[PATCH 06/11] hwmon: (nct6683) Fix incorrect struct cast in show_pwm() and store_pwm()

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

On big-endian architectures, reading or writing the pwm[1-8] sysfs
attributes in the nct6683 hardware monitoring driver always redirects to
channel 0 due to an incorrect struct downcast in show_pwm() and
store_pwm().
The driver defines the PWM sysfs attributes using SENSOR_TEMPLATE(),
which initializes them as struct sensor_device_attribute (where the index
is a 32-bit int). However, the sysfs callbacks show_pwm() and store_pwm()
incorrectly downcast the attribute to a struct sensor_device_attribute_2
(where the index is an 8-bit u8). Because both structs start with struct
device_attribute, container_of() resolves to the same base address. On
big-endian architectures, reading the 8-bit index field from the memory
layout of a 32-bit int fetches the most significant byte (which is 0),
rather than the intended channel number.
This type mismatch causes all PWM reads to return data for channel 0, and
any writes intended to configure other channels will silently overwrite the
duty cycle of PWM channel 0 instead.

Fix the type casts in show_pwm() and store_pwm() to solve the problem.

Fixes: 41082d66bfd6 ("hwmon: Driver for NCT6683D")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/nct6683.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/nct6683.c b/drivers/hwmon/nct6683.c
index e1c36c95affb..f34cb62305be 100644
--- a/drivers/hwmon/nct6683.c
+++ b/drivers/hwmon/nct6683.c
@@ -920,7 +920,7 @@ static ssize_t
 show_pwm(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	struct nct6683_data *data = nct6683_update_device(dev);
-	struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
+	struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);
 	int index = sattr->index;
 
 	return sprintf(buf, "%d\n", data->pwm[index]);
@@ -930,7 +930,7 @@ static ssize_t
 store_pwm(struct device *dev, struct device_attribute *attr, const char *buf,
 	  size_t count)
 {
-	struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
+	struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);
 	struct nct6683_data *data = dev_get_drvdata(dev);
 	int index = sattr->index;
 	unsigned long val;
-- 
2.45.2