[PATCH v2 4/5] hwmon: pmbus: mpq8785: Implement VOUT feedback resistor divider ratio configuration

[Pawel Dembicki <paweldembicki@gmail.com>]

Implement support for setting the VOUT_SCALE_LOOP PMBus register
based on an optional device tree property
"mps,vout-fb-divider-ratio-permille".

This allows the driver to provide the correct VOUT value depending
on the feedback voltage divider configuration for chips where the
bootloader does not configure the VOUT_SCALE_LOOP register.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>

---
v2:
  - rename property to mps,vout-fb-divider-ratio-permille
  - add register value range checking
---
 drivers/hwmon/pmbus/mpq8785.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/hwmon/pmbus/mpq8785.c b/drivers/hwmon/pmbus/mpq8785.c
index 34245d0d2125..1d0e7ac9daf4 100644
--- a/drivers/hwmon/pmbus/mpq8785.c
+++ b/drivers/hwmon/pmbus/mpq8785.c
@@ -12,6 +12,13 @@
 
 enum chips { mpq8785, mpm82504, mpm3695, mpm3695_25 };
 
+static u16 voltage_scale_loop_max_val[] = {
+	GENMASK(10, 0), /* mpq8785 */
+	GENMASK(9, 0), /* mpm82504 */
+	GENMASK(9, 0), /* mpm3695 */
+	GENMASK(11, 0), /* mpm3695_25 */
+};
+
 static int mpq8785_identify(struct i2c_client *client,
 			    struct pmbus_driver_info *info)
 {
@@ -99,6 +106,8 @@ static int mpq8785_probe(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	struct pmbus_driver_info *info;
 	enum chips chip_id;
+	u32 voltage_scale;
+	int ret;
 
 	info = devm_kmemdup(dev, &mpq8785_info, sizeof(*info), GFP_KERNEL);
 	if (!info)
@@ -126,6 +135,18 @@ static int mpq8785_probe(struct i2c_client *client)
 		return -ENODEV;
 	}
 
+	if (!of_property_read_u32(dev->of_node,
+				  "mps,vout-fb-divider-ratio-permille",
+				  &voltage_scale)) {
+		if (voltage_scale > voltage_scale_loop_max_val[chip_id])
+			return -EINVAL;
+
+		ret = i2c_smbus_write_word_data(client, PMBUS_VOUT_SCALE_LOOP,
+						voltage_scale);
+		if (ret)
+			return ret;
+	}
+
 	return pmbus_do_probe(client, info);
 };
 
-- 
2.43.0