From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: "Li, Aubrey" <aubrey.li@linux.intel.com>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Linux PM list <linux-pm@vger.kernel.org>
Subject: Re: [PATCH] GPIO button wth wakeup attribute is supposed to wake the system up
Date: Wed, 09 Jul 2014 01:06:07 +0200
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On Tuesday, July 08, 2014 03:11:14 PM Dmitry Torokhov wrote:
> On Tue, Jul 08, 2014 at 11:47:01PM +0200, Rafael J. Wysocki wrote:
> > On Tuesday, July 08, 2014 02:12:59 PM Dmitry Torokhov wrote:
> > > On Tue, Jul 08, 2014 at 11:06:17PM +0200, Rafael J. Wysocki wrote:
> > > > On Tuesday, July 08, 2014 01:45:30 PM Dmitry Torokhov wrote:
> > > > > On Tue, Jul 08, 2014 at 10:52:52PM +0200, Rafael J. Wysocki wrote:
> > > > > > On Thursday, June 19, 2014 08:51:25 AM Li, Aubrey wrote:
> > > > > > > When the wakeup attribute is set, the GPIO button is capable of
> > > > > > > waking up the system from sleep states, including the "freeze"
> > > > > > > sleep state.  For that to work, its driver needs to pass the
> > > > > > > IRQF_NO_SUSPEND flag to devm_request_any_context_irq(), or the
> > > > > > > interrupt will be disabled by suspend_device_irqs() and the
> > > > > > > system won't be woken up by it from the "freeze" sleep state.
> > > > > > > 
> > > > > > > The suspend_device_irqs() routine is a workaround for drivers
> > > > > > > that mishandle interrupts triggered when the devices handled
> > > > > > > by them are suspended, so it is safe to use IRQF_NO_SUSPEND in
> > > > > > > all drivers that don't have that problem.
> > > > > > > 
> > > > > > > The affected/tested machines include Dell Venue 11 Pro and Asus T100TA.
> > > > > > > 
> > > > > > > Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com>
> > > > > > > Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > > > > 
> > > > > > OK
> > > > > > 
> > > > > > Due to the lack of response (ie. no objections) and because the issue
> > > > > > addressed by this patch is real, I'm queuing it up as a PM-related fix
> > > > > > for 3.17.
> > > > > 
> > > > > Please do not. The response is till the same: board code should make sure
> > > > > that enable_irq_wake() does the right thing and keeps interrupts enabled.
> > > > 
> > > > Which board code?  That's nothing like that for the platforms in question.
> > > 
> > > Then it needs to be written.
> > 
> > Well, excuse me, but I don't get it.  Why would I need to write any board code
> > for an ACPI-based system?
> 
> Why would not you? What is the difference between ACPI systems and all
> other systems? If ACPI-based systems need certain behavior they need to
> implement it, the same as DT-based systems or custom boards.

I'm not sure what you're talking about.

This isn't an ACPI-based system that needs certain behavior.  That's certain
behavior we want from GPIO buttons that can wake up *in* *general*.

Regardless of the platform, we want interrupts from those buttons to happen
after calling suspend_device_irqs().  Why?  Because we want them to be able
to happen while freeze_enter() is being executed and *that* is platform
independent.

> > > > > It is wrong to patch drivers for this.
> > > > 
> > > > Why is it?  Only drivers know if they can handle incoming interrupts after
> > > > having suspended their devices.
> > > 
> > > The driver correctly used enable_irq_wake() to indicate that interrupt should
> > > be a wakeup source, the now the core/board needs to make sure the interrupt
> > > gets delivered to the driver properly. We should not be patching every driver
> > > that uses enable_irq_wake() with IRQF_NO_SUSPEND.
> > 
> > Interrupts that can wake up from the "freeze" sleep state need not be set up
> > with enable_irq_wake() and the flag doesn't say "this is a wakeup interrupt".
> > It says "do not suspend this interrupt, I can handle it after the device has
> > been suspended" (as I said).
> 
> And the driver does not really care about this and whether the sleep
> state is suspend or freeze or something else, it is your platform that
> cares and has certain limitations that require interrupts to be not
> suspended in certain cases.

Not in "certain cases", but actually never and it is not about any platform
limitations.  I'm not sure what other words I need to use to make it more
clear.

> From the driver POV it says that the device can be a waekup source
> (again it does not care about details as to which sleep state we woudl
> be waking from) and it expects the PM core to handle the things
> properly. If certain sleep state requires interrupts to be kept on then
> PM core should make them as such, not driver.

That would be the case in an ideal world, but the real one is not ideal,
unfortunately.  The problem is that the PM core actually cannot decide
which interrupts to keep on, because it doesn't know which drivers can
cope with interrupts that happen after their devices have been suspended.
Using IRQF_NO_SUSPEND is the way to experess that by a driver.

And again, that has nothing to do with platform limitations or requirements.
All this is about is whether or not to allow interrupts to be *handled* by
drivers after certain point in the suspend sequence, which is
suspend_device_irqs().  By using IRQF_NO_SUSPEND drivers say, basically "it is
OK to leave this IRQ as is, I promise to take care of it going forward" and
that covers *all* suspend/hibernate transitions.

The reason why the "freeze" sleep state is somewhat special is that it doesn't
do any platform-specific magic and needs *normal* device interrupts to work
after suspend_device_irqs().  And I would *love* *to* drop suspend_device_irqs()
at this point, but I can't, because there still are drivers that would have
broken had I done that.

And I'm saying "somewhat" above, because that behavior is actually needed to
prevent wakeup events occuring *during* suspend transitions from being lost
for all kinds of those transitions (if someone actually cares).

> > 
> > And if it is OK for a driver to set IRQF_SHARED, it is equally OK for it to
> > set IRQF_NO_SUSPEND, because, in fact, those two flags are related.
> 
> Are you proposing for IRQ core to automatically set IRQF_NO_SUSPEND for
> IRQF_SHARED interrupts? That wold be fine with me.

No, I'm not.

The first choice basically is to go through all drivers that don't use IRQF_NO_SUSPEND
and which have _noirq suspend callbacks (that covers all PCI drivers and some
non-PCI ones too IIRC) and audit their interrupt handlers to check whether or not
they can cope with interrupts coming after their devices have been suspended.  Fix
the ones that can't and we can drop suspend_device_irqs().

But I guess I may be forgiven for regarding that as rather unattractive.  And we
actually could have done that to start with, guess why we didn't?

The second choice is to use IRQF_NO_SUSPEND in the drivers that are OK.  That
isn't too attractive either but has been practice for quite a while.

> > > If you look at the earlier patch discussion Tegra folks managed to implement
> > > this behavior just fine.
> > 
> > I'm not sure whose idea it was that IRQF_NO_SUSPEND was not to be set by drivers,
> > but it is not a correct one.  I know why suspend_device_irqs() was introduced
> > and I'm telling you this has nothing to do with setting up the IRQ chip to do
> > system wakeup.
> 
> I do not believe I asked why suspend_device_irqs() was introduced.

But you should, because suspend_device_irqs() is the very reason why
IRQF_NO_SUSPEND exists. :-)

> > 
> > And please grep for IRQF_NO_SUSPEND to see how drivers generally use it.
> 
> I see that just handful of them use IRQF_NO_SUSPEND (not sure how many
> are actully required), I see that a lot more drivers use
> enable_irq_wake() and do not bother setting IRQF_NO_SUSPEND.

And they will have problems with the "freeze" sleep state.

enable_irq_wake() is *not* a replacement for IRQF_NO_SUSPEND, nor the other
way around.  They are different things.

Rafael

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