From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lothar =?UTF-8?B?V2HDn21hbm4=?= Date: Wed, 08 Nov 2017 07:34:07 +0000 Subject: Re: [PATCH 2/2] backlight: pwm_bl: add configurable delay between re-enabling PWM and switching back Message-Id: <20171108083407.1ae55f91@karo-electronics.de> List-Id: References: <1509022186-19636-1-git-send-email-LW@KARO-electronics.de> <1509022186-19636-4-git-send-email-LW@KARO-electronics.de> <20171027140307.x7mtgvy5py7l5nqf@rob-hp-laptop> <20171030103334.75ii247j6owrnrdb@dell> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Rob Herring Cc: Lee Jones , Bartlomiej Zolnierkiewicz , Daniel Thompson , Jacek Anaszewski , Jingoo Han , Mark Rutland , Pavel Machek , Richard Purdie , Thierry Reding , "devicetree@vger.kernel.org" , "linux-fbdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Linux LED Subsystem , Linux PWM List Hi, On Tue, 7 Nov 2017 18:46:18 -0600 Rob Herring wrote: > On Mon, Oct 30, 2017 at 5:33 AM, Lee Jones wrote: > > On Fri, 27 Oct 2017, Rob Herring wrote: > > > >> On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote: > >> > When switching the backlight on, the LCD may need some time to adjust > >> > to the configured PWM duty cycle. Add a configurable delay between > >> > configuring the PWM and enabling the backlight regulator to account > >> > for this. > >> > > >> > Signed-off-by: Lothar Waßmann > >> > --- > >> > .../bindings/leds/backlight/pwm-backlight.txt | 4 ++++ > >> > drivers/video/backlight/pwm_bl.c | 22 +++++++++++++++++++--- > >> > 2 files changed, 23 insertions(+), 3 deletions(-) > >> > > >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > >> > index 764db86..95594c3 100644 > >> > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > >> > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > >> > @@ -17,6 +17,10 @@ Optional properties: > >> > "pwms" property (see PWM binding[0]) > >> > - enable-gpios: contains a single GPIO specifier for the GPIO which enables > >> > and disables the backlight (see GPIO binding[1]) > >> > + - turn-on-delay-ms: delay in milliseconds between configuring the PWM > >> > + and switching PWM on. This may be required to eliminate > >> > + flicker when switching the PWM on after it has been > >> > + disabled. > >> > >> The subject talks about turning on the backlight regulator, but this > >> only talks about the PWM. > > > > From my understanding "switching PWM on" = enabling the regulator. > > > > I don't see any disparity here. Or am I missing something? > > The delay is from (re-)enabling the PWM (turning it on) to switching > backlight power on. That sounds like 2 different things to me. > The text should better read: + - turn-on-delay-ms: delay in milliseconds between configuring the PWM + and switching the backlight regulator on. This may be + required to eliminate flicker when switching the backlight + on after it had been disabled. Lothar Waßmann