[PATCH v3 3/5] 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>

---
v3:
  - droped comments and indexed the table with enums instead
  - use device_property_read_u32() instead of_property_read_u32()
v2:
  - renamed property to mps,vout-fb-divider-ratio-permille
  - added register value range checking
---
 drivers/hwmon/pmbus/mpq8785.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/hwmon/pmbus/mpq8785.c b/drivers/hwmon/pmbus/mpq8785.c
index d0ac294b4bbc..2e7c0d0c3f81 100644
--- a/drivers/hwmon/pmbus/mpq8785.c
+++ b/drivers/hwmon/pmbus/mpq8785.c
@@ -5,11 +5,16 @@
 
 #include <linux/i2c.h>
 #include <linux/module.h>
+#include <linux/property.h>
 #include <linux/of_device.h>
 #include "pmbus.h"
 
 enum chips { mpq8785 };
 
+static u16 voltage_scale_loop_max_val[] = {
+	[mpq8785] = GENMASK(10, 0),
+};
+
 static int mpq8785_identify(struct i2c_client *client,
 			    struct pmbus_driver_info *info)
 {
@@ -74,6 +79,8 @@ 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)
@@ -92,6 +99,17 @@ static int mpq8785_probe(struct i2c_client *client)
 		return -ENODEV;
 	}
 
+	if (!device_property_read_u32(dev, "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