From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753752AbaFWXf0 (ORCPT ); Mon, 23 Jun 2014 19:35:26 -0400 Received: from mail-pd0-f174.google.com ([209.85.192.174]:59643 "EHLO mail-pd0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753200AbaFWXfY (ORCPT ); Mon, 23 Jun 2014 19:35:24 -0400 From: Kevin Hilman To: Tomasz Figa Cc: Doug Anderson , Wolfram Sang , Kukjin Kim , Javier Martinez Canillas , naveen krishna , Jingoo Han , Jean Delvare , Simon Glass , Paul Gortmaker , Masanari Iida , Sachin Kamat , "linux-i2c\@vger.kernel.org" , "linux-arm-kernel\@lists.infradead.org" , linux-samsung-soc , "linux-kernel\@vger.kernel.org" Subject: Re: [PATCH] i2c: exynos5: Properly use the "noirq" variants of suspend/resume References: <1403155273-1057-1-git-send-email-dianders@chromium.org> <7h8uosyc3k.fsf@paris.lan> <7hwqcbs166.fsf@paris.lan> <7h7g4brx6w.fsf@paris.lan> <53A4CADA.4030002@gmail.com> <7ha993p8v4.fsf@paris.lan> <53A8AAC9.8030407@gmail.com> Date: Mon, 23 Jun 2014 16:35:21 -0700 In-Reply-To: <53A8AAC9.8030407@gmail.com> (Tomasz Figa's message of "Tue, 24 Jun 2014 00:31:37 +0200") Message-ID: <7hionrnqrq.fsf@paris.lan> User-Agent: Gnus/5.130008 (Ma Gnus v0.8) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Tomasz Figa writes: > On 24.06.2014 00:27, Doug Anderson wrote: >> Kevin, >> >> On Mon, Jun 23, 2014 at 3:19 PM, Kevin Hilman wrote: >>> Doug Anderson writes: >>> >>> [...] >>> >>>> On Fri, Jun 20, 2014 at 4:59 PM, Tomasz Figa wrote: >>>>> >>>>> I'm not sure noirq is going to work correctly, at least not with current >>>>> callbacks. I can see a call to clk_prepare_enable() there which needs to >>>>> acquire a mutex. >>>> >>>> Nice catch, thanks! :) >>>> >>>> OK, looking at that now. Interestingly this doesn't seem to cause us >>>> problems in our ChromeOS 3.8 tree. I just tried enabling: >>>> CONFIG_DEBUG_ATOMIC_SLEEP=y >>>> >>>> ...and confirmed that I got it on right: >>>> >>>> # zgrep -i atomic /proc/config.gz >>>> CONFIG_DEBUG_ATOMIC_SLEEP=y >>>> >>>> I can suspend/resume with no problems. My bet is that it works fine because: >>>> >>>> * resume_noirq is not considered "atomic" in the sense enforced by >>>> CONFIG_DEBUG_ATOMIC_SLEEP (at least not in 3.8--I haven't tried on >>>> ToT) >>> >>> The reason is because "noirq" in the suspend/resume path actually means >>> no *device* IRQs for that specific device. >>> >>> It's often assumed that the "noirq" callbacks are called with *all* >>> interrupts disabled, but that's not the case. Only the IRQs for that >>> specific device are disabled when its noirq callbacks run. >> >> Ah, so even with my fix of moving to noirq we could still be broken if >> the system decided to enable interrupts for the device before the i2c >> controller get resumed then we'd still be SOL. >> >> ...oh, but if it matches probe order then maybe we're guaranteed for >> that not to happen? We know that we will probe the i2c bus before the >> devices on it, right? > > If the mentioned device is a child of the I2C controller then the > parent-child relation determines the order. Otherwise (e.g. another, > non-I2C interrupt source that just triggers some operation on an I2C > device like voltage regulator) we're doomed. ;) Exactly. There are lots of dragons hiding here. Runtime PM is your friend. ;) Kevin