Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754441Ab3I0Ngq (ORCPT ); Fri, 27 Sep 2013 09:36:46 -0400 Received: from smtp.newsguy.com ([74.209.136.69]:54906 "EHLO smtp.newsguy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754022Ab3I0NgL (ORCPT ); Fri, 27 Sep 2013 09:36:11 -0400 Message-ID: <524589A3.50700@newsguy.com> Date: Fri, 27 Sep 2013 06:35:31 -0700 From: Mike Dunn User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130623 Thunderbird/17.0.6 MIME-Version: 1.0 To: Thierry Reding CC: Tomi Valkeinen , Richard Purdie , Jingoo Han , Jean-Christophe Plagniol-Villard , Grant Likely , Rob Herring , linux-pwm@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, Robert Jarzmik , Marek Vasut Subject: Re: [PATCH] pwm-backlight: add support for device tree gpio control References: <1378236372-15711-1-git-send-email-mikedunn@newsguy.com> <20130910172130.GC22111@ulmo> <523056A6.5060000@newsguy.com> <524408BE.40402@ti.com> <20130926120248.GB1680@ulmo> <524427E5.50403@ti.com> <20130926125020.GA2141@ulmo> In-Reply-To: <20130926125020.GA2141@ulmo> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3138 Lines: 64 On 09/26/2013 05:50 AM, Thierry Reding wrote: > On Thu, Sep 26, 2013 at 03:26:13PM +0300, Tomi Valkeinen wrote: >> On 26/09/13 15:02, Thierry Reding wrote: >>> On Thu, Sep 26, 2013 at 01:13:18PM +0300, Tomi Valkeinen wrote: >>>> On 11/09/13 14:40, Mike Dunn wrote: >>>>> On 09/10/2013 10:21 AM, Thierry Reding wrote: >>>> >>>>>> Do you have a real setup that actually needs multiple GPIOs? Usually >>>>>> such a setup requires some kind of timing or other additional constraint >>>>>> which can't be represented by this simple binding. >>>>>> >>>>>> Looking at the Palm Treo code it seems like the reason why multiple >>>>>> GPIOs are needed is because one is to enable the backlight, while the >>>>>> other is in fact used to enable the LCD panel. >>>>> >>>>> >>>>> There are actually four GPIOs involved! (There is an embarrasingly horrible >>>>> hack in arch/arm/mach-pxa/palmtreo.c that handles the others.) One is almost >>>>> certainly simply backlight power. The other three are probably LCD related. >>>> >>>> When you say "power", do you mean the gpio enables a regulator to feed >>>> power to the backlight? If so, wouldn't that be a regulator, not gpio, >>>> from the bl driver's point of view? >>>> >>>> Generally speaking, this same problem appears in many places, but for >>>> some reason especially in display. I'm a bit hesitant in adding "free >>>> form" gpio/regulator support for drivers, as, as Thierry pointed out, >>>> there are often timing requirements, or sometimes the gpios are >>>> inverted, or sometimes the gpio is, in fact, a reset gpio, where you'll >>>> assert the gpio for a short moment only. >>> >>> I sent out another series a few days ago that somewhat obsoletes this >>> patch. What it does is basically add a single enable GPIO that can be >>> used to turn the backlight on and off. In a separate patch, support is >>> added for a power regulator. The combination of both should be able to >>> cover the majority of use-cases. >> >> But Mike's case required 4 GPIOs? Or can that be reduced to one gpio and >> one regulator? > > Well, at least for the backlight it only seemed to involve a single > GPIO. The other three were probably related to LCD and therefore not > really suitable for a backlight driver. Traditionally it has been that > the backlight driver handled these things as well (via the callbacks > installed by board setup code). While really they should be handled by a > separate driver (for the LCD). Yes, this is currently my best guess. This is reverse-engineered and unfortunately I'm not yet able to accurately describe my particular use-case. Probably as wacky as anything you can imagine, Thierry :) The gpio and regulator patches will probably suffice. Thierry, can you please point me to those patches? I don't see them in your gitorious tree. If they were posted to linux-pwm, I missed them; sorry. Thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/