Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754110AbdDKIWq (ORCPT ); Tue, 11 Apr 2017 04:22:46 -0400 Received: from esa4.microchip.iphmx.com ([68.232.154.123]:24429 "EHLO esa4.microchip.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754059AbdDKIWn (ORCPT ); Tue, 11 Apr 2017 04:22:43 -0400 X-IronPort-AV: E=Sophos;i="5.37,184,1488870000"; d="scan'208";a="1280885" Subject: Re: [PATCH] drivers: pwm: pwm-atmel: implement suspend/resume functions To: Boris Brezillon References: <1491834020-3194-1-git-send-email-claudiu.beznea@microchip.com> <20170410163558.494cf9be@bbrezillon> CC: , , , , , From: m18063 Message-ID: Date: Tue, 11 Apr 2017 11:22:39 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170410163558.494cf9be@bbrezillon> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3636 Lines: 107 Hi Boris, On 10.04.2017 17:35, Boris Brezillon wrote: > On Mon, 10 Apr 2017 17:20:20 +0300 > Claudiu Beznea wrote: > >> Implement suspend and resume power management specific >> function to allow PWM controller to correctly suspend >> and resume. >> >> Signed-off-by: Claudiu Beznea >> --- >> drivers/pwm/pwm-atmel.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 81 insertions(+) >> >> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c >> index 530d7dc..75177c6 100644 >> --- a/drivers/pwm/pwm-atmel.c >> +++ b/drivers/pwm/pwm-atmel.c >> @@ -58,6 +58,8 @@ >> #define PWM_MAX_PRD 0xFFFF >> #define PRD_MAX_PRES 10 >> >> +#define PWM_MAX_CH_NUM (4) >> + >> struct atmel_pwm_registers { >> u8 period; >> u8 period_upd; >> @@ -65,11 +67,18 @@ struct atmel_pwm_registers { >> u8 duty_upd; >> }; >> >> +struct atmel_pwm_pm_ctx { >> + u32 cmr; >> + u32 cdty; >> + u32 cprd; >> +}; >> + >> struct atmel_pwm_chip { >> struct pwm_chip chip; >> struct clk *clk; >> void __iomem *base; >> const struct atmel_pwm_registers *regs; >> + struct atmel_pwm_pm_ctx ctx[PWM_MAX_CH_NUM]; > > Hm, I'm pretty sure you can rely on the current PWM state and call > atmel_pwm_apply() at resume time instead of doing that. See what I did > here [1]. I agree with the approach you propose but the thing is the atmel_pwm_apply() take care of both, current PWM state and the new state received as argument in order to change only duty factor without disabling the PWM channel (if channel is enabled) and then returns. Changing PWM duty and period and polarity in the same step without disabling + enabling the PWM channel (with atomic approach) may lead to intermediary unwanted output waveforms (the IP doesn't support this for ordinary PWM channels). To take advantage of atmel_pwm_apply() (in the formit is today) in resume() hook might need to first call it to disable channel and then to enable it. Or atmel_pwm_apply() should be changed to also disable + enable the channel when user changes the duty factor at runtime. > > Thierry, maybe it's time to start thinking about a generic solution to > save/restore PWM states. > >> >> unsigned int updated_pwms; >> /* ISR is cleared when read, ensure only one thread does that */ >> @@ -333,6 +342,77 @@ atmel_pwm_get_driver_data(struct platform_device *pdev) >> return (struct atmel_pwm_registers *)id->driver_data; >> } >> >> +#ifdef CONFIG_PM_SLEEP >> +static int atmel_pwm_suspend(struct device *dev) >> +{ >> + struct atmel_pwm_chip *atmel_pwm = dev_get_drvdata(dev); >> + struct pwm_device *pwm = atmel_pwm->chip.pwms; >> + int i; >> + bool disable_clk = false; >> + >> + for (i = 0; i < atmel_pwm->chip.npwm; i++, pwm++) { >> + if (!pwm_is_enabled(pwm)) >> + continue; >> + >> + disable_clk = true; >> + atmel_pwm->ctx[i].cdty = >> + atmel_pwm_ch_readl(atmel_pwm, i, >> + atmel_pwm->regs->duty); >> + atmel_pwm->ctx[i].cprd = >> + atmel_pwm_ch_readl(atmel_pwm, i, >> + atmel_pwm->regs->period); >> + atmel_pwm->ctx[i].cmr = >> + atmel_pwm_ch_readl(atmel_pwm, i, PWM_CMR); >> + >> + atmel_pwm_disable(&atmel_pwm->chip, pwm, false); >> + } >> + >> + if (disable_clk) >> + clk_disable(atmel_pwm->clk); > > I'm not so sure we want to disable the PWM and the PWM chip clk when > entering suspend. What if the PWM is driving a critical device (like a > regulator) that has to stay enabled in suspend? > Shouldn't we delegate this responsibility to the PWM user? It is a good point. > > [1]http://patchwork.ozlabs.org/patch/734306/ >