[PATCH] hwmon: (max6639) : Allow setting target RPM

[Your Name <naresh.solanki@9elements.com>]

From: Naresh Solanki <naresh.solanki@9elements.com>

Currently, during startup, the fan is set to its maximum RPM by default,
which may not be suitable for all use cases.
This patch introduces support for specifying a target RPM via the Device
Tree property "target-rpm".

Changes:
- Added `target_rpm` field to `max6639_data` structure to store the
  target RPM for each fan channel.
- Modified `max6639_probe_child_from_dt()` to read the `"target-rpm"`
  property from the Device Tree and set `target_rpm` accordingly.
- Updated `max6639_init_client()` to use `target_rpm` to compute the
  initial PWM duty cycle instead of defaulting to full speed (120/120).

Behavior:
- If `"target-rpm"` is specified, the fan speed is set accordingly.
- If `"target-rpm"` is not specified, the previous behavior (full speed
  at startup) is retained.

This allows better control over fan speed during system initialization.

Signed-off-by: Naresh Solanki <naresh.solanki@9elements.com>
---
 drivers/hwmon/max6639.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/max6639.c b/drivers/hwmon/max6639.c
index 32b4d54b2076..ca8a8f58d133 100644
--- a/drivers/hwmon/max6639.c
+++ b/drivers/hwmon/max6639.c
@@ -80,6 +80,7 @@ struct max6639_data {
 	/* Register values initialized only once */
 	u8 ppr[MAX6639_NUM_CHANNELS];	/* Pulses per rotation 0..3 for 1..4 ppr */
 	u8 rpm_range[MAX6639_NUM_CHANNELS]; /* Index in above rpm_ranges table */
+	u32 target_rpm[MAX6639_NUM_CHANNELS];
 
 	/* Optional regulator for FAN supply */
 	struct regulator *reg;
@@ -560,8 +561,14 @@ static int max6639_probe_child_from_dt(struct i2c_client *client,
 	}
 
 	err = of_property_read_u32(child, "max-rpm", &val);
-	if (!err)
+	if (!err) {
 		data->rpm_range[i] = rpm_range_to_reg(val);
+		data->target_rpm[i] = val;
+	}
+
+	err = of_property_read_u32(child, "target-rpm", &val);
+	if (!err)
+		data->target_rpm[i] = val;
 
 	return 0;
 }
@@ -573,6 +580,7 @@ static int max6639_init_client(struct i2c_client *client,
 	const struct device_node *np = dev->of_node;
 	struct device_node *child;
 	int i, err;
+	u8 target_duty;
 
 	/* Reset chip to default values, see below for GCONFIG setup */
 	err = regmap_write(data->regmap, MAX6639_REG_GCONFIG, MAX6639_GCONFIG_POR);
@@ -639,8 +647,9 @@ static int max6639_init_client(struct i2c_client *client,
 		if (err)
 			return err;
 
-		/* PWM 120/120 (i.e. 100%) */
-		err = regmap_write(data->regmap, MAX6639_REG_TARGTDUTY(i), 120);
+		/* Set PWM based on target RPM if specified */
+		target_duty = 120 * data->target_rpm[i] / rpm_ranges[data->rpm_range[i]];
+		err = regmap_write(data->regmap, MAX6639_REG_TARGTDUTY(i), target_duty);
 		if (err)
 			return err;
 	}

base-commit: 2115cbeec8a3ccc69e3b7ecdf97b4472b0829cfc
-- 
2.42.0