hwmon: (pmbus/core) add wp module param

Add a module parameter to force the write protection mode of pmbus chips.

4 protections modes are provided to start with:
* 0: Remove the write protection
* 1: Disable all writes except to the WRITE_PROTECT, OPERATION,
     PAGE, ON_OFF_CONFIG and VOUT_COMMAND commands
* 2: Disable all writes except to the WRITE_PROTECT, OPERATION and
     PAGE commands
* 3: Disable all writes except to the WRITE_PROTECT command

Of course, if the parameter is not provided, the default write protection
status of the pmbus chips is left untouched.

Suggested-by: Guenter Roeck <[email protected]>
Signed-off-by: Jerome Brunet <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>

Author: jbrun3t

Documentation/hwmon/pmbus-core.rst

@@ -387,3 +387,24 @@ PMBUS_VOUT_PROTECTED
 
 Set if the chip VOUT_COMMAND command is protected and protection is not
 determined by the standard WRITE_PROTECT command.
+
+Module parameter
+----------------
+
+pmbus_core.wp: PMBus write protect forced mode
+
+PMBus may come up with a variety of write protection configuration.
+'pmbus_core.wp' may be used if a particular write protection is necessary.
+The ability to actually alter the protection may also depend on the chip
+so the actual runtime write protection configuration may differ from
+the requested one. pmbus_core currently support the following value:
+
+* 0: write protection removed.
+* 1: Disable all writes except to the WRITE_PROTECT, OPERATION,
+  PAGE, ON_OFF_CONFIG and VOUT_COMMAND commands.
+* 2: Disable all writes except to the WRITE_PROTECT, OPERATION and
+  PAGE commands.
+* 3: Disable all writes except to the WRITE_PROTECT command. Note that
+  protection should include the PAGE register. This may be problematic
+  for multi-page chips, if the chips strictly follows the PMBus
+  specification, preventing the chip from changing the active page.

drivers/hwmon/pmbus/pmbus_core.c

@@ -31,6 +31,9 @@
 #define PMBUS_ATTR_ALLOC_SIZE	32
 #define PMBUS_NAME_SIZE		24
 
+static int wp = -1;
+module_param(wp, int, 0444);
+
 struct pmbus_sensor {
 	struct pmbus_sensor *next;
 	char name[PMBUS_NAME_SIZE];	/* sysfs sensor name */
@@ -2669,6 +2672,32 @@ static void pmbus_init_wp(struct i2c_client *client, struct pmbus_data *data)
 {
 	int ret;
 
+	switch (wp) {
+	case 0:
+		_pmbus_write_byte_data(client, -1,
+				       PMBUS_WRITE_PROTECT, 0);
+		break;
+
+	case 1:
+		_pmbus_write_byte_data(client, -1,
+				       PMBUS_WRITE_PROTECT, PB_WP_VOUT);
+		break;
+
+	case 2:
+		_pmbus_write_byte_data(client, -1,
+				       PMBUS_WRITE_PROTECT, PB_WP_OP);
+		break;
+
+	case 3:
+		_pmbus_write_byte_data(client, -1,
+				       PMBUS_WRITE_PROTECT, PB_WP_ALL);
+		break;
+
+	default:
+		/* Ignore the other values */
+		break;
+	}
+
 	ret = _pmbus_read_byte_data(client, -1, PMBUS_WRITE_PROTECT);
 	if (ret < 0)
 		return;