From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A69A8C169C4 for ; Wed, 6 Feb 2019 08:49:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 74949217F9 for ; Wed, 6 Feb 2019 08:49:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728553AbfBFItH (ORCPT ); Wed, 6 Feb 2019 03:49:07 -0500 Received: from mx07-00178001.pphosted.com ([62.209.51.94]:41189 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727249AbfBFItD (ORCPT ); Wed, 6 Feb 2019 03:49:03 -0500 Received: from pps.filterd (m0046037.ppops.net [127.0.0.1]) by mx07-00178001.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x168fNlG019552; Wed, 6 Feb 2019 09:48:49 +0100 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx07-00178001.pphosted.com with ESMTP id 2qfv9n8100-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Wed, 06 Feb 2019 09:48:49 +0100 Received: from zeta.dmz-eu.st.com (zeta.dmz-eu.st.com [164.129.230.9]) by beta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 4E6C7231; Wed, 6 Feb 2019 08:42:50 +0000 (GMT) Received: from Webmail-eu.st.com (sfhdag5node3.st.com [10.75.127.15]) by zeta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 0E711169B; Wed, 6 Feb 2019 08:42:50 +0000 (GMT) Received: from [10.48.0.167] (10.75.127.47) by SFHDAG5NODE3.st.com (10.75.127.15) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 6 Feb 2019 09:42:48 +0100 Subject: Re: [PATCH 2/4] pwm: stm32-lp: Add power management support To: Thierry Reding , =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= CC: , , , , , , , , , , , , Tomasz Duszynski References: <1549370429-19116-1-git-send-email-fabrice.gasnier@st.com> <1549370429-19116-3-git-send-email-fabrice.gasnier@st.com> <20190205204732.zrbhgyxnvjbwfyw4@pengutronix.de> <20190205222522.GB1372@mithrandir> From: Fabrice Gasnier Message-ID: <6584a59b-657d-adc9-fab2-eb1a9baba05d@st.com> Date: Wed, 6 Feb 2019 09:42:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190205222522.GB1372@mithrandir> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.75.127.47] X-ClientProxiedBy: SFHDAG5NODE1.st.com (10.75.127.13) To SFHDAG5NODE3.st.com (10.75.127.15) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-02-06_06:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/5/19 11:25 PM, Thierry Reding wrote: > On Tue, Feb 05, 2019 at 09:47:32PM +0100, Uwe Kleine-König wrote: >> Hello, >> >> On Tue, Feb 05, 2019 at 01:40:27PM +0100, Fabrice Gasnier wrote: >>> Add suspend/resume PM sleep ops. When going to low power, disable >>> active PWM channel. Active PWM channel is resumed, by calling >>> pwm_apply_state(). This is inspired by Thierry's comment in [1]. >>> Don't touch inactive channels, as it may be used by other LPTimer MFD >>> child driver. >>> [1]https://lkml.org/lkml/2017/12/5/175 >>> >>> Signed-off-by: Fabrice Gasnier >>> --- >>> drivers/pwm/pwm-stm32-lp.c | 38 ++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 38 insertions(+) >>> >>> diff --git a/drivers/pwm/pwm-stm32-lp.c b/drivers/pwm/pwm-stm32-lp.c >>> index 0059b24c..0c40d48 100644 >>> --- a/drivers/pwm/pwm-stm32-lp.c >>> +++ b/drivers/pwm/pwm-stm32-lp.c >>> @@ -13,6 +13,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> >>> @@ -20,6 +21,8 @@ struct stm32_pwm_lp { >>> struct pwm_chip chip; >>> struct clk *clk; >>> struct regmap *regmap; >>> + struct pwm_state suspend; >>> + bool suspended; >>> }; >>> >>> static inline struct stm32_pwm_lp *to_stm32_pwm_lp(struct pwm_chip *chip) >>> @@ -223,6 +226,40 @@ static int stm32_pwm_lp_remove(struct platform_device *pdev) >>> return pwmchip_remove(&priv->chip); >>> } >>> >>> +#ifdef CONFIG_PM_SLEEP >>> +static int stm32_pwm_lp_suspend(struct device *dev) >>> +{ >>> + struct stm32_pwm_lp *priv = dev_get_drvdata(dev); >>> + >>> + pwm_get_state(&priv->chip.pwms[0], &priv->suspend); >>> + priv->suspended = priv->suspend.enabled; >>> + >>> + /* safe to call pwm_disable() for already disabled pwm */ >>> + pwm_disable(&priv->chip.pwms[0]); >>> + >>> + return pinctrl_pm_select_sleep_state(dev); >> >> IMHO a PWM should not stop if the PWM user didn't call pwm_disable() (or >> pwm_apply_state() with .enabled = false). >> >> I don't understand all the PM details, but I think there is no defined >> order in which devices are signalled to suspend. If so the PWM might be >> stopped before its consumer. Then the PWM changes state without the >> consumer being aware of that. >> >> I understand Thierry's position in the link you provided in the commit >> log consistant with my position here. > > Agreed, we should let users of the PWM take care of resuming the PWM in > the state and at the point in time that they require so. PWM users will > also likely do a pwm_disable() during their suspend implementation, so > doing this again in a PWM ->suspend() is not necessary, even if perhaps > harmless. > > So this leaves only the pinctrl_pm_select_sleep_state() call. That seems > fine, but I'm not sure that that's currently guaranteed to work. I think > we may need to implement device link support in the PWM framework to > guarantee the proper suspend/resume sequencing. Otherwise you may end up > in a situation where the PWM is actually suspended before the user and > glitch the pins before the user has a chance to disable the PWM. Hi Uwe, Thierry, I agree with both of you on the analysis. > > I think it'd be fine to merge the driver change here first before we add > device link support if this works for you. Just mentioning the issue > here in case you ever run into it. If you agree with the current approach, I can send a V2 with Tomasz's suggestion to remove the ifdefs and use __maybe_unused instead. Thanks for reviewing, Best Regards, Fabrice > > Thierry >