hwmon: (pmbus/core) improve handling of write protected regulators

Writing PMBus protected registers does succeed from the smbus perspective,
even if the write is ignored by the device and a communication fault is
raised. This fault will silently be caught and cleared by pmbus irq if one
has been registered.

This means that the regulator call may return succeed although the
operation was ignored.

With this change, the operation which are not supported will be properly
flagged as such and the regulator framework won't even try to execute them.

Signed-off-by: Jerome Brunet <[email protected]>
[groeck: Adjust to EXPORT_SYMBOL_NS_GPL API change]
Signed-off-by: Guenter Roeck <[email protected]>

Author: jbrun3t

Documentation/hwmon/pmbus-core.rst

@@ -312,6 +312,10 @@ currently provides a flags field with four bits used::
 
 	#define PMBUS_USE_COEFFICIENTS_CMD		BIT(5)
 
+	#define PMBUS_OP_PROTECTED			BIT(6)
+
+	#define PMBUS_VOUT_PROTECTED			BIT(7)
+
 	struct pmbus_platform_data {
 		u32 flags;              /* Device specific flags */
 
@@ -373,3 +377,13 @@ PMBUS_USE_COEFFICIENTS_CMD
 
 When this flag is set the PMBus core driver will use the COEFFICIENTS
 register to initialize the coefficients for the direct mode format.
+
+PMBUS_OP_PROTECTED
+
+Set if the chip OPERATION command is protected and protection is not
+determined by the standard WRITE_PROTECT command.
+
+PMBUS_VOUT_PROTECTED
+
+Set if the chip VOUT_COMMAND command is protected and protection is not
+determined by the standard WRITE_PROTECT command.

drivers/hwmon/pmbus/pmbus.h

@@ -487,6 +487,8 @@ struct pmbus_driver_info {
 /* Regulator ops */
 
 extern const struct regulator_ops pmbus_regulator_ops;
+int pmbus_regulator_init_cb(struct regulator_dev *rdev,
+			    struct regulator_config *config);
 
 /* Macros for filling in array of struct regulator_desc */
 #define PMBUS_REGULATOR_STEP(_name, _id, _voltages, _step, _min_uV)  \
@@ -501,6 +503,7 @@ extern const struct regulator_ops pmbus_regulator_ops;
 		.n_voltages = _voltages,			\
 		.uV_step = _step,				\
 		.min_uV = _min_uV,				\
+		.init_cb = pmbus_regulator_init_cb,		\
 	}
 
 #define PMBUS_REGULATOR(_name, _id)   PMBUS_REGULATOR_STEP(_name, _id, 0, 0, 0)
@@ -516,6 +519,7 @@ extern const struct regulator_ops pmbus_regulator_ops;
 		.n_voltages = _voltages,			\
 		.uV_step = _step,				\
 		.min_uV = _min_uV,				\
+		.init_cb = pmbus_regulator_init_cb,		\
 	}
 
 #define PMBUS_REGULATOR_ONE(_name)   PMBUS_REGULATOR_STEP_ONE(_name, 0, 0, 0)

drivers/hwmon/pmbus/pmbus_core.c

@@ -2665,6 +2665,30 @@ static void pmbus_remove_pec(void *dev)
 	device_remove_file(dev, &dev_attr_pec);
 }
 
+static void pmbus_init_wp(struct i2c_client *client, struct pmbus_data *data)
+{
+	int ret;
+
+	ret = _pmbus_read_byte_data(client, -1, PMBUS_WRITE_PROTECT);
+	if (ret < 0)
+		return;
+
+	switch (ret & PB_WP_ANY) {
+	case PB_WP_ALL:
+		data->flags |= PMBUS_OP_PROTECTED;
+		fallthrough;
+	case PB_WP_OP:
+		data->flags |= PMBUS_VOUT_PROTECTED;
+		fallthrough;
+	case PB_WP_VOUT:
+		data->flags |= PMBUS_WRITE_PROTECTED | PMBUS_SKIP_STATUS_CHECK;
+		break;
+
+	default:
+		break;
+	}
+}
+
 static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 			     struct pmbus_driver_info *info)
 {
@@ -2718,12 +2742,8 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 	 * faults, and we should not try it. Also, in that case, writes into
 	 * limit registers need to be disabled.
 	 */
-	if (!(data->flags & PMBUS_NO_WRITE_PROTECT)) {
-		ret = _pmbus_read_byte_data(client, -1, PMBUS_WRITE_PROTECT);
-
-		if (ret > 0 && (ret & PB_WP_ANY))
-			data->flags |= PMBUS_WRITE_PROTECTED | PMBUS_SKIP_STATUS_CHECK;
-	}
+	if (!(data->flags & PMBUS_NO_WRITE_PROTECT))
+		pmbus_init_wp(client, data);
 
 	ret = i2c_smbus_read_byte_data(client, PMBUS_REVISION);
 	if (ret >= 0)
@@ -3183,8 +3203,12 @@ static int pmbus_regulator_list_voltage(struct regulator_dev *rdev,
 {
 	struct device *dev = rdev_get_dev(rdev);
 	struct i2c_client *client = to_i2c_client(dev->parent);
+	struct pmbus_data *data = i2c_get_clientdata(client);
 	int val, low, high;
 
+	if (data->flags & PMBUS_VOUT_PROTECTED)
+		return 0;
+
 	if (selector >= rdev->desc->n_voltages ||
 	    selector < rdev->desc->linear_min_sel)
 		return -EINVAL;
@@ -3219,6 +3243,22 @@ const struct regulator_ops pmbus_regulator_ops = {
 };
 EXPORT_SYMBOL_NS_GPL(pmbus_regulator_ops, "PMBUS");
 
+int pmbus_regulator_init_cb(struct regulator_dev *rdev,
+			    struct regulator_config *config)
+{
+	struct pmbus_data *data = config->driver_data;
+	struct regulation_constraints *constraints = rdev->constraints;
+
+	if (data->flags & PMBUS_OP_PROTECTED)
+		constraints->valid_ops_mask &= ~REGULATOR_CHANGE_STATUS;
+
+	if (data->flags & PMBUS_VOUT_PROTECTED)
+		constraints->valid_ops_mask &= ~REGULATOR_CHANGE_VOLTAGE;
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(pmbus_regulator_init_cb, "PMBUS");
+
 static int pmbus_regulator_register(struct pmbus_data *data)
 {
 	struct device *dev = data->dev;

include/linux/pmbus.h

@@ -73,6 +73,20 @@
  */
 #define PMBUS_USE_COEFFICIENTS_CMD		BIT(5)
 
+/*
+ * PMBUS_OP_PROTECTED
+ * Set if the chip OPERATION command is protected and protection is not
+ * determined by the standard WRITE_PROTECT command.
+ */
+#define PMBUS_OP_PROTECTED			BIT(6)
+
+/*
+ * PMBUS_VOUT_PROTECTED
+ * Set if the chip VOUT_COMMAND command is protected and protection is not
+ * determined by the standard WRITE_PROTECT command.
+ */
+#define PMBUS_VOUT_PROTECTED			BIT(7)
+
 struct pmbus_platform_data {
 	u32 flags;		/* Device specific flags */