On 08/07/2013 03:35 AM, Wei Ni wrote:
> On 08/07/2013 04:45 PM, Alexander Shiyan wrote:
>>> On 08/07/2013 03:50 PM, Guenter Roeck wrote:
>>>> On 08/07/2013 12:32 AM, Wei Ni wrote:
>>>>> On 08/07/2013 03:27 PM, Alexander Shiyan wrote:
>>>>>>> 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 <wni@xxxxxxxxxx>
>>>>>>> ---
>>>>>>> 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?
>>>>>
>>>>> 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.
>
> As I know the "startup-delay-us" is used for the regulator device, not
> the consumer devices.
Yes, the regulator should encoded its own startup delay. Each individual
device should handle its own requirements for delay after power is stable.
> In this patch, msleep(POWER_ON_DELAY) was used to wait the lm90 stable,
> but it seems it's unnecessary now :)
No, the driver needs to handle this properly. If the datasheet says a
delay is needed, it is.
It's probably working because in your tests the supply just happens to
be on already.
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