Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752995AbdF2NIA (ORCPT ); Thu, 29 Jun 2017 09:08:00 -0400 Received: from mail-wm0-f44.google.com ([74.125.82.44]:37590 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752748AbdF2NHw (ORCPT ); Thu, 29 Jun 2017 09:07:52 -0400 Subject: Re: [PATCH 1/2] dt-bindings: pwm-backlight: Add pwm-delay-us property To: Enric Balletbo Serra , Pavel Machek Cc: Enric Balletbo i Serra , Thierry Reding , Lee Jones , 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 References: <20170628111632.22582-1-enric.balletbo@collabora.com> <20170628133004.GA3507@localhost> From: Daniel Thompson Message-ID: Date: Thu, 29 Jun 2017 14:07:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3461 Lines: 79 On 28/06/17 15:15, Enric Balletbo Serra wrote: > 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 think so. Like you I can't actually point at any asymmetric power sequence diagrams but there are a controller devices with power sequencing registers that support asymmetry. I'm inclined to take that as a hint... >> 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