From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/2] hwmon: (lm90) Add power control
Date: Wed, 07 Aug 2013 10:06:30 -0600 [thread overview]
Message-ID: <52027086.1090608@wwwdotorg.org> (raw)
In-Reply-To: <520214C9.1010200@nvidia.com>
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@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.
It's probably working because in your tests the supply just happens to
be on already.
next prev parent reply other threads:[~2013-08-07 16:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-07 6:52 [PATCH 0/2] Add power control for lm90 Wei Ni
2013-08-07 6:52 ` [PATCH 1/2] hwmon: (lm90) Add power control Wei Ni
2013-08-07 7:03 ` Guenter Roeck
2013-08-07 7:15 ` Wei Ni
2013-08-07 7:27 ` Alexander Shiyan
2013-08-07 7:32 ` Wei Ni
2013-08-07 7:50 ` Guenter Roeck
2013-08-07 8:07 ` Wei Ni
2013-08-07 8:45 ` Alexander Shiyan
2013-08-07 9:35 ` Wei Ni
2013-08-07 16:06 ` Stephen Warren [this message]
2013-08-07 16:44 ` Guenter Roeck
2013-08-07 7:45 ` Guenter Roeck
2013-08-07 6:52 ` [PATCH 2/2] ARM: dt: t114 dalmore: add dt entry for nct1008 Wei Ni
2013-08-07 16:03 ` Stephen Warren
2013-08-08 2:36 ` Wei Ni
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