From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753710Ab1KUWuA (ORCPT ); Mon, 21 Nov 2011 17:50:00 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:49593 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750904Ab1KUWt7 (ORCPT ); Mon, 21 Nov 2011 17:49:59 -0500 Message-ID: <4ECAD613.3030605@solonet.org.ua> Date: Tue, 22 Nov 2011 00:52:03 +0200 From: Denis Kuzmenko User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20111110 Icedove/3.0.11 MIME-Version: 1.0 To: Stephen Warren CC: "linux-kernel@vger.kernel.org" , Grant Likely , Linus Walleij , Richard Purdie , Wolfram Sang Subject: Re: [PATCH] s3c/s3c24xx: arm: leds: Make s3c24xx LEDS driver use gpiolib References: <4EC572E1.1020209@solonet.org.ua> <74CDBE0F657A3D45AFBB94109FB122FF1740D74E87@HQMAIL01.nvidia.com> <4EC6C785.5010801@solonet.org.ua> <4EC6D1D5.9060808@solonet.org.ua> <74CDBE0F657A3D45AFBB94109FB122FF1740D74FAD@HQMAIL01.nvidia.com> <4EC6DD8F.9070904@solonet.org.ua> <74CDBE0F657A3D45AFBB94109FB122FF1740D74FE6@HQMAIL01.nvidia.com> <4EC6E75E.2080200@solonet.org.ua> <74CDBE0F657A3D45AFBB94109FB122FF174F08C135@HQMAIL01.nvidia.com> <4ECAA894.4050500@solonet.org.ua> <74CDBE0F657A3D45AFBB94109FB122FF174F08C246@HQMAIL01.nvidia.com> In-Reply-To: <74CDBE0F657A3D45AFBB94109FB122FF174F08C246@HQMAIL01.nvidia.com> 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 On 11/22/2011 12:03 AM, Stephen Warren wrote: > Denis Kuzmenko wrote at Monday, November 21, 2011 12:38 PM: >> On 11/21/2011 08:07 PM, Stephen Warren wrote: >>> Denis Kuzmenko wrote at Friday, November 18, 2011 4:17 PM: >>>> On 11/19/2011 12:44 AM, Stephen Warren wrote: > ... >>>>> OK, I see the need for a pull of some kind (although aren't there meant >>>>> to be ESD protection diodes for this purpose; relying on what are probably >>>>> pretty weak pullup/down resistors doesn't seem like it will provide much >>>>> protection at all). >>>> >>>> I don't mean pull as any kind of good protection. But it's much better >>>> to have it than not. >>> >>> Hmm. I'm not entirely convinced. If the board already has a pull-up/down, >>> it seems like it won't really make much difference to ESD, and you can't >>> make any assumptions in the core driver about whether such an external >>> resistor is already present. In fact, adding another pull resistor inside >>> the SoC in parallel will reduce the overall resistance, and increase wasted >>> power. >>> >> >> I don't think it's a real protection. It's rather "mistake-proofing" >> (Poka-Yoke). >> You are right, I didn't considered additional pulls (however I can't >> imagine tristate LED usage with additional external pull) and power >> consumptions. >> I was just wondering, why was pull needed in previous implementation. >> Additional ESD protection was the only thing I could imagine. I don't >> think it's needed there and I'm OK to remove pull-related code. >> So I'll remove it, test and send patch V3? > > I don't see any pulls being configured in the original code at all, > unless some of the s3c2410_* function have unexpected side-effect. The > only related thing is in probe: > > /* no point in having a pull-up if we are always driving */ > > if (pdata->flags & S3C24XX_LEDF_TRISTATE) { > .. > } else { > s3c2410_gpio_pullup(pdata->gpio, 0); > > which I assume disables an pull in the case where the pin is always driven. > > So, yes, I'd say submit v3 without any pull manipulation at all. > Actually, "s3c2410_gpio_pullup(pdata->gpio, 0);" enables pull in the same way I've done that. Here is it's code: /* gpiolib wrappers until these are totally eliminated */ void s3c2410_gpio_pullup(unsigned int pin, unsigned int to) { int ret; WARN_ON(to); /* should be none of these left */ if (!to) { /* if pull is enabled, try first with up, and if that * fails, try using down */ ret = s3c_gpio_setpull(pin, S3C_GPIO_PULL_UP); if (ret) s3c_gpio_setpull(pin, S3C_GPIO_PULL_DOWN); } else { s3c_gpio_setpull(pin, S3C_GPIO_PULL_NONE); } } So pull is enabled in same "random" way as I did but for *opposite* state of S3C24XX_LEDF_TRISTATE flag. And again: >> I was just wondering, why was pull needed in previous implementation. >> Additional ESD protection was the only thing I could imagine. I don't >> think it's needed there and I'm OK to remove pull-related code. >> So I'll remove it, test and send patch V3? -- Best regards, Denis Kuzmenko.