From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ezequiel Garcia Subject: Re: [PATCH v1 3/3] ARM: dts: am335x-bone: add support for beaglebone LCD4 cape Date: Wed, 25 Jun 2014 11:59:10 -0300 Message-ID: <20140625145910.GC743@arch.cereza> References: <1403612666-31197-1-git-send-email-pekon@ti.com> <1403612666-31197-4-git-send-email-pekon@ti.com> <20140624150336.GA10041@arch.cereza> <20980858CB6D3A4BAE95CA194937D5E73EAF7327@DBDE04.ent.ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-yh0-f47.google.com ([209.85.213.47]:43366 "EHLO mail-yh0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756454AbaFYPAD (ORCPT ); Wed, 25 Jun 2014 11:00:03 -0400 Received: by mail-yh0-f47.google.com with SMTP id v1so1219774yhn.6 for ; Wed, 25 Jun 2014 08:00:02 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20980858CB6D3A4BAE95CA194937D5E73EAF7327@DBDE04.ent.ti.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: "Gupta, Pekon" Cc: Tony Lindgren , Jason Kridner , Robert Nelson , linux-omap , linux-mtd , Guido =?iso-8859-1?Q?Mart=EDnez?= On 25 Jun 04:38 AM, Gupta, Pekon wrote: > >From: Ezequiel Garcia > >>On 24 Jun 05:54 PM, Pekon Gupta wrote: > >> This patch adds support for LCD4 cape as advertised on > >> http://elinux.org/CircuitCo:BeagleBone_LCD4 > >> > >> This cape has: > >> * 480x272 TFT-LCD panel > >> - LCD panel datasheet and timing information are sourced from [1] > >> - LCD backlight is connected to 'EHRPWM1A' on cape board, but its used for > >> enabling backlight power-supply. So 'gpio-backlight' driver is used instead > >> of 'pwm-backlight' driver (Kconfig: BACKLIGHT_GPIO=y). > >> > > > >I'm confused about this, can you clarify why you are not using pwm-backlight? > > > > As per the schematics of this LCD4 cape board, "EHRPWM1A" pin controls > enabling/disabling of the power to backlight LED. It does not control the > voltage levels (brightness levels) of the LED. Thus it wasn't making sense > to use pwm-backlight driver which more suitable in cases where you have > multiple levels of brightness. > Here, you have only 2 levels "backlight=off | on", so I used gpio-backlight driver. > Though you can use pwm-backlight driver also, but the backlight turns ON > only when you set the /sys/class/backlight//brighteness > to maximum level (as set in DT). > Hm, I didn't know that. Thanks for this information. -- Ezequiel Garcia, VanguardiaSur www.vanguardiasur.com.ar