From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755361AbbBDNiz (ORCPT ); Wed, 4 Feb 2015 08:38:55 -0500 Received: from mail-la0-f44.google.com ([209.85.215.44]:34083 "EHLO mail-la0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751292AbbBDNix convert rfc822-to-8bit (ORCPT ); Wed, 4 Feb 2015 08:38:53 -0500 MIME-Version: 1.0 In-Reply-To: <20150129145636.GU21469@belle.intranet.vanheusden.com> References: <20150129145636.GU21469@belle.intranet.vanheusden.com> Date: Wed, 4 Feb 2015 14:38:52 +0100 Message-ID: Subject: Re: [3.18.3] poll() on gpio pins broken From: Linus Walleij To: folkert , Johan Hovold , =?UTF-8?Q?S=C3=B6ren_Brinkmann?= Cc: "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 29, 2015 at 3:56 PM, folkert wrote: > For timekeeping I wrote a program which waits for interrupts on > gpio-pins and then tells the local ntp daemon the clock offset. > I'm aware of the pps support in recent kernel but that does not work > (yet) on all platforms (eg cubieboard 1). > > This has worked for quite some time but no longer. > > Until at least kernel 3.12 I could do: > > // export gpio pin > // set direction to in > // set direction to rising > int fd = open("/sys.../value", O_RDONLY); > fdset[0].fd = fd; > fdset[0].events = POLLPRI; > fdset[0].revents = 0; > poll(fdset, 1, -1); > // at this point pin went high > > So: I would setup a gpio-pin using /sys-files, and then use poll() to > wait for the interrupt triggered by the level of the gpio pin going > high. > This worked fine on all raspberry pi's I tried, a nanos g20, a beagle > bone black and a cubieboard 1. > > Since kernel 3.18.3 (.4 as well) this no longer works: > > 1422542104.894908947] interrupt #2459, offset -0.105091s > 1422542104.895162937] interrupt #2460, offset -0.104837s > 1422542104.895408928] interrupt #2461, offset -0.104591s > 1422542104.895650919] interrupt #2462, offset -0.104349s > 1422542104.896293896] interrupt #2463, offset -0.103706s > ... > > As you can see suddenly the poll returns immediately. > > strace learns me: > poll([{fd=3, events=POLLPRI}], 1, -1) = 1 ([{fd=3, revents=POLLPRI|POLLERR}]) > > So apparently somewhere between 3.12 and 3.18 it is no longer > allowed/possible to do poll() on a gpio-pin value device. > > Am I right that something broke the abi? Or have I been doing it wrong > and did that became visible? > Please advise. Paging Johan and Sören into this discussion so they fully realize the horror of the GPIO sysfs ABI... Yours, Linus Walleij