Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751829AbaBWUCL (ORCPT ); Sun, 23 Feb 2014 15:02:11 -0500 Received: from mail-pb0-f53.google.com ([209.85.160.53]:60447 "EHLO mail-pb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751486AbaBWUCJ convert rfc822-to-8bit (ORCPT ); Sun, 23 Feb 2014 15:02:09 -0500 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT To: Lorenzo Pieralisi , "Russell King - ARM Linux" From: Sebastian Capella In-Reply-To: <20140222120910.GA9012@e102568-lin.cambridge.arm.com> Cc: "linux-kernel@vger.kernel.org" , "linux-pm@vger.kernel.org" , "linaro-kernel@lists.linaro.org" , "linux-arm-kernel@lists.infradead.org" , "Russ Dill" , "Rafael J. Wysocki" , "Len Brown" , "Pavel Machek" , "Nicolas Pitre" , "Santosh Shilimkar" , "Will Deacon" , "Cyril Chemparathy" , "Jonathan Austin" , "Catalin Marinas" , "Uwe Kleine-K?nig" , "Stephen Boyd" References: <1392774729-3235-1-git-send-email-sebastian.capella@linaro.org> <1392774729-3235-4-git-send-email-sebastian.capella@linaro.org> <20140219161254.GB19343@e102568-lin.cambridge.arm.com> <20140222103840.GH21483@n2100.arm.linux.org.uk> <20140222120910.GA9012@e102568-lin.cambridge.arm.com> Message-ID: <20140223200208.12998.47604@capellas-linux> User-Agent: alot/0.3.4 Subject: Re: [PATCH RFC v1 3/3] ARM hibernation / suspend-to-disk Date: Sun, 23 Feb 2014 12:02:08 -0800 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Lorenzo Pieralisi (2014-02-22 04:09:10) > On Sat, Feb 22, 2014 at 10:38:40AM +0000, Russell King - ARM Linux wrote: > > On Wed, Feb 19, 2014 at 04:12:54PM +0000, Lorenzo Pieralisi wrote: > > > On Wed, Feb 19, 2014 at 01:52:09AM +0000, Sebastian Capella wrote: > > > > +/* > > > > + * Snapshot kernel memory and reset the system. > > > > + * After resume, the hibernation snapshot is written out. > > > > + */ > > > > +static int notrace __swsusp_arch_save_image(unsigned long unused) > > > > +{ > > > > + int ret; > > > > + > > > > + ret = swsusp_save(); > > > > + if (ret == 0) > > > > + soft_restart(virt_to_phys(cpu_resume)); > > > > > > By the time the suspend finisher (ie this function) is run, the > > > processor state has been saved and I think that's all you have to do, > > > function can just return after calling swsusp_save(), unless I am missing > > > something. > > > > > > I do not understand why a soft_restart is required here. On a side note, > > > finisher is called with irqs disabled so, since you added a function for > > > soft restart noirq, it should be used, if needed, but I have to understand > > > why in the first place. > > > > It's required because you can't just return from the finisher. A normal > > return from the finisher will always be interpreted as an abort rather > > than success (because the state has to be unwound.) > > > > This is the only way to get a zero return from cpu_suspend(). > > Yes, that's the only reason why this code is jumping to cpu_resume, since > all it is needed is to snapshot the CPU context and by the time the > finisher is called that's done. Wanted to say that soft reboot is not > useful (cache flushing and resume with MMU off), but what you are saying > is correct. We might be saving swsusp_save return value in a global > variable and just return from the finisher, but that's horrible and > given the amount of time it takes to snapshot the image to disk the > cost of this soft reboot will be dwarfed by that. > > I wanted to ask and clarify why the code was written like this though, given > its complexity. We could also return a constant > 1. __cpu_suspend code will replace a 0 return with 1 for paths exiting suspend, but will not change return values != 0. cpu_suspend_abort: ldmia sp!, {r1 - r3} @ pop phys pgd, virt SP, phys resume fn teq r0, #0 moveq r0, #1 @ force non-zero value mov sp, r2 ldmfd sp!, {r4 - r11, pc} We could take advantage of that if we wanted, but Lorenzo pointed out also that the relative benefit is very low since the cost of resuming is >> soft_restart. I'll go with leaving the soft_restart as is unless someone feels strongly against. Thanks! Sebastian -- 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/