From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brownell Subject: Re: [PATCH 1/5] gpiolib: introduce set_debounce method Date: Fri, 21 May 2010 06:14:14 -0700 (PDT) Message-ID: <396934.73027.qm@web180307.mail.gq1.yahoo.com> References: <20100521111136.53dba6c9@lxorguk.ukuu.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from n12.bullet.mail.mud.yahoo.com ([209.191.125.209]:24124 "HELO n12.bullet.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751692Ab0EUNOP (ORCPT ); Fri, 21 May 2010 09:14:15 -0400 In-Reply-To: <20100521111136.53dba6c9@lxorguk.ukuu.org.uk> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: felipe.balbi@nokia.com, Alan Cox Cc: Mark Brown , Linux OMAP Mailing List , Linux Kernel Mailing List , Tony Lindgren , Andrew Morton --- On Fri, 5/21/10, Alan Cox wrote: > GPIO is almost always fairly tightly platform bound Not entirely. SOC based ones, yes. But GPIOs on expanders and ancillary chips have more variable capabilities, and many SOC-based boards have a bunch of those. > so features only > existing on certain ports is fine. The platform vendor will > have made > sure they relevant ports have suitable debounce > facilities. One of the earlier examples of why to want debouncing (in the original discussion, not this one) was for buttons (one signal per button press) and the hardware designers don't necessarily hook buttons up to only GPIOs with hardware debounce. So code to kick in debounce there needed to be sensitive to whether or not the capability was available ... and moreover, whether the debounce scale was adequate to compensate the contact chatter. When not, then software debounce was inescapable.