[PATCH v6 3/9] rtc: abx80x: add mutex protection for register writes

[Antoni Pokusinski]

The ABX80X RTC driver performs multi-step register operations such as
NVMEM transfers or register writes preceded by a configuration key
write. Add a mutex to serialize all the register writes to protect
these sequences against race conditions.

Signed-off-by: Antoni Pokusinski <apokusinski01@xxxxxxxxx>
---
 drivers/rtc/rtc-abx80x.c | 45 +++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/rtc/rtc-abx80x.c b/drivers/rtc/rtc-abx80x.c
index e4fd7b5d4b11..44de234efecf 100644
--- a/drivers/rtc/rtc-abx80x.c
+++ b/drivers/rtc/rtc-abx80x.c
@@ -15,6 +15,7 @@
 #include <linux/i2c.h>
 #include <linux/kstrtox.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/rtc.h>
 #include <linux/watchdog.h>
@@ -127,6 +128,7 @@ struct abx80x_priv {
 	struct rtc_device *rtc;
 	struct i2c_client *client;
 	struct watchdog_device wdog;
+	struct mutex lock;
 };
 
 static int abx80x_write_config_key(struct i2c_client *client, u8 key)
@@ -219,6 +221,7 @@ static int abx80x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 static int abx80x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	unsigned char buf[8];
 	int err, flags;
 
@@ -234,6 +237,8 @@ static int abx80x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	buf[ABX8XX_REG_YR] = bin2bcd(tm->tm_year - 100);
 	buf[ABX8XX_REG_WD] = tm->tm_wday;
 
+	guard(mutex)(&priv->lock);
+
 	err = i2c_smbus_write_i2c_block_data(client, ABX8XX_REG_HTH,
 					     sizeof(buf), buf);
 	if (err < 0) {
@@ -263,6 +268,8 @@ static irqreturn_t abx80x_handle_irq(int irq, void *dev_id)
 	struct rtc_device *rtc = priv->rtc;
 	int status;
 
+	guard(mutex)(&priv->lock);
+
 	status = i2c_smbus_read_byte_data(client, ABX8XX_REG_STATUS);
 	if (status < 0)
 		return IRQ_NONE;
@@ -319,6 +326,7 @@ static int abx80x_read_alarm(struct device *dev, struct rtc_wkalrm *t)
 static int abx80x_set_alarm(struct device *dev, struct rtc_wkalrm *t)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	u8 alarm[6];
 	int err;
 
@@ -332,6 +340,8 @@ static int abx80x_set_alarm(struct device *dev, struct rtc_wkalrm *t)
 	alarm[4] = bin2bcd(t->time.tm_mday);
 	alarm[5] = bin2bcd(t->time.tm_mon + 1);
 
+	guard(mutex)(&priv->lock);
+
 	err = i2c_smbus_write_i2c_block_data(client, ABX8XX_REG_AHTH,
 					     sizeof(alarm), alarm);
 	if (err < 0) {
@@ -354,6 +364,7 @@ static int abx80x_rtc_set_autocalibration(struct device *dev,
 					  int autocalibration)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	int retval, flags = 0;
 
 	if ((autocalibration != 0) && (autocalibration != 1024) &&
@@ -362,6 +373,8 @@ static int abx80x_rtc_set_autocalibration(struct device *dev,
 		return -EINVAL;
 	}
 
+	guard(mutex)(&priv->lock);
+
 	flags = i2c_smbus_read_byte_data(client, ABX8XX_REG_OSC);
 	if (flags < 0)
 		return flags;
@@ -445,6 +458,7 @@ static ssize_t oscillator_store(struct device *dev,
 				const char *buf, size_t count)
 {
 	struct i2c_client *client = to_i2c_client(dev->parent);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	int retval, flags, rc_mode = 0;
 
 	if (strncmp(buf, "rc", 2) == 0) {
@@ -456,6 +470,8 @@ static ssize_t oscillator_store(struct device *dev,
 		return -EINVAL;
 	}
 
+	guard(mutex)(&priv->lock);
+
 	flags =  i2c_smbus_read_byte_data(client, ABX8XX_REG_OSC);
 	if (flags < 0)
 		return flags;
@@ -513,8 +529,11 @@ static const struct attribute_group rtc_calib_attr_group = {
 static int abx80x_alarm_irq_enable(struct device *dev, unsigned int enabled)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	int err;
 
+	guard(mutex)(&priv->lock);
+
 	if (enabled)
 		err = i2c_smbus_write_byte_data(client, ABX8XX_REG_IRQ,
 						(ABX8XX_IRQ_IM_1_4 |
@@ -528,6 +547,7 @@ static int abx80x_alarm_irq_enable(struct device *dev, unsigned int enabled)
 static int abx80x_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
 {
 	struct i2c_client *client = to_i2c_client(dev);
+	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	int status, tmp;
 
 	switch (cmd) {
@@ -541,16 +561,18 @@ static int abx80x_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
 		return put_user(tmp, (unsigned int __user *)arg);
 
 	case RTC_VL_CLR:
-		status = i2c_smbus_read_byte_data(client, ABX8XX_REG_STATUS);
-		if (status < 0)
-			return status;
+		scoped_guard(mutex, &priv->lock) {
+			status = i2c_smbus_read_byte_data(client, ABX8XX_REG_STATUS);
+			if (status < 0)
+				return status;
 
-		status &= ~ABX8XX_STATUS_BLF;
+			status &= ~ABX8XX_STATUS_BLF;
 
-		tmp = i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS,
-						status);
-		if (tmp < 0)
-			return tmp;
+			tmp = i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS,
+							status);
+			if (tmp < 0)
+				return tmp;
+		}
 
 		return 0;
 
@@ -619,6 +641,8 @@ static int __abx80x_wdog_set_timeout(struct watchdog_device *wdog,
 	struct abx80x_priv *priv = watchdog_get_drvdata(wdog);
 	u8 val = ABX8XX_WDT_WDS | timeout_bits(timeout);
 
+	guard(mutex)(&priv->lock);
+
 	/*
 	 * Writing any timeout to the WDT register resets the watchdog timer.
 	 * Writing 0 disables it.
@@ -703,6 +727,8 @@ static int abx80x_nvmem_xfer(struct abx80x_priv *priv, unsigned int offset,
 		len = min(lower + bytes, (size_t)ABX8XX_SRAM_WIN_SIZE) - lower;
 		len = min_t(u8, len, I2C_SMBUS_BLOCK_MAX);
 
+		guard(mutex)(&priv->lock);
+
 		ret = i2c_smbus_write_byte_data(priv->client, ABX8XX_REG_EXTRAM,
 						extram);
 		if (ret)
@@ -910,6 +936,9 @@ static int abx80x_probe(struct i2c_client *client)
 
 	priv->rtc->ops = &abx80x_rtc_ops;
 	priv->client = client;
+	err = devm_mutex_init(&client->dev, &priv->lock);
+	if (err)
+		return err;
 
 	i2c_set_clientdata(client, priv);
 
-- 
2.55.0