock;
+	}
 
 	/* Make sure we are within margins */
 	if (low > val)
@@ -3269,7 +3288,10 @@ static int pmbus_regulator_set_voltage(struct regulator_dev *rdev, int min_uv,
 
 	val = pmbus_data2reg(data, &s, val);
 
-	return _pmbus_write_word_data(client, s.page, PMBUS_VOUT_COMMAND, (u16)val);
+	ret = _pmbus_write_word_data(client, s.page, PMBUS_VOUT_COMMAND, (u16)val);
+unlock:
+	mutex_unlock(&data->update_lock);
+	return ret;
 }
 
 static int pmbus_regulator_list_voltage(struct regulator_dev *rdev,
@@ -3279,6 +3301,7 @@ static int pmbus_regulator_list_voltage(struct regulator_dev *rdev,
 	struct i2c_client *client = to_i2c_client(dev->parent);
 	struct pmbus_data *data = i2c_get_clientdata(client);
 	int val, low, high;
+	int ret;
 
 	if (data->flags & PMBUS_VOUT_PROTECTED)
 		return 0;
@@ -3291,18 +3314,29 @@ static int pmbus_regulator_list_voltage(struct regulator_dev *rdev,
 	val = DIV_ROUND_CLOSEST(rdev->desc->min_uV +
 				(rdev->desc->uV_step * selector), 1000); /* convert to mV */
 
+	mutex_lock(&data->update_lock);
+
 	low = pmbus_regulator_get_low_margin(client, rdev_get_id(rdev));
-	if (low < 0)
-		return low;
+	if (low < 0) {
+		ret = low;
+		goto unlock;
+	}
 
 	high = pmbus_regulator_get_high_margin(client, rdev_get_id(rdev));
-	if (high < 0)
-		return high;
+	if (high < 0) {
+		ret = high;
+		goto unlock;
+	}
 
-	if (val >= low && val <= high)
-		return val * 1000; /* unit is uV */
+	if (val >= low && val <= high) {
+		ret = val * 1000; /* unit is uV */
+		goto unlock;
+	}
 
-	return 0;
+	ret = 0;
+unlock:
+	mutex_unlock(&data->update_lock);
+	return ret;
 }
 
 const struct regulator_ops pmbus_regulator_ops = {
@@ -3333,12 +3367,42 @@ int pmbus_regulator_init_cb(struct regulator_dev *rdev,
 }
 EXPORT_SYMBOL_NS_GPL(pmbus_regulator_init_cb, "PMBUS");
 
+static void pmbus_regulator_notify_work_cancel(void *data)
+{
+	struct pmbus_data *pdata = data;
+
+	cancel_work_sync(&pdata->regulator_notify_work);
+}
+
+static void pmbus_regulator_notify_worker(struct work_struct *work)
+{
+	struct pmbus_data *data =
+		container_of(work, struct pmbus_data, regulator_notify_work);
+	int i, j;
+
+	for (i = 0; i < data->info->pages; i++) {
+		int event;
+
+		event = atomic_xchg(&data->regulator_events[i], 0);
+		if (!event)
+			continue;
+
+		for (j = 0; j < data->info->num_regulators; j++) {
+			if (i == rdev_get_id(data->rdevs[j])) {
+				regulator_notifier_call_chain(data->rdevs[j],
+							      event, NULL);
+				break;
+			}
+		}
+	}
+}
+
 static int pmbus_regulator_register(struct pmbus_data *data)
 {
 	struct device *dev = data->dev;
 	const struct pmbus_driver_info *info = data->info;
 	const struct pmbus_platform_data *pdata = dev_get_platdata(dev);
-	int i;
+	int i, ret;
 
 	data->rdevs = devm_kzalloc(dev, sizeof(struct regulator_dev *) * info->num_regulators,
 				   GFP_KERNEL);
@@ -3362,19 +3426,19 @@ static int pmbus_regulator_register(struct pmbus_data *data)
 					     info->reg_desc[i].name);
 	}
 
+	INIT_WORK(&data->regulator_notify_work, pmbus_regulator_notify_worker);
+
+	ret = devm_add_action_or_reset(dev, pmbus_regulator_notify_work_cancel, data);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
 static void pmbus_regulator_notify(struct pmbus_data *data, int page, int event)
 {
-	int j;
-
-	for (j = 0; j < data->info->num_regulators; j++) {
-		if (page == rdev_get_id(data->rdevs[j])) {
-			regulator_notifier_call_chain(data->rdevs[j], event, NULL);
-			break;
-		}
-	}
+	atomic_or(event, &data->regulator_events[page]);
+	schedule_work(&data->regulator_notify_work);
 }
 #else
 static int pmbus_regulator_register(struct pmbus_data *data)
-- 
2.45.2