From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1034651AbcIWOCT (ORCPT ); Fri, 23 Sep 2016 10:02:19 -0400 Received: from mail-io0-f196.google.com ([209.85.223.196]:36200 "EHLO mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1034358AbcIWOCO (ORCPT ); Fri, 23 Sep 2016 10:02:14 -0400 MIME-Version: 1.0 In-Reply-To: <1472147411-30424-2-git-send-email-oliver@schinagl.nl> References: <1472147411-30424-2-git-send-email-oliver@schinagl.nl> From: Jonathan Liu Date: Sat, 24 Sep 2016 00:02:13 +1000 Message-ID: Subject: Re: [1/2] pwm: sunxi: allow the pwm to finish its pulse before disable To: oliver@schinagl.nl Cc: Alexandre Belloni , Thierry Reding , Maxime Ripard , Chen-Yu Tsai , linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26 August 2016 at 03:50, wrote: > When we inform the PWM block to stop toggeling the output, we may end up > in a state where the output is not what we would expect (e.g. not the > low-pulse) but whatever the output was at when the clock got disabled. > > To counter this we have to wait for maximally the time of one whole > period to ensure the pwm hardware was able to finish. Since we already > told the PWM hardware to disable it self, it will not continue toggling > but merly finish its current pulse. > > If a whole period is considered to much, it may be contemplated to use a > half period + a little bit to ensure we get passed the transition. > > Signed-off-by: Olliver Schinagl > --- > drivers/pwm/pwm-sun4i.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c > index 03a99a5..5e97c8a 100644 > --- a/drivers/pwm/pwm-sun4i.c > +++ b/drivers/pwm/pwm-sun4i.c > @@ -8,6 +8,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -245,6 +246,16 @@ static void sun4i_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) > spin_lock(&sun4i_pwm->ctrl_lock); > val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG); > val &= ~BIT_CH(PWM_EN, pwm->hwpwm); > + sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG); > + spin_unlock(&sun4i_pwm->ctrl_lock); > + > + /* Allow for the PWM hardware to finish its last toggle. The pulse > + * may have just started and thus we should wait a full period. > + */ > + ndelay(pwm_get_period(pwm)); > + > + spin_lock(&sun4i_pwm->ctrl_lock); > + val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG); > val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm); > sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG); > spin_unlock(&sun4i_pwm->ctrl_lock); I had some issues where setting the brightness for pwm-backlight to 0 was not turning off the backlight sometimes. This patch fixes the issue for me. Thanks. Tested-by: Jonathan Liu