The device lm90 can be controlled by the vdd rail.
Adding the power control support to power on/off the vdd rail.
And make sure that power is enabled before accessing the device.

Signed-off-by: Wei Ni <redacted>
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 drivers/hwmon/lm90.c |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++

[...]

+	if (!data->lm90_reg) {
+		data->lm90_reg = regulator_get(&client->dev, "vdd");
+		if (IS_ERR_OR_NULL(data->lm90_reg)) {
+			if (PTR_ERR(data->lm90_reg) == -ENODEV)
+				dev_info(&client->dev,
+					 "No regulator found for vdd. Assuming vdd is always powered.");
+			else
+				dev_warn(&client->dev,
+					 "Error [%ld] in getting the regulator handle for vdd.\n",
+					 PTR_ERR(data->lm90_reg));
+			data->lm90_reg = NULL;
+			mutex_unlock(&data->update_lock);
+			return -ENODEV;
+		}
+	}
+	if (is_enable) {
+		ret = regulator_enable(data->lm90_reg);
+		msleep(POWER_ON_DELAY);

Can this delay be handled directly from regulator?

[...]
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