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.
Thanks.
Wei.
>
> Besides that, your delay is unconditional, even for static regulators
> which are always on. Other callers of regulator_enable() don't need
> all that complexity, which I take as sign that it is not needed here either.
>
> Guenter
>
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