[PATCH 3/3] hwmon: (pmbus/tda38640) Add workaround for bug in SVID mode

[Naresh Solanki <naresh.solanki@9elements.com>]

From: Patrick Rudolph <patrick.rudolph@9elements.com>

The TDA38640 supports two operating modes to set the output voltage:
- PMBUS
- SVID

Due to an undocumented bug the regulator cannot be enabled using BIT7
of OPERATION(01h) register when in SVID mode.
It works when in PMBUS mode. In SVID mode the regulator only cares
about the ENABLE pin.

Add a workaround that needs the ENABLE pin to be left floating or
tied to a fixed level. The DT must contain the newly introduced
property 'infineon,en-pin-fixed-level' to enable this workaround.

The workaround will map the PB_OPERATION_CONTROL_ON bit to the
PB_ON_OFF_CONFIG_EN_PIN_REQ bit of the ON_OFF_CONFIG register.
In combination with the fixed level on the ENABLE pin the regulator
can be controlled as expected.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
---
 drivers/hwmon/pmbus/tda38640.c | 95 +++++++++++++++++++++++++++++++++-
 1 file changed, 93 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/pmbus/tda38640.c b/drivers/hwmon/pmbus/tda38640.c
index 450b0273fb59..9d3b89d9845c 100644
--- a/drivers/hwmon/pmbus/tda38640.c
+++ b/drivers/hwmon/pmbus/tda38640.c
@@ -18,6 +18,72 @@ static const struct regulator_desc __maybe_unused tda38640_reg_desc[] = {
 	PMBUS_REGULATOR("vout", 0),
 };
 
+struct tda38640_data {
+	struct pmbus_driver_info info;
+	u32 en_pin_lvl;
+};
+
+#define to_tda38640_data(x)  container_of(x, struct tda38640_data, info)
+
+/*
+ * Map PB_ON_OFF_CONFIG_POLARITY_HIGH to PB_OPERATION_CONTROL_ON.
+ */
+static int tda38640_read_byte_data(struct i2c_client *client, int page, int reg)
+{
+	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
+	struct tda38640_data *data = to_tda38640_data(info);
+	int ret, on_off_config, enabled;
+
+	if (reg != PMBUS_OPERATION)
+		return -ENODATA;
+
+	ret = pmbus_read_byte_data(client, page, reg);
+	if (ret < 0)
+		return ret;
+
+	on_off_config = pmbus_read_byte_data(client, page,
+					     PMBUS_ON_OFF_CONFIG);
+	if (on_off_config < 0)
+		return on_off_config;
+
+	enabled = !!(on_off_config & PB_ON_OFF_CONFIG_POLARITY_HIGH);
+
+	enabled ^= data->en_pin_lvl;
+	if (enabled)
+		ret &= ~PB_OPERATION_CONTROL_ON;
+	else
+		ret |= PB_OPERATION_CONTROL_ON;
+
+	return ret;
+}
+
+/*
+ * Map PB_OPERATION_CONTROL_ON to PB_ON_OFF_CONFIG_POLARITY_HIGH.
+ */
+static int tda38640_write_byte_data(struct i2c_client *client, int page,
+				    int reg, u8 byte)
+{
+	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
+	struct tda38640_data *data = to_tda38640_data(info);
+	int enable, ret;
+
+	if (reg != PMBUS_OPERATION)
+		return -ENODATA;
+
+	enable = !!(byte & PB_OPERATION_CONTROL_ON);
+
+	byte &= ~PB_OPERATION_CONTROL_ON;
+	ret = pmbus_write_byte_data(client, page, reg, byte);
+	if (ret < 0)
+		return ret;
+
+	enable ^= data->en_pin_lvl;
+
+	return pmbus_update_byte_data(client, page, PMBUS_ON_OFF_CONFIG,
+				      PB_ON_OFF_CONFIG_POLARITY_HIGH,
+				      enable ? 0 : PB_ON_OFF_CONFIG_POLARITY_HIGH);
+}
+
 static struct pmbus_driver_info tda38640_info = {
 	.pages = 1,
 	.format[PSC_VOLTAGE_IN] = linear,
@@ -26,7 +92,6 @@ static struct pmbus_driver_info tda38640_info = {
 	.format[PSC_CURRENT_IN] = linear,
 	.format[PSC_POWER] = linear,
 	.format[PSC_TEMPERATURE] = linear,
-
 	.func[0] = PMBUS_HAVE_VIN | PMBUS_HAVE_STATUS_INPUT
 	    | PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP
 	    | PMBUS_HAVE_IIN
@@ -41,7 +106,33 @@ static struct pmbus_driver_info tda38640_info = {
 
 static int tda38640_probe(struct i2c_client *client)
 {
-	return pmbus_do_probe(client, &tda38640_info);
+	struct device *dev = &client->dev;
+	struct device_node *np = dev_of_node(dev);
+	struct tda38640_data *data;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	memcpy(&data->info, &tda38640_info, sizeof(tda38640_info));
+
+	if (!CONFIG_SENSORS_TDA38640_REGULATOR || !np ||
+	    of_property_read_u32(np, "infineon,en-pin-fixed-level", &data->en_pin_lvl))
+		return pmbus_do_probe(client, &data->info);
+
+	/*
+	 * Apply ON_OFF_CONFIG workaround as enabling the regulator using the
+	 * OPERATION register doesn't work in SVID mode.
+	 */
+	data->info.read_byte_data = tda38640_read_byte_data;
+	data->info.write_byte_data = tda38640_write_byte_data;
+	/*
+	 * One should configure PMBUS_ON_OFF_CONFIG here, but
+	 * PB_ON_OFF_CONFIG_POWERUP_CONTROL, PB_ON_OFF_CONFIG_EN_PIN_REQ and
+	 * PB_ON_OFF_CONFIG_EN_PIN_REQ are ignored by the device.
+	 * Only PB_ON_OFF_CONFIG_POLARITY_HIGH has an effect.
+	 */
+
+	return pmbus_do_probe(client, &data->info);
 }
 
 static const struct i2c_device_id tda38640_id[] = {
-- 
2.41.0