Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752026AbdF1OP1 (ORCPT ); Wed, 28 Jun 2017 10:15:27 -0400 Received: from mail-it0-f65.google.com ([209.85.214.65]:34807 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751888AbdF1OPZ (ORCPT ); Wed, 28 Jun 2017 10:15:25 -0400 MIME-Version: 1.0 In-Reply-To: <20170628133004.GA3507@localhost> References: <20170628111632.22582-1-enric.balletbo@collabora.com> <20170628133004.GA3507@localhost> From: Enric Balletbo Serra Date: Wed, 28 Jun 2017 16:15:22 +0200 Message-ID: Subject: Re: [PATCH 1/2] dt-bindings: pwm-backlight: Add pwm-delay-us property To: Pavel Machek Cc: Enric Balletbo i Serra , Thierry Reding , Lee Jones , Daniel Thompson , Jingoo Han , Bartlomiej Zolnierkiewicz , Rob Herring , Richard Purdie , Jacek Anaszewski , linux-pwm@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-kernel , Guenter Roeck , huang lin Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3083 Lines: 72 Hi Daniel, Pavel, 2017-06-28 15:30 GMT+02:00 Pavel Machek : > On Wed 2017-06-28 13:16:31, Enric Balletbo i Serra wrote: >> From: huang lin >> >> Add a pwm-delay-us property to specify the delay between setting an >> initial (non-zero) PWM value and enabling the backlight, and also the >> delay between disabling the backlight and setting PWM value to 0. > > > >> Signed-off-by: huang lin >> Signed-off-by: Enric Balletbo i Serra >> --- >> Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> index 764db86..f75b08f 100644 >> --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> @@ -17,6 +17,9 @@ 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]) >> + - pwm-delay-us: delay between setting an initial (non-zero) PWM value and >> + enabling the backlight, and also the delay between disabling >> + the backlight and setting PWM value to 0. >> > >> If is safe to assume power-on delay and power-off delay will be the same? >> >> I've only took a quick look but several backlight controllers support asymetric power-on/off sequences.. Daniel, right the ones I checked are symmetric but asymmetric timings are possible I guess, so I think now that specify the two delays is more accurate, maybe the binding should be something like this? pwm-delay-us = ; > I understood it as "you set PWM and it takes a while for display to > light up" > but that's not correct. Changelog from second patch makes it > clear. Please > clarify it here, too. Pavel, oh, your dude is interesting ... That's the idea, the sequence is: Power on, you set the PWM signal, wait a bit and set the LED_EN signal. Power off, you clear the LED_EN signal, wait a bit and stop the PWM signal. Note that the patch inverts the sequence, before this patch first you set LED_EN signal and then the PWM signal I assumed that the sequence was wrong but maybe I'm mistaken and there are some panels that follow the original sequence. On the few panels I checked the power on/off sequence is how I described above, i.e. see [1] p. 17, the sequence is first PWM and then LED_EN. I'll take a look at other panel datasheets, or if you know one, could you provide me the datasheet? Thanks, [1] http://www.jxlcd.com/Upload/PicFiles/N116BGE-L41.pdf > > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html