hwmon: (pmbus/adm1266) serialize GPIO PMBus accesses with pmbus_lock

adm1266_gpio_get(), adm1266_gpio_get_multiple(), and
adm1266_gpio_dbg_show() all issue PMBus reads against the device but
none of them take pmbus_lock.  The pmbus_core framework holds
pmbus_lock around its own multi-transaction sequences (notably the
"set PAGE, then read paged register" pattern used by hwmon
attributes), so an unlocked GPIO accessor can land between a PAGE
write and the subsequent paged read in another thread and corrupt
either side's view of the device state machine.

Take pmbus_lock at the top of each of the three accessors via the
scope-based guard().  The lock is uncontended in the common case and
adds only a single mutex round-trip per call.

Fixes: d98dfad ("hwmon: (pmbus/adm1266) Add support for GPIOs")
Cc: stable@vger.kernel.org
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260518-adm1266-gpio-fixes-v3-6-e425e4f88139@nexthop.ai
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: abdurrahman-nexthop

drivers/hwmon/pmbus/adm1266.c

@@ -173,6 +173,8 @@ static int adm1266_gpio_get(struct gpio_chip *chip, unsigned int offset)
 	else
 		pmbus_cmd = ADM1266_PDIO_STATUS;
 
+	guard(pmbus_lock)(data->client);
+
 	ret = i2c_smbus_read_block_data(data->client, pmbus_cmd, read_buf);
 	if (ret < 0)
 		return ret;
@@ -195,6 +197,8 @@ static int adm1266_gpio_get_multiple(struct gpio_chip *chip, unsigned long *mask
 	unsigned int gpio_nr;
 	int ret;
 
+	guard(pmbus_lock)(data->client);
+
 	ret = i2c_smbus_read_block_data(data->client, ADM1266_GPIO_STATUS, read_buf);
 	if (ret < 0)
 		return ret;
@@ -236,6 +240,8 @@ static void adm1266_gpio_dbg_show(struct seq_file *s, struct gpio_chip *chip)
 	int ret;
 	int i;
 
+	guard(pmbus_lock)(data->client);
+
 	for (i = 0; i < ADM1266_GPIO_NR; i++) {
 		write_cmd = adm1266_gpio_mapping[i][1];
 		ret = adm1266_pmbus_block_xfer(data, ADM1266_GPIO_CONFIG, 1, &write_cmd, read_buf);