Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756872AbbGQGgB (ORCPT ); Fri, 17 Jul 2015 02:36:01 -0400 Received: from mailgw02.mediatek.com ([210.61.82.184]:51716 "EHLO mailgw02.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751343AbbGQGf7 (ORCPT ); Fri, 17 Jul 2015 02:35:59 -0400 X-Listener-Flag: 11101 Message-ID: <1437114955.21534.15.camel@mtksdaap41> Subject: Re: [PATCH v5 2/3] pwm: add MediaTek display PWM driver support From: YH Huang To: Daniel Kurtz CC: Thierry Reding , Matthias Brugger , Mark Rutland , Rob Herring , Pawel Moll , , "open list:OPEN FIRMWARE AND..." , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , srv_heupstream , , "Sascha Hauer" , Yingjoe Chen , Date: Fri, 17 Jul 2015 14:35:55 +0800 In-Reply-To: References: <1436778294-47635-1-git-send-email-yh.huang@mediatek.com> <1436778294-47635-3-git-send-email-yh.huang@mediatek.com> <1436975995.15774.27.camel@mtksdaap41> <1437025108.18175.13.camel@mtksdaap41> <1437031079.8107.13.camel@mtksdaap41> <1437065050.11063.26.camel@mtksdaap41> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit MIME-Version: 1.0 X-MTK: N Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5299 Lines: 148 On Fri, 2015-07-17 at 01:18 +0800, Daniel Kurtz wrote: > On Fri, Jul 17, 2015 at 12:44 AM, YH Huang wrote: > > On Thu, 2015-07-16 at 23:21 +0800, Daniel Kurtz wrote: > >> On Thu, Jul 16, 2015 at 3:17 PM, YH Huang wrote: > >> > On Thu, 2015-07-16 at 14:54 +0800, Daniel Kurtz wrote: > >> >> On Thu, Jul 16, 2015 at 1:38 PM, YH Huang wrote: > >> >> > On Wed, 2015-07-15 at 23:59 +0800, YH Huang wrote: > >> >> >> On Mon, 2015-07-13 at 18:19 +0800, Daniel Kurtz wrote: > >> >> >> > On Mon, Jul 13, 2015 at 5:04 PM, YH Huang wrote: > >> >> >> > > +#ifdef CONFIG_PM_SLEEP > >> >> >> > > +static int mtk_disp_pwm_suspend(struct device *dev) > >> >> >> > > +{ > >> >> >> > > + struct mtk_disp_pwm *mdp = dev_get_drvdata(dev); > >> >> >> > > + > >> >> >> > > + clk_disable_unprepare(mdp->clk_main); > >> >> >> > > + clk_disable_unprepare(mdp->clk_mm); > >> >> >> > > + > >> >> >> > > + return 0; > >> >> >> > > +} > >> >> >> > > + > >> >> >> > > +static int mtk_disp_pwm_resume(struct device *dev) > >> >> >> > > +{ > >> >> >> > > + struct mtk_disp_pwm *mdp = dev_get_drvdata(dev); > >> >> >> > > + int ret; > >> >> >> > > + > >> >> >> > > + ret = clk_prepare_enable(mdp->clk_main); > >> >> >> > > + if (ret < 0) > >> >> >> > > + return ret; > >> >> >> > > + > >> >> >> > > + ret = clk_prepare_enable(mdp->clk_mm); > >> >> >> > > + if (ret < 0) { > >> >> >> > > + clk_disable_unprepare(mdp->clk_main); > >> >> >> > > + return ret; > >> >> >> > > + } > >> >> >> > > + > >> >> >> > > >> >> >> > Don't you also have to restore the PWM rate and frequency? > >> >> >> > > >> >> >> > Is it possible to save power at runtime by leaving mdp->clk_mm enabled > >> >> >> > (to generate the PWM signal), but disable mdp->clk_main (clock > >> >> >> > required to access PWM registers)? > >> >> >> > >> >> >> The pwm-backlight driver will restore the data. > >> >> >> > >> >> >> After I try to disable anyone of the two clocks at runtime, the > >> >> >> backlight doesn't work well(no immediate update or losing backlight). > >> >> >> So we need to keep both clock enabled. > >> > >> Do you mean you see backlight glitch because the clocks / backlight > >> were *already on* during the first config (Perhaps left on by the > >> bootloader)? > >> I don't know how to solve that problem. > >> Maybe Thierry does. > >> > >> In any case, this is a minor issue; we really shouldn't hold up > >> landing the driver to optimize when the clocks are enabled/disabled > >> :-). I'm happy enough with what you have in this patch. > > > > Sorry for my terrible expression. Let me try again. > > 1. We want to disable unnecessary clock at runtime. > > But, I get backlight glitch when I disable clk_main or clk_mm in > > mtk_disp_pwm_config(). So both clocks are necessary and we don't disable > > them at runtime. > > > > 2. Because pwm-backlight driver calls mtk_disp_pwm_config() before > > mtk_disp_pwm_enable(), we will lose the first config if clocks are > > enabled in mtk_disp_pwm_enable(). I prefer to enable clocks in probe > > function. Samsung did the same way in their pwm driver. > > I don't understand why you will "lose the first config if clocks are > enabled in mtk_disp_pwm_enable(). I don't believe registers will lose > their values just because you turn enable/disable clocks. > > Perhaps I wasn't clear with what I was proposing which is something like this: > > mtk_disp_pwm_config() > { > clk_enable(); > /* write registers */ > clk_disable(); > } > > mtk_disp_enable() > { > clk_enable(); > /* write enable bit */ > } > > mtk_disp_disable() > { > /* clear enable bit */ > clk_disable(); > } > > > In this way, if mtk_disp_pwm_config() is called when the pwm is > disabled, we will temporarily enable the clocks long enough to update > the register values. These values should take effect the next time > the PWM is enabled. We then disable the clocks and wait for the PWM > to be enabled. > > If mtk_disp_pwm_config() is called when the pwm is already enabled, we > will increment the enable count on the clocks, but then we decrement > it again immediately. I think there is something wrong about mdp->clk_mm(generate the PWM signal) and mdp->clk_main(access PWM registers). If we want to write the register, we should enable both clocks before. I try it in this way. mtk_disp_pwm_config() { clk_enable(mdp->clk_main); clk_enable(mdp->clk_mm); /* write registers */ clk_disable(mdp->clk_mm); clk_disable(mdp->clk_main); } with A: mtk_disp_enable() { clk_enable(mdp->clk_main); clk_enable(mdp->clk_mm); /* write enable bit */ clk_disable(mdp->clk_mm); } or B: mtk_disp_enable() { clk_enable(mdp->clk_main); clk_enable(mdp->clk_mm); /* write enable bit */ clk_disable(mdp->clk_main); } I both get backlight glitch with "A" or "B". So I think we should keep clocks enabled. Regards, YH Huang -- 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/