Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753266Ab1CGGw7 (ORCPT ); Mon, 7 Mar 2011 01:52:59 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:48272 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751035Ab1CGGw5 (ORCPT ); Mon, 7 Mar 2011 01:52:57 -0500 Date: Sun, 6 Mar 2011 23:52:53 -0700 From: Grant Likely To: Peter Tyser 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 , Lars-Peter Clausen , Alexander Stein , Ryan Mallon Subject: Re: [PATCH v5 1/4] gpiolib: Add "unknown" direction support Message-ID: <20110307065253.GB29999@angua.secretlab.ca> References: <1299022100-14564-1-git-send-email-ptyser@xes-inc.com> <20110306072505.GC7467@angua.secretlab.ca> <1299465785.11719.114.camel@ptyser-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1299465785.11719.114.camel@ptyser-laptop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1656 Lines: 31 On Sun, Mar 06, 2011 at 08:43:05PM -0600, Peter Tyser wrote: > > The thing about gpios is that how they are used is entirely dependant > > on what they are wired up to. There is no avoiding the fact that you > > *absolutely* must understand the usage model before even considering > > fiddling with a gpio (ignoring the "I wonder what this knob does" > > use-case such as when reverse engineer a board). So, while it is nice > > to have an 'unknown' state for sysfs to report, it is certainly not > > required. The model still remains that the pin direction must be set > > before (or at the same time as) reading/writing the pin. > > As is, even if someone knows about the GPIO wiring on their board, they > have to know Linux has a "rule" that "before I can use a GPIO, I have to > explicitly set its direction, even if the current reported direction is > what I want". A number of our customers have tried to use a GPIO which > states its an 'input' as an input after exporting it, which is > completely logical. But it doesn't work, because its not really an > input... Why not set the direction accurately as 'unknown' so users > intuitively know they have to set the direction before using it? You > also mention that it would be a nice feature above, so why not include > it? I don't like what it does to the implementation, and I'd rather make drivers provide accurate data at the outset. g. -- 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/