From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH 1/2] hwmon: (lm90) Add power control Date: Wed, 07 Aug 2013 10:06:30 -0600 Message-ID: <52027086.1090608@wwwdotorg.org> References: <1375858358-15070-1-git-send-email-wni@nvidia.com> <5201FC2C.4030908@roeck-us.net> <52020047.1080705@nvidia.com> <1375865105.562600640@f434.i.mail.ru> <520214C9.1010200@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <520214C9.1010200-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Wei Ni Cc: Alexander Shiyan , Guenter Roeck , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "lm-sensors-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Matthew Longnecker , "khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: linux-tegra@vger.kernel.org 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 >>>>>>> --- >>>>>>> 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.