hwmon: (pmbus/core) Prevent unintentional setting of page to 0xFF

The pmbus core may call read/write word data functions with a page value
of -1, intending to perform the operation without setting the page.
However, the read/write word data functions accept only unsigned 8-bit
page numbers, and therefore cannot check for negative page number to
avoid setting the page. This results in setting the page number to 0xFF.
This may result in errors or undefined behavior of some devices
(specifically the ir35221, which allows the page to be set to 0xFF,
but some subsequent operations to read registers may fail).

Switch the pmbus_set_page page parameter to an integer and perform the
check for negative page there. Make read/write functions consistent in
accepting an integer page number parameter.
Signed-off-by: NEdward A. James <eajames@us.ibm.com>
Fixes: cbcdec62 ("hwmon: (pmbus): Access word data for STATUS_WORD")
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/pmbus.h

@@ -404,9 +404,9 @@ extern const struct regulator_ops pmbus_regulator_ops;
 /* Function declarations */
 
 void pmbus_clear_cache(struct i2c_client *client);
-int pmbus_set_page(struct i2c_client *client, u8 page);
-int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg);
-int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, u16 word);
+int pmbus_set_page(struct i2c_client *client, int page);
+int pmbus_read_word_data(struct i2c_client *client, int page, u8 reg);
+int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg, u16 word);
 int pmbus_read_byte_data(struct i2c_client *client, int page, u8 reg);
 int pmbus_write_byte(struct i2c_client *client, int page, u8 value);
 int pmbus_write_byte_data(struct i2c_client *client, int page, u8 reg,

drivers/hwmon/pmbus/pmbus_core.c

@@ -136,13 +136,13 @@ void pmbus_clear_cache(struct i2c_client *client)
 }
 EXPORT_SYMBOL_GPL(pmbus_clear_cache);
 
-int pmbus_set_page(struct i2c_client *client, u8 page)
+int pmbus_set_page(struct i2c_client *client, int page)
 {
 	struct pmbus_data *data = i2c_get_clientdata(client);
 	int rv = 0;
 	int newpage;
 
-	if (page != data->currpage) {
+	if (page >= 0 && page != data->currpage) {
 		rv = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
 		newpage = i2c_smbus_read_byte_data(client, PMBUS_PAGE);
 		if (newpage != page)
@@ -158,11 +158,9 @@ int pmbus_write_byte(struct i2c_client *client, int page, u8 value)
 {
 	int rv;
 
-	if (page >= 0) {
-		rv = pmbus_set_page(client, page);
-		if (rv < 0)
-			return rv;
-	}
+	rv = pmbus_set_page(client, page);
+	if (rv < 0)
+		return rv;
 
 	return i2c_smbus_write_byte(client, value);
 }
@@ -186,7 +184,8 @@ static int _pmbus_write_byte(struct i2c_client *client, int page, u8 value)
 	return pmbus_write_byte(client, page, value);
 }
 
-int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, u16 word)
+int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg,
+			  u16 word)
 {
 	int rv;
 
@@ -219,7 +218,7 @@ static int _pmbus_write_word_data(struct i2c_client *client, int page, int reg,
 	return pmbus_write_word_data(client, page, reg, word);
 }
 
-int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg)
+int pmbus_read_word_data(struct i2c_client *client, int page, u8 reg)
 {
 	int rv;
 
@@ -255,11 +254,9 @@ int pmbus_read_byte_data(struct i2c_client *client, int page, u8 reg)
 {
 	int rv;
 
-	if (page >= 0) {
-		rv = pmbus_set_page(client, page);
-		if (rv < 0)
-			return rv;
-	}
+	rv = pmbus_set_page(client, page);
+	if (rv < 0)
+		return rv;
 
 	return i2c_smbus_read_byte_data(client, reg);
 }