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From: Boris Brezillon <boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
To: "Rafael J. Wysocki" <rjw-LthD3rsA81gm4RdzfppkhA@public.gmane.org>
Cc: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Jason Cooper <jason-NLaQJdtUoK4Be96aLqz0jA@public.gmane.org>,
	Nicolas Ferre
	<nicolas.ferre-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org>,
	Jean-Christophe Plagniol-Villard
	<plagnioj-sclMFOaUSTBWk0Htik3J/w@public.gmane.org>,
	Alexandre Belloni
	<alexandre.belloni-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>,
	Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Pawel Moll <Pawel.Moll-5wv7dgnIgG8@public.gmane.org>,
	Ian Campbell
	<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
	Kumar Gala <galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
	"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"Rafael J. Wysocki"
	<rafael.j.wysocki-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
	<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
	"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip
Date: Wed, 11 Feb 2015 15:45:30 +0100	[thread overview]
Message-ID: <20150211154530.24abb00e@bbrezillon> (raw)
In-Reply-To: <2982569.CIWvqghzfx-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>

On Wed, 11 Feb 2015 15:55:47 +0100
"Rafael J. Wysocki" <rjw-LthD3rsA81gm4RdzfppkhA@public.gmane.org> wrote:

> 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 <mark.rutland-5wv7dgnIgG8@public.gmane.org> 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 <mark.rutland-5wv7dgnIgG8@public.gmane.org> 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 <mark.rutland-5wv7dgnIgG8@public.gmane.org> 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 <boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> > > > > > > > Acked-by: Nicolas Ferre <nicolas.ferre-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org>
> > > > > > > > ---
> > > > > > > >  .../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.

Yep, but that won't prevent irq handler from being called (even when
they are suspended), and IIRC, that was one of Thomas' concerns.
This shouldn't be a problem for the at91 platform though (actually, this
is the current behavior).


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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  parent reply	other threads:[~2015-02-11 14:45 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-29 10:33 [PATCH v4 0/5] ARM: at91: fix irq_pm_install_action WARNING Boris Brezillon
     [not found] ` <1422527620-8308-1-git-send-email-boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
2015-01-29 10:33   ` [PATCH v4 1/5] genirq: Authorize chained handlers to remain disabled when initialized Boris Brezillon
2015-01-29 10:33 ` [PATCH v4 2/5] irqchip: add virtual demultiplexer implementation Boris Brezillon
2015-02-10 15:00   ` Peter Zijlstra
2015-02-10 15:20     ` Boris Brezillon
2015-02-10 15:43     ` [PATCH] genirq: fix virtual irq demuxer related comments Boris Brezillon
     [not found]       ` <1423582992-8154-1-git-send-email-boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
2015-02-10 16:14         ` Peter Zijlstra
2015-02-20 16:12           ` Mark Rutland
2015-02-20 16:17             ` Peter Zijlstra
     [not found]   ` <1422527620-8308-3-git-send-email-boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
2015-02-10 15:48     ` [PATCH v4 2/5] irqchip: add virtual demultiplexer implementation Mark Rutland
2015-01-29 10:33 ` [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip Boris Brezillon
2015-02-10 15:36   ` Mark Rutland
2015-02-10 15:52     ` Boris Brezillon
2015-02-10 16:06       ` Boris Brezillon
2015-02-10 16:16       ` Mark Rutland
2015-02-10 16:20         ` Boris Brezillon
2015-02-10 20:48       ` Mark Rutland
2015-02-11  8:53         ` Boris Brezillon
2015-02-11 11:11           ` Mark Rutland
2015-02-11 12:24             ` Boris Brezillon
2015-02-11 12:36               ` Mark Rutland
2015-02-11 13:38                 ` Alexandre Belloni
     [not found]                   ` <20150211133859.GC3971-m++hUPXGwpdeoWH0uzbU5w@public.gmane.org>
2015-02-11 13:48                     ` Mark Rutland
2015-02-11 14:55               ` Rafael J. Wysocki
2015-02-11 14:43                 ` Mark Rutland
2015-02-11 15:17                   ` Rafael J. Wysocki
     [not found]                     ` <2437801.56xPyk3atd-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>
2015-02-11 15:03                       ` Boris Brezillon
2015-02-11 15:39                         ` Rafael J. Wysocki
2015-02-11 15:23                           ` Mark Rutland
2015-02-11 15:12                     ` Mark Rutland
2015-02-11 15:51                       ` Rafael J. Wysocki
2015-02-11 15:57                         ` Mark Rutland
2015-02-11 16:15                           ` Boris Brezillon
2015-02-11 16:32                             ` Mark Rutland
2015-02-11 16:38                               ` Boris Brezillon
2015-02-11 17:17                                 ` Mark Rutland
2015-02-20 14:22                                 ` Mark Rutland
2015-02-20 14:53                                   ` Boris Brezillon
2015-02-20 15:16                                     ` Mark Rutland
2015-02-23 17:00                                       ` Boris Brezillon
2015-02-23 18:14                                         ` Mark Rutland
2015-02-23 20:16                                           ` Boris Brezillon
2015-02-11 16:42                             ` Rafael J. Wysocki
2015-02-11 16:28                               ` Boris Brezillon
     [not found]                               ` <2067295.NbJCftPPli-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>
2015-02-11 17:13                                 ` Mark Rutland
2015-02-11 17:29                                   ` Boris Brezillon
2015-02-12 10:52                                     ` Mark Rutland
2015-02-12 11:09                                       ` Boris Brezillon
2015-02-12 11:23                                         ` Mark Rutland
2015-02-16  9:49                                   ` Peter Zijlstra
2015-02-16  9:28                         ` Peter Zijlstra
     [not found]                           ` <20150216092814.GF7119-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2015-02-16 12:23                             ` Mark Rutland
2015-02-19  1:16                               ` Rafael J. Wysocki
     [not found]                                 ` <2502710.nOuZfdq5QP-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>
2015-02-19 11:23                                   ` Mark Rutland
2015-02-19 22:35                                     ` Rafael J. Wysocki
2015-02-20 10:31                                       ` Mark Rutland
2015-02-24  1:02                                         ` Rafael J. Wysocki
2015-02-24  8:42                                           ` Boris Brezillon
     [not found]                 ` <2982569.CIWvqghzfx-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>
2015-02-11 14:45                   ` Boris Brezillon [this message]
2015-02-11 14:39             ` Rafael J. Wysocki
2015-02-11  9:11         ` Peter Zijlstra
2015-02-11 11:15           ` Mark Rutland
2015-02-11 14:31             ` Rafael J. Wysocki
     [not found]               ` <32372622.IiYZ15O7e1-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>
2015-02-11 14:14                 ` Mark Rutland
2015-02-11 15:07                   ` Rafael J. Wysocki
     [not found]                     ` <1448858.4nScWhYZcX-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org>
2015-02-11 15:03                       ` Mark Rutland
2015-02-11 14:34         ` Rafael J. Wysocki
2015-01-29 10:33 ` [PATCH v4 4/5] ARM: at91/dt: select VIRT_IRQ_DEMUX for all at91 SoCs Boris Brezillon
2015-01-29 10:33 ` [PATCH v4 5/5] ARM: at91/dt: define a virtual irq demultiplexer chip connected on irq1 Boris Brezillon
2015-02-09 15:47 ` [PATCH v4 0/5] ARM: at91: fix irq_pm_install_action WARNING Boris Brezillon

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