On Wed, Aug 07, 2013 at 10:06:30AM -0600, Stephen Warren wrote:
> 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 <w...@nvidia.com>
> >>>>>>> ---
> >>>>>>> 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.
>
Yes but, if at all, only if it is known that the supply has just been turned on.
Imposing the delay on every user of the driver is unacceptable.
Guenter
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