Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755209Ab1CGDHz (ORCPT ); Sun, 6 Mar 2011 22:07:55 -0500 Received: from xes-mad.com ([216.165.139.218]:38292 "EHLO xes-mad.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754549Ab1CGDHy (ORCPT ); Sun, 6 Mar 2011 22:07:54 -0500 Subject: Re: [PATCH v5 2/4] gpiolib: Add ability to get GPIO direction From: Peter Tyser To: Grant Likely Cc: linux-kernel@vger.kernel.org, Alek Du , Samuel Ortiz , David Brownell , Eric Miao , Uwe =?ISO-8859-1?Q?Kleine-K=F6nig?= , Mark Brown , Joe Perches , Alan Cox In-Reply-To: <20110306073003.GA29325@angua.secretlab.ca> References: <1299022100-14564-1-git-send-email-ptyser@xes-inc.com> <1299022100-14564-2-git-send-email-ptyser@xes-inc.com> <20110306073003.GA29325@angua.secretlab.ca> Content-Type: text/plain; charset="UTF-8" Date: Sun, 06 Mar 2011 21:07:21 -0600 Message-ID: <1299467241.11719.145.camel@ptyser-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2099 Lines: 45 On Sun, 2011-03-06 at 00:30 -0700, Grant Likely wrote: > On Tue, Mar 01, 2011 at 05:28:18PM -0600, Peter Tyser wrote: > > Add a new get_direction() function to the gpio_chip structure. This is > > useful so that the direction of a GPIO can be determined when its > > initially exported. Previously, the direction defaulted to "unknown" > > regardless of the actual configuration of the GPIO. > > > > If a GPIO driver implements get_direction(), it is called in > > gpio_request() to set the initial direction of the GPIO accurately. > > I don't like this approach. It effectively creates two methods for > determining the direction of a gpio; either ask the driver, or read > the flags value. Currently, only gpio_request() actually uses the > first option, but it still leaves the ambiguity. > > Instead, the driver should be able to preload the direction flag at or > shortly after gpiochip_add() time. No need for a new callback hook > from what I can see. The callback hook was used because the gpio_desc[] structure was local to gpiolib.c. The code would have to be restructured a bit to allow drivers to set the flags themselves. I can do that if you'd prefer, but don't think it'd be all that much cleaner. Also, I thought it made sense to read the direction of the GPIO in gpio_request() because that's the point that the GPIO comes under the GPIO subsystem's control. Prior to that, there's a chance the direction could be changed by platform code, or another driver, etc, so reading the direction in gpiochip_add() may result in out-of-date directions. The reading of the direction could also be put in chip drivers' request() function. That would get rid of the callback and still ensure the direction is up-to-date. I think the current patch seems cleaner than the alternatives, but will change if you'd prefer. Best, Peter -- 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/