From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752449AbbBKOcn (ORCPT ); Wed, 11 Feb 2015 09:32:43 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:56707 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751829AbbBKOcm (ORCPT ); Wed, 11 Feb 2015 09:32:42 -0500 From: "Rafael J. Wysocki" To: Boris Brezillon Cc: Mark Rutland , Thomas Gleixner , Jason Cooper , Nicolas Ferre , Jean-Christophe Plagniol-Villard , Alexandre Belloni , Rob Herring , Pawel Moll , Ian Campbell , Kumar Gala , "devicetree@vger.kernel.org" , "Rafael J. Wysocki" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Alexandre Belloni Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip Date: Wed, 11 Feb 2015 15:55:47 +0100 Message-ID: <2982569.CIWvqghzfx@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20150211132437.0753a7da@bbrezillon> References: <1422527620-8308-1-git-send-email-boris.brezillon@free-electrons.com> <20150211111106.GA9154@leverpostej> <20150211132437.0753a7da@bbrezillon> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday, February 11, 2015 01:24:37 PM Boris Brezillon wrote: > Hi Mark, > > On Wed, 11 Feb 2015 11:11:06 +0000 > Mark Rutland wrote: > > > On Wed, Feb 11, 2015 at 08:53:39AM +0000, Boris Brezillon wrote: > > > Hi Mark, > > > > > > On Tue, 10 Feb 2015 20:48:36 +0000 > > > Mark Rutland wrote: > > > > > > > On Tue, Feb 10, 2015 at 03:52:01PM +0000, Boris Brezillon wrote: > > > > > Hi Mark, > > > > > > > > > > On Tue, 10 Feb 2015 15:36:28 +0000 > > > > > Mark Rutland wrote: > > > > > > > > > > > Hi Boris, > > > > > > > > > > > > On Thu, Jan 29, 2015 at 10:33:38AM +0000, Boris Brezillon wrote: > > > > > > > Add documentation for the virtual irq demuxer. > > > > > > > > > > > > > > Signed-off-by: Boris Brezillon > > > > > > > Acked-by: Nicolas Ferre > > > > > > > --- > > > > > > > .../bindings/interrupt-controller/dumb-demux.txt | 41 ++++++++++++++++++++++ > > > > > > > 1 file changed, 41 insertions(+) > > > > > > > create mode 100644 Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt > > > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt b/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt > > > > > > > new file mode 100644 > > > > > > > index 0000000..b9a7830 > > > > > > > --- /dev/null > > > > > > > +++ b/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt > > > > > > > @@ -0,0 +1,41 @@ > > > > > > > +* Virtual Interrupt Demultiplexer > > > > > > > + > > > > > > > +This virtual demultiplexer simply forward all incoming interrupts to its > > > > > > > +enabled/unmasked children. > > > > > > > +It is only intended to be used by hardware that do not provide a proper way > > > > > > > +to demultiplex a source interrupt, and thus have to wake all their children > > > > > > > +up so that they can possibly handle the interrupt (if needed). > > > > > > > +This can be seen as an alternative to shared interrupts when at least one > > > > > > > +of the interrupt children is a timer (and require the irq to stay enabled > > > > > > > +on suspend) while others are not. This will prevent calling irq handlers of > > > > > > > +non timer devices while they are suspended. > > > > > > > > > > > > This sounds like a DT-workaround for a Linux implementation problem, and > > > > > > I don't think this the right way to solve your problem. > > > > > > > > > > I understand your concern, but why are you answering while I asked for > > > > > DT maintainers reviews for several days (if not several weeks). > > > > > > > > > > > > > > > > > Why does this have to be in DT at all? Why can we not fix the core to > > > > > > handle these details? > > > > > > > > > > We already discussed that with Rob and Thomas, and hiding such a > > > > > demuxer chip is not an easy task. > > > > > I'm open to any suggestion to do that, though I'd like you (I mean DT > > > > > guys) to provide a working implementation (or at least a viable concept) > > > > > that would silently demultiplex an irq. > > > > > > > > > > > > > > > > > I am very much not keen on this binding. > > > > > > > > > > Yes, but do you have anything else to propose. > > > > > We're experiencing this warning for 2 releases now, and this is time to > > > > > find a solution (even if it's not a perfect one). > > > > > > > > Thoughts on the patch below? > > > > > > That's pretty much what I proposed in my first attempt to solve this > > > problem [1] (except for a few things commented below). > > > Anyway, Thomas suggested to go for the "dumb/virt irq demultiplexer" > > > approach instead. > > > > There is one fundamental difference in that this patch does not require > > drivers to be updated (the new flag is only used internally). Which > > avoids having to patch every single driver that could possibly be used > > in combination with one wanting interrupts during suspend. > > Actually, that was one of the requirements expressed by Thomas (Thomas, > correct me if I'm wrong). > The point was to force shared irq users to explicitly specify that they > are mixing !IRQF_NO_SUSPEND and IRQF_NO_SUSPEND because they have no > other choice. > > With your patch, there's no way to inform users that they are > erroneously setting the IRQF_NO_SUSPEND flag on one of their shared > interrupt. > > > > > Any used which did not explicitly request with IRQF_NO_SUSPEND will not > > receive interrupts during suspend. > > > > [...] > > > > > > +static irqreturn_t __handle_irq_event_percpu(unsigned int irq, struct irqaction *action) > > > > +{ > > > > + /* > > > > + * During suspend we must not call potentially unsafe irq handlers. > > > > + * See suspend_suspendable_actions. > > > > + */ > > > > + if (unlikely(action->flags & IRQF_NO_ACTION)) > > > > + return IRQ_NONE; > > > > > > Thomas was trying to avoid any new conditional code in the interrupt > > > handling path, that's why I added a suspended_action list in my > > > proposal. > > > Even if your 'unlikely' statement make things better I'm pretty sure it > > > adds some latency. > > > > I can see that we don't want to add more code here to keep things > > clean/pure, but I find it hard to believe that a single bit test and > > branch (for data that should be hot in the cache) are going to add > > measurable latency to a path that does pointer chasing to get to the > > irqaction in the first place. I could be wrong though, and I'm happy to > > benchmark. > > Again, I don't have enough experience to say this is (or isn't) > impacting irq handling latency, I'm just reporting what Thomas told me. > > > > > It would be possible to go for your list shuffling approach here while > > still keeping the flag internal and all the logic hidden away in > > kernel/irq/pm.c. I wasn't sure how actions could be manipulated during > > suspend, which made me wary of moving them to a separate list. > > Moving them to a temporary list on suspend and restoring them on > resume should not be a problem. > The only drawback I see is that actions might be reordered after the > first resume (anyway, relying on shared irq action order is dangerous > IMHO). We considered doing that too and saw some drawbacks (in addition to the reordering of actions you've mentioned). It added just too much complexity to the IRQ suspend-resume code. I, personally, would be fine with adding an IRQ flag to silence the warning mentioned by Alexandre. Something like IRQD_TIMER_SHARED that would be set automatically if someone requested IRQF_TIMER | IRQF_SHARED. Thoughts? Rafael