From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932549AbcDVPo2 (ORCPT ); Fri, 22 Apr 2016 11:44:28 -0400 Received: from 7of9.schinagl.nl ([88.159.158.68]:54852 "EHLO 7of9.schinagl.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932275AbcDVPoY (ORCPT ); Fri, 22 Apr 2016 11:44:24 -0400 User-Agent: K-9 Mail for Android In-Reply-To: References: <1461051650-18824-1-git-send-email-oliver@schinagl.nl> <1461051650-18824-6-git-send-email-oliver@schinagl.nl> <20160421150750.GA3116@rob-hp-laptop> <571A1B60.3020804@schinagl.nl> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Subject: Re: [PATCH 5/6] leds: pca963x: Inform the output that it is inverted From: Olliver Schinagl Date: Fri, 22 Apr 2016 17:44:09 +0200 To: Rob Herring CC: Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Richard Purdie , Jacek Anaszewski , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Linux LED Subsystem Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On April 22, 2016 3:09:35 PM CEST, Rob Herring wrote: >On Fri, Apr 22, 2016 at 7:38 AM, Olliver Schinagl >wrote: >> Hey Rob, >> >> On 21-04-16 17:07, Rob Herring wrote: >>> >>> On Tue, Apr 19, 2016 at 09:40:49AM +0200, Olliver Schinagl wrote: >>>> >>>> When leds are connected in a totem-pole configuration, they can be >>>> connected either in a active-high, or active-low manor. The driver >>>> currently always assumes active-high. This patch adds the >>>> 'nxp,inverted-out' boolean property to tell the driver that the >leds >>>> are driven active-low, or rather, that the behavior is inverted to >what >>>> is normally expected. >>> >>> How do I know what is normally expected? >> >> fair point, and in fact, you don't. The text is bad here. > >The problem is not so much the text here, but the property is also >meaningless without some explanation. > Well the datasheet states only that it will invert the output. So would it make sense to just state the same here? >>> >>> >>>> Signed-off-by: Olliver Schinagl >>>> --- >>>> Documentation/devicetree/bindings/leds/pca963x.txt | 1 + >>>> drivers/leds/leds-pca963x.c | 20 >>>> +++++++++++++------- >>>> include/linux/platform_data/leds-pca963x.h | 1 + >>>> 3 files changed, 15 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/Documentation/devicetree/bindings/leds/pca963x.txt >>>> b/Documentation/devicetree/bindings/leds/pca963x.txt >>>> index dafbe99..7b23725 100644 >>>> --- a/Documentation/devicetree/bindings/leds/pca963x.txt >>>> +++ b/Documentation/devicetree/bindings/leds/pca963x.txt >>>> @@ -6,6 +6,7 @@ Required properties: >>>> Optional properties: >>>> - nxp,totem-pole : use totem pole (push-pull) instead of >open-drain >>>> (pca9632 defaults >>>> to open-drain, newer chips to totem pole) >>>> + nxp,inverted-out: the connected leds are active-low, default to >>>> active-high >>> >>> Just state what mode you want: nxp,active-low >> >> But that's not what happens, which is why my text is bad :) It >depends on >> how the board is wired and if it is push-pull or open-drain. Though >this >> goes beyond my electronics knowledge. So I'll reduce the text to say >exactly >> what we mean, inverted output (or not). >> >> Unless you can explain that it would be unrelated and it is actually >> active-high/low. I'll be more than happy to oblige. > >I'm not familiar with this chip, but googling for "active low LED >circuit" can give you lots of examples. To put it simply, you are >defining whether the control/switch is on the cathode or anode side of >the LED. Open-drain vs. push-pull is also related to how the circuit >is done, but is probably an independent property. I'd think the only >reason you would use open-drain here is if you wanted to control the >LED from 2 different signals. Whether you wanted the controls to >function as OR or AND logic to turn on would determine what the active >state needs to be. I was thinking that the output behaves differently depending whether it is configured as push-pull or open-drain. So to summarize, does the output always go into active-low mode, or does it depend on other parameters as well? Olliver > >Rob -- Sent from my Android device with K-9 Mail. Please excuse my brevity.