hwmon: (pmbus/tda38640) Add workaround for SVID mode

TDA38640 can operate in either PMBus mode or SVID mode.

In SVID mode, by design ENABLE pin is the only option for controlling
the output rail i.e., ENABLE pin is chained to power good of another
reglator & FPGA.

In cases where the chip is configured for SVID mode, and the ENABLE pin
is set at a fixed level or is left unconnected (with an internal
pull-down), while requiring software control, the following
workaround is necessary.

The workaround utilizes ENABLE pin polarity flipping to control
output rail.

If property 'infineon,en-pin-fixed-level' is specified then
determine if chip is in SVID mode by checking BIT15 of MTP memory offset
0x44 as described in the datasheet.

If chip is in SVID mode then apply the workaround by
1. Determine EN pin level
2. Maps BIT7 of OPERATION(01h) to EN_PIN_POLARITY(BIT1) of
   PB_ON_OFF_CONFIG.
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Link: https://lore.kernel.org/r/20230831190731.265099-3-Naresh.Solanki@9elements.com
[groeck: Dropped unnecessary line continuation]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/tda38640.c

@@ -18,6 +18,127 @@ 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 int svid_mode(struct i2c_client *client, struct tda38640_data *data)
+{
+	/* PMBUS_MFR_READ(0xD0) + MTP Address offset */
+	u8 write_buf[] = {0xd0, 0x44, 0x00};
+	u8 read_buf[2];
+	int ret, svid;
+	bool off, reg_en_pin_pol;
+
+	struct i2c_msg msgs[2] = {
+		{
+			.addr = client->addr,
+			.flags = 0,
+			.buf = write_buf,
+			.len = sizeof(write_buf),
+		},
+		{
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.buf = read_buf,
+			.len = sizeof(read_buf),
+		}
+	};
+
+	ret = i2c_transfer(client->adapter, msgs, 2);
+	if (ret < 0) {
+		dev_err(&client->dev, "i2c_transfer failed. %d", ret);
+		return ret;
+	}
+
+	/*
+	 * 0x44[15] determines PMBus Operating Mode
+	 * If bit is set then it is SVID mode.
+	 */
+	svid = !!(read_buf[1] & BIT(7));
+
+	/*
+	 * Determine EN pin level for use in SVID mode.
+	 * This is done with help of STATUS_BYTE bit 6(OFF) & ON_OFF_CONFIG bit 2(EN pin polarity).
+	 */
+	if (svid) {
+		ret = i2c_smbus_read_byte_data(client, PMBUS_STATUS_BYTE);
+		if (ret < 0)
+			return ret;
+		off = !!(ret & PB_STATUS_OFF);
+
+		ret = i2c_smbus_read_byte_data(client, PMBUS_ON_OFF_CONFIG);
+		if (ret < 0)
+			return ret;
+		reg_en_pin_pol = !!(ret & PB_ON_OFF_CONFIG_POLARITY_HIGH);
+		data->en_pin_lvl = off ^ reg_en_pin_pol;
+	}
+
+	return svid;
+}
+
 static struct pmbus_driver_info tda38640_info = {
 	.pages = 1,
 	.format[PSC_VOLTAGE_IN] = linear,
@@ -26,7 +147,6 @@ 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 +161,37 @@ static struct pmbus_driver_info tda38640_info = {
 
 static int tda38640_probe(struct i2c_client *client)
 {
-	return pmbus_do_probe(client, &tda38640_info);
+	struct tda38640_data *data;
+	int svid;
+
+	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	memcpy(&data->info, &tda38640_info, sizeof(tda38640_info));
+
+	if (IS_ENABLED(CONFIG_SENSORS_TDA38640_REGULATOR) &&
+	    of_property_read_bool(client->dev.of_node, "infineon,en-pin-fixed-level")) {
+		svid = svid_mode(client, data);
+		if (svid < 0) {
+			dev_err_probe(&client->dev, svid, "Could not determine operating mode.");
+			return svid;
+		}
+
+		/*
+		 * Apply ON_OFF_CONFIG workaround as enabling the regulator using the
+		 * OPERATION register doesn't work in SVID mode.
+		 *
+		 * One should configure PMBUS_ON_OFF_CONFIG here, but
+		 * PB_ON_OFF_CONFIG_POWERUP_CONTROL and PB_ON_OFF_CONFIG_EN_PIN_REQ
+		 * are ignored by the device.
+		 * Only PB_ON_OFF_CONFIG_POLARITY_HIGH has an effect.
+		 */
+		if (svid) {
+			data->info.read_byte_data = tda38640_read_byte_data;
+			data->info.write_byte_data = tda38640_write_byte_data;
+		}
+	}
+	return pmbus_do_probe(client, &data->info);
 }
 
 static const struct i2c_device_id tda38640_id[] = {