Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932449Ab3HGIHq (ORCPT ); Wed, 7 Aug 2013 04:07:46 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:12214 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932428Ab3HGIHl (ORCPT ); Wed, 7 Aug 2013 04:07:41 -0400 X-PGP-Universal: processed; by hqnvupgp08.nvidia.com on Wed, 07 Aug 2013 01:05:59 -0700 Message-ID: <52020047.1080705@nvidia.com> Date: Wed, 7 Aug 2013 16:07:35 +0800 From: Wei Ni User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130623 Thunderbird/17.0.7 MIME-Version: 1.0 To: Guenter Roeck CC: Alexander Shiyan , "khali@linux-fr.org" , "swarren@wwwdotorg.org" , "linux-kernel@vger.kernel.org" , "lm-sensors@lm-sensors.org" , Matthew Longnecker , "linux-tegra@vger.kernel.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> <1375858358-15070-2-git-send-email-wni@nvidia.com> <1375860442.896960598@f427.i.mail.ru> <5201F811.9050602@nvidia.com> <5201FC2C.4030908@roeck-us.net> In-Reply-To: <5201FC2C.4030908@roeck-us.net> 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: 2258 Lines: 63 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. 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 > -- 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/