From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 196E0C5CFFE for ; Tue, 11 Dec 2018 14:16:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE46120849 for ; Tue, 11 Dec 2018 14:16:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DE46120849 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726833AbeLKOQg (ORCPT ); Tue, 11 Dec 2018 09:16:36 -0500 Received: from foss.arm.com ([217.140.101.70]:48198 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726448AbeLKOQg (ORCPT ); Tue, 11 Dec 2018 09:16:36 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 426F61596; Tue, 11 Dec 2018 06:16:35 -0800 (PST) Received: from e107981-ln.cambridge.arm.com (e107981-ln.cambridge.arm.com [10.1.197.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2B0FF3F59C; Tue, 11 Dec 2018 06:16:32 -0800 (PST) Date: Tue, 11 Dec 2018 14:16:27 +0000 From: Lorenzo Pieralisi To: "Rafael J. Wysocki" , sboyd@kernel.org Cc: Miquel Raynal , sudeep.holla@arm.com, Gregory Clement , Jason Cooper , Andrew Lunn , Sebastian Hesselbarth , Thomas Petazzoni , Bjorn Helgaas , devicetree@vger.kernel.org, Rob Herring , Mark Rutland , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Antoine Tenart , Maxime Chevallier , Nadav Haklai Subject: Re: [PATCH 05/12] PCI: aardvark: add suspend to RAM support Message-ID: <20181211141627.GA526@e107981-ln.cambridge.arm.com> References: <20181123141831.8214-1-miquel.raynal@bootlin.com> <1999610.6DN9RK2Tt3@aspire.rjw.lan> <20181204094558.GA24588@e107981-ln.cambridge.arm.com> <1966692.fVZYlVgWHv@aspire.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1966692.fVZYlVgWHv@aspire.rjw.lan> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 04, 2018 at 10:42:19PM +0100, Rafael J. Wysocki wrote: > On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote: > > On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote: > > > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote: > > > > Hi Lorenzo, > > > > > > > > Lorenzo Pieralisi wrote on Mon, 3 Dec 2018 > > > > 10:27:08 +0000: > > > > > > > > > [+Rafael, Sudeep] > > > > > > > > > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote: > > > > > > Add suspend and resume callbacks. The priority of these are > > > > > > "_noirq()", to workaround early access to the registers done by the > > > > > > PCI core through the ->read()/->write() callbacks at resume time. > > > > > > > > > > > > Signed-off-by: Miquel Raynal > > > > > > --- > > > > > > drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++ > > > > > > 1 file changed, 52 insertions(+) > > > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > > > index 108b3f15c410..7ecf1ac4036b 100644 > > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pci > > > > > > return ret; > > > > > > } > > > > > > > > > > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev) > > > > > > +{ > > > > > > + struct advk_pcie *pcie = dev_get_drvdata(dev); > > > > > > + > > > > > > + advk_pcie_disable_phy(pcie); > > > > > > + > > > > > > + clk_disable_unprepare(pcie->clk); > > > > > > > > > > I have noticed it is common practice, still, I would like to check whether > > > > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume > > > > > callback ? > > > > > > > > You are right this is weird. I double checked and for instance, > > > > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are > > > > probably other cases where drivers call functions that may sleep from a NOIRQ > > > > context. I am interested to know if this is valid and if not, what is the > > > > alternative? > > > > > > > > > > Yes, it is valid. _noirq means that the high-level action handlers > > > will not be invoked for interrupts occurring during that period, but > > > that doesn't apply to timer interrupts. > > > > > > IOW, don't expect *your* IRQ handler to be invoked then (if this is > > > not a timer IRQ), but you can sleep. > > > > Hi Rafael, all, > > > > I did not ask my question (that may be silly) properly apologies. I know > > that the S2R context allows sleeping the question is, in case > > clk_disable_unprepare() (and resume counterparts) sleeps, > > If it just sleeps, then this is not a problem, but if it actually *waits* > for something meaningful to happen (which I guess is what you really mean), > then things may go awry. > > > what is going to wake it up, given that we are in the S2R NOIRQ phase and as > > you said the action handlers (that are possibly required to wake up the eg > > clk_disable_unprepare() caller) are disabled (unless, AFAIK, > > IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver). > > So if it waits for an action handler to do something and wake it up, it may > very well deadlock. I have no idea if that really happens, though. > > > The clk API implementations back-ends are beyond my depth, I just wanted > > to make sure I understand how the S2R flow is expected to work in this > > specific case. > > Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND > (well, there are a few more complications I don't recall exactly, but > that's the basic rule). If anything depends on them to run, it will block. Stephen, any comments on this ? I would like to understand if it is safe to call a clk_*unprepare/prepare_* function (that may have a blocking back-end waiting on a wake-up event triggered by an IRQ action) in the suspend/resume NOIRQ phase. It is not clear how the unprepare/prepare() callers can possibly know whether it is safe to block at that stage given that IRQ actions are suspended and the wake-up may never trigger. Thanks, Lorenzo