Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756951Ab3HGQGf (ORCPT ); Wed, 7 Aug 2013 12:06:35 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:37811 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753797Ab3HGQGe (ORCPT ); Wed, 7 Aug 2013 12:06:34 -0400 Message-ID: <52027086.1090608@wwwdotorg.org> Date: Wed, 07 Aug 2013 10:06:30 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Wei Ni CC: Alexander Shiyan , Guenter Roeck , "linux-kernel@vger.kernel.org" , "lm-sensors@lm-sensors.org" , "linux-tegra@vger.kernel.org" , Matthew Longnecker , "khali@linux-fr.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 1/2] hwmon: (lm90) Add power control 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> In-Reply-To: <520214C9.1010200@nvidia.com> X-Enigmail-Version: 1.4.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2936 Lines: 71 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/