RE: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell systems

["Zheng, Lv" <lv.zheng@intel.com>]

Hi,

> From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net]
> Subject: Re: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell systems
> 
> On Thursday, May 04, 2017 04:23:30 PM Rafael J. Wysocki wrote:
> > On Thursday, May 04, 2017 07:58:53 AM Zheng, Lv wrote:
> > > Hi,
> > >
> > > > -----Original Message-----
> > > > From: linux-acpi-owner@vger.kernel.org [mailto:linux-acpi-owner@vger.kernel.org] On Behalf Of
> Rafael J.
> > > > Wysocki
> > > > Sent: Friday, April 28, 2017 6:26 AM
> > > > To: Mario.Limonciello@dell.com
> > > > Cc: linux-pm@vger.kernel.org; andriy.shevchenko@linux.intel.com; dvhart@infradead.org; linux-
> > > > kernel@vger.kernel.org; linux-acpi@vger.kernel.org; srinivas.pandruvada@linux.intel.com;
> > > > tglx@linutronix.de; mika.westerberg@linux.intel.com
> > > > Subject: Re: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell systems
> > > >
> > > > On Thursday, April 27, 2017 02:47:59 PM Mario.Limonciello@dell.com wrote:
> > > > > > -----Original Message-----
> > > > > > From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net]
> > > > > > Sent: Wednesday, April 26, 2017 4:24 PM
> > > > > > To: Linux PM <linux-pm@vger.kernel.org>
> > > > > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>; Darren Hart
> > > > > > <dvhart@infradead.org>; LKML <linux-kernel@vger.kernel.org>; Linux ACPI <linux-
> > > > > > acpi@vger.kernel.org>; Srinivas Pandruvada
> > > > > > <srinivas.pandruvada@linux.intel.com>; Thomas Gleixner <tglx@linutronix.de>;
> > > > > > Mika Westerberg <mika.westerberg@linux.intel.com>; Limonciello, Mario
> > > > > > <Mario_Limonciello@Dell.com>
> > > > > > Subject: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell
> > > > > > systems
> > > > > >
> > > > > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > > > >
> > > > > > Some recent Dell laptops, including the XPS13 model numbers 9360 and
> > > > > > 9365, cannot be woken up from suspend-to-idle by pressing the power
> > > > > > button which is unexpected and makes that feature hardly usable on
> > > > > > those systems.  However, on the 9365 ACPI S3 (suspend-to-RAM) is not
> > > > > > expected to be used at all (these systems ship with Windows 10 using
> > > > > > Modern Standby which never exercises the ACPI S3 path) and
> > > > > > suspend-to-idle is the only viable system suspend mechanism in there.
> > > > > >
> > > > > > The reason why the power button wakeup from suspend-to-idle doesn't
> > > > > > work on those systems is because their power button events are
> > > > > > signaled by the EC (Embedded Controller), whose GPE (General Purpose
> > > > > > Event) line is disabled during suspend-to-idle transitions in Linux.
> > > > > > That is done on purpose, because in general the EC tends to generate
> > > > > > tons of events for various reasons (battery and thermal updates and
> > > > > > similar, for example) and all of them would kick the CPUs out of deep
> > > > > > idle states while in suspend-to-idle, which would not be desirable.
> > > > > >
> > > > > > Of course, on the Dell systems in question the EC GPE must be enabled
> > > > > > during suspend-to-idle transitions for the button press events to
> > > > > > be signaled while suspended at all.  Fortunately, there is a way to
> > > > > > tell the EC to stop generating the non-wakeup events, which is by
> > > > > > using the _DSM object under the so called micro-PEP (uPEP) device
> > > > > > provided to support Modern Standby in Windows 10.
> > > > > >
> > > > > > The expected way to use it is to invoke function 0 from it on system
> > > > > > initialization, functions 3 and 5 during suspend transitions and
> > > > > > functions 4 and 6 during resume transitions (to reverse the actions
> > > > > > carried out by the former).  In particular, function 5 from the uPEP
> > > > > > device _DSM causes the EC to become less verbose (so to speak) on the
> > > > > > affected systems and then its GPE can be enabled as a wakeup source
> > > > > > (then, on resume, function 6 switches it back to the "working state"
> > > > > > mode).
> > > > > >
> > > > > > In support of the affected Dell systems, implement the uPEP device
> > > > > > handling as described and allow the EC to generate system wakeup
> > > > > > events if that device is present and behaves as expected.  Enable
> > > > > > that for Dell only, as there are other systems out there in which
> > > > > > the uPEP device is exposed in the ACPI tables and its _DSM appears
> > > > > > to be functional, but it actually isn't, whereas Dell is committed
> > > > > > to supporting it.
> > > > > >
> > > > >
> > > > > I am of course biased in that my priority is for this to work for Dell.
> > > > > Dell is definitely committed to supporting this on any system with
> > > > > the low power idle bit in the FADT set.
> > > > >
> > > > > So I'm fine with the current proposed solution, but have you
> > > > > dug into what actually breaks on this other system?  Does it actually
> > > > > work with Modern Standby + the uPEP device on Windows 10?
> > > > >
> > > > > To my understanding I would think any OEM that is enabling this
> > > > > uPEP device it should be getting called by the Windows kernel
> > > > > identically when entering resiliency phases.
> > > > >
> > > > > This makes me wonder if it should be inverted and a blacklist
> > > > > of platforms that the uPEP device doesn't work.
> > > >
> > > > For now I'd prefer to only do it on platforms where the benefit is clear.
> > > >
> > > > The next step may be to extend it to the other ones, but let's avoid making
> > > > what is problem mitigation really depend on things that may or may not
> > > > work elsewhere to start with.
> > >
> > > Then is it possible to invoke acpi_mark_gpe_for_wake() (and maybe also acpi_unmark_gpe_for_wake())
> right after invoking uPEP functions?
> > > So that such platform specific stuffs won't go into ec.c.
> >
> > I'm not sure ATM, but it should be doable in theory.
> 
> So the problem with that is that the EC GPE number is not known to the sleep.c
> code, so it would need to be exported by the EC driver somehow or similar,
> which would be uglier than the current patch IMO.

Ah, I see.
Anyway, this is not urgent.
We can just focus on user issue now.

Thanks and best regards
Lv