[PATCH v4 2/2] hwmon: pmbus: max20730: adjust the vout reading given voltage divider

[Chu Lin <linchuyuan@google.com>]

Problem:
We use voltage dividers so that the voltage presented at the voltage
sense pins is confusing. We might need to convert these readings to more
meaningful readings given the voltage divider.

Solution:
Read the voltage divider resistance from dts and convert the voltage
reading to a more meaningful reading.

Testing:
max20730 with voltage divider

Signed-off-by: Chu Lin <linchuyuan@google.com>
---
ChangeLog v1 -> v2
  hwmon: pmbus: max20730:
  - Don't do anything to the ret if an error is returned from pmbus_read_word
  - avoid overflow when doing multiplication

ChangeLog v2 -> v3
  dt-bindings: hwmon: max20730:
  - Provide the binding documentation in yaml format
  hwmon: pmbus: max20730:
  - No change

ChangeLog v3 -> v4
  dt-bindings: hwmon: max20730:
  - Fix highefficiency to high efficiency in description
  - Fix presents to present in vout-voltage-divider
  - Add additionalProperties: false
  hwmon: pmbus: max20730:
  - No change

 drivers/hwmon/pmbus/max20730.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/hwmon/pmbus/max20730.c b/drivers/hwmon/pmbus/max20730.c
index a151a2b588a5..fbf2f1e6c969 100644
--- a/drivers/hwmon/pmbus/max20730.c
+++ b/drivers/hwmon/pmbus/max20730.c
@@ -31,6 +31,7 @@ struct max20730_data {
 	struct pmbus_driver_info info;
 	struct mutex lock;	/* Used to protect against parallel writes */
 	u16 mfr_devset1;
+	u32 vout_voltage_divider[2];
 };
 
 #define to_max20730_data(x)  container_of(x, struct max20730_data, info)
@@ -114,6 +115,14 @@ static int max20730_read_word_data(struct i2c_client *client, int page,
 		max_c = max_current[data->id][(data->mfr_devset1 >> 5) & 0x3];
 		ret = val_to_direct(max_c, PSC_CURRENT_OUT, info);
 		break;
+	case PMBUS_READ_VOUT:
+		ret = pmbus_read_word_data(client, page, phase, reg);
+		if (ret > 0 && data->vout_voltage_divider[0] && data->vout_voltage_divider[1]) {
+			u64 temp = DIV_ROUND_CLOSEST_ULL((u64)ret * data->vout_voltage_divider[1],
+							 data->vout_voltage_divider[0]);
+			ret = clamp_val(temp, 0, 0xffff);
+		}
+		break;
 	default:
 		ret = -ENODATA;
 		break;
@@ -364,6 +373,15 @@ static int max20730_probe(struct i2c_client *client,
 	data->id = chip_id;
 	mutex_init(&data->lock);
 	memcpy(&data->info, &max20730_info[chip_id], sizeof(data->info));
+	if (of_property_read_u32_array(client->dev.of_node, "vout-voltage-divider",
+				       data->vout_voltage_divider,
+				       ARRAY_SIZE(data->vout_voltage_divider)) != 0)
+		memset(data->vout_voltage_divider, 0, sizeof(data->vout_voltage_divider));
+	if (data->vout_voltage_divider[1] < data->vout_voltage_divider[0]) {
+		dev_err(dev,
+			"The total resistance of voltage divider is less than output resistance\n");
+		return -ENODEV;
+	}
 
 	ret = i2c_smbus_read_word_data(client, MAX20730_MFR_DEVSET1);
 	if (ret < 0)
-- 
2.28.0.806.g8561365e88-goog