regulator: TPS6287X: Use min/max uV to get VRANGE

Changing voltage might ignore slew rate and cause a current surge.

With current implementation the driver will get the regulator to change
the voltage range used during run time. According to communication I
have had with Texas Instruments, this is not intended, since the
Dynamic Voltage Scaling in the hardware is only designed to work
within a voltage range. The current implementation will therefore
ignore the slew rate that is defined in devicetree when the voltage
range is changed during use.

The current implementation will always select a voltage in the most
accurate range that can reach that voltage even though multiple ranges
are able to reach that voltage. There are 4 Voltage ranges with the
following reach:
0b00: 0.4-0.71875V      (1.25mV step size)
0b01: 0.4-1.0375V       (2.5mV)
0b10: 0.4-1.675V        (5mV)
0b11: 0.8-3.3V          (10mV)
This in practice means that a change from below to above 0.71875V will
use the smallest range(0b00) for the values below and the second
smallest range(0b01) for the voltages above (Up to 1.675V). I have
timed how long it takes to go from below 0.71875V to above. The
increase was 100mV which, with the slew rate set to 1250µV/µs. This
in theory should take 80µs to do. With the current implementation, it
takes 10µs on my hardware. Doing the same test with the slew rate set
to 5000µV/µs, which should take 20µs, also only takes 10µs to do on
my hardware. Not only is this not in line with the technical
specification for the regulator. It also causes a current surge. Which
when calculating the output current, as described in the technical
specification, compared to what I could observe on my hardware the real
output is ~1A higher (~1.2A) than what I calculated it to be(~0.2A).

I tested also transitioning from a bigger to a smaller range, and the
results were the same.

Instead, let's limit the voltage range to a single one, which is in
line with the intended use of the regulator. This is done by looking
up the minimum and maximum requested voltage specified in devicetree.

Signed-off-by: Jonas Andreasson <jonas.andreasson@axis.com>
Link: https://patch.msgid.link/20250121-tps-fix-v2-1-50cc4d0f1635@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Jonas Andreasson

drivers/regulator/tps6287x-regulator.c

@@ -44,10 +44,35 @@ static const unsigned int tps6287x_voltage_range_sel[] = {
 	0x0, 0x1, 0x2, 0x3
 };
 
+static const unsigned int tps6287x_voltage_range_prefix[] = {
+	0x000, 0x100, 0x200, 0x300
+};
+
 static const unsigned int tps6287x_ramp_table[] = {
 	10000, 5000, 1250, 500
 };
 
+struct tps6287x_reg_data {
+	int range;
+};
+
+static int tps6287x_best_range(struct regulator_config *config, const struct regulator_desc *desc)
+{
+	const struct linear_range *r;
+	int i;
+
+	if (!config->init_data->constraints.apply_uV)
+		return -1;
+
+	for (i = 0; i < desc->n_linear_ranges; i++) {
+		r = &desc->linear_ranges[i];
+		if (r->min <= config->init_data->constraints.min_uV &&
+		    config->init_data->constraints.max_uV <= linear_range_get_max_value(r))
+			return i;
+	}
+	return -1;
+}
+
 static int tps6287x_set_mode(struct regulator_dev *rdev, unsigned int mode)
 {
 	unsigned int val;
@@ -91,6 +116,28 @@ static unsigned int tps6287x_of_map_mode(unsigned int mode)
 	}
 }
 
+static int tps6287x_map_voltage(struct regulator_dev *rdev, int min_uV, int max_uV)
+{
+	struct tps6287x_reg_data *data = (struct tps6287x_reg_data *)rdev->reg_data;
+	struct linear_range selected_range;
+	int selector, voltage;
+
+	if (!data || data->range == -1)
+		return regulator_map_voltage_pickable_linear_range(rdev, min_uV, max_uV);
+
+	selected_range = rdev->desc->linear_ranges[data->range];
+	selector = DIV_ROUND_UP(min_uV - selected_range.min, selected_range.step);
+	if (selector < selected_range.min_sel || selector > selected_range.max_sel)
+		return -EINVAL;
+
+	selector |= tps6287x_voltage_range_prefix[data->range];
+	voltage = rdev->desc->ops->list_voltage(rdev, selector);
+	if (voltage < min_uV || voltage > max_uV)
+		return -EINVAL;
+
+	return selector;
+}
+
 static const struct regulator_ops tps6287x_regulator_ops = {
 	.enable = regulator_enable_regmap,
 	.disable = regulator_disable_regmap,
@@ -100,6 +147,7 @@ static const struct regulator_ops tps6287x_regulator_ops = {
 	.get_voltage_sel = regulator_get_voltage_sel_pickable_regmap,
 	.set_voltage_sel = regulator_set_voltage_sel_pickable_regmap,
 	.list_voltage = regulator_list_voltage_pickable_linear_range,
+	.map_voltage = tps6287x_map_voltage,
 	.set_ramp_delay = regulator_set_ramp_delay_regmap,
 };
 
@@ -130,8 +178,14 @@ static int tps6287x_i2c_probe(struct i2c_client *i2c)
 {
 	struct device *dev = &i2c->dev;
 	struct regulator_config config = {};
+	struct tps6287x_reg_data *reg_data;
 	struct regulator_dev *rdev;
 
+	reg_data = devm_kzalloc(dev, sizeof(struct tps6287x_reg_data), GFP_KERNEL);
+
+	if (!reg_data)
+		return -ENOMEM;
+
 	config.regmap = devm_regmap_init_i2c(i2c, &tps6287x_regmap_config);
 	if (IS_ERR(config.regmap)) {
 		dev_err(dev, "Failed to init i2c\n");
@@ -143,12 +197,15 @@ static int tps6287x_i2c_probe(struct i2c_client *i2c)
 	config.init_data = of_get_regulator_init_data(dev, dev->of_node,
 						      &tps6287x_reg);
 
+	reg_data->range = tps6287x_best_range(&config, &tps6287x_reg);
+
 	rdev = devm_regulator_register(dev, &tps6287x_reg, &config);
 	if (IS_ERR(rdev)) {
 		dev_err(dev, "Failed to register regulator\n");
 		return PTR_ERR(rdev);
 	}
 
+	rdev->reg_data = (void *)reg_data;
 	dev_dbg(dev, "Probed regulator\n");
 
 	return 0;