On 08/07/2013 03:50 PM, Guenter Roeck wrote:

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On 08/07/2013 12:32 AM, Wei Ni wrote:

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On 08/07/2013 03:27 PM, Alexander Shiyan wrote:

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quoted

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 ++++++++++++++++++++++++++++++++++++++++++++++++++

[...]

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+	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?

I think it should be handled in the device driver.
Because there have different delay time to wait devices stable.

Then why does no other caller of regulator_enable() need this ?
I don't think lm90 is so much different to other users of regulator
functionality.

May be I'm wrong. I noticed that in lm90 SPEC, the max of "SMBus Clock
Low Time" is 25ms, so I supposed that it may need about 20ms to stable
after power on.

Anyway, if I remove this delay, the driver also works fine, so I will
remove it in my next patch.

I originally had in mind that regulator API contain own delay option.
E.g. reg-fixed-voltage && gpio-regulator contains "startup-delay-us" property.

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