RE: [PATCH 1/3] ACPICA: Dispatch active GPEs at init time

[Zheng, Lv]

Hi,

> From: Rafael J. Wysocki [mailto:rjw@xxxxxxxxxxxxx]
> Subject: Re: [PATCH 1/3] ACPICA: Dispatch active GPEs at init time
> 
> On Friday, August 11, 2017 7:40:56 AM CEST Zheng, Lv wrote:
> > Hi, Rafael
> >
> > > From: Rafael J. Wysocki [mailto:rjw@xxxxxxxxxxxxx]
> > > Subject: Re: [PATCH 1/3] ACPICA: Dispatch active GPEs at init time
> > >
> > > On Thursday, August 10, 2017 3:48:58 AM CEST Zheng, Lv wrote:
> > > > Hi, Rafael
> > > >
> > > > > From: Rafael J. Wysocki [mailto:rjw@xxxxxxxxxxxxx]
> > > > > Subject: [PATCH 1/3] ACPICA: Dispatch active GPEs at init time
> > > > >
> > > > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > > >
> > > > > In some cases GPEs are already active when they are enabled by
> > > > > acpi_ev_initialize_gpe_block() and whatever happens next may depend
> > > > > on the result of handling the events signaled by them, so the
> > > > > events should not be discarded (which is what happens currently) and
> > > > > they should be handled as soon as reasonably possible.
> > > > >
> > > > > For this reason, modify acpi_ev_initialize_gpe_block() to
> > > > > dispatch GPEs with the status flag set in-band right after
> > > > > enabling them.
> > > >
> > > > In fact, what we need seems to be invoking acpi_ev_gpe_dispatch()
> > > > right after enabling an GPE. So there are 2 conditions related:
> > > > 1. GPE is enabled for the first time.
> > > > 2. GPE is initialized.
> > > >
> > > > And we need to make sure that before acpi_update_all_gpes() is invoked,
> > > > all GPE EN bits are actually disabled.
> > >
> > > But we don't do it today, do we?
> >
> > We don't do that.
> >
> > >
> > > And still calling _dispatch() should not be incorrect even if the GPE
> > > has been enabled already at this point.  Worst case it just will
> > > queue up the execution of _Lxx/_Exx which may or may not do anything
> > > useful.
> > >
> > > And BTW this is all done under acpi_gbl_gpe_lock so acpi_ev_gpe_detect()
> > > will block on it if run concurrently and we've checked the status, so
> > > we know that the GPE *should* be dispatched, so I sort of fail to see
> > > the problem.
> >
> > There is another problem related:
> > ACPICA clears GPEs before enabling it.
> > This is proven to be wrong, and we have to fix it:
> > https://bugzilla.kernel.org/show_bug.cgi?id=196249
> >
> > without fixing this issue, in this solution, we surely need to save the
> > GPE STS bit before incrementing GPE reference count, and poll it according
> > to the saved STS bit. Because if we poll it after enabling, STS bit will
> > be wrongly cleared.
> 
> I'm not sure if I understand you correctly, but why would we poll it?
> 
> In the $subject patch the status is checked and then
> acpi_ev_add_gpe_reference() is called to add a reference to the GPE.
> 
> If this is the first reference (which will be the case in the majority
> of cases), acpi_ev_enable_gpe() will be called and that will clear the
> status.
> 
> Then, acpi_ev_gpe_dispatch() is called if the status was set and that
> itself doesn't check the status.  It disables the GPE upfront (so the
> status doesn't matter from now on until the GPE is enabled again) and
> clears the status unconditionally if the GPE is edge-triggered.  This
> means that for edge-triggered GPEs the clearing of the status by
> acpi_ev_enable_gpe() doesn't matter here.

No problem, I understood.
And was thinking thought this patch [edge GPE dispatch fix] should be
correct and good for current Linux upstream.

What I meant is:
PATCH [edge GPE clear fix] https://patchwork.kernel.org/patch/9894983/
is a fix we need for upstream as it is the only possible fix for the
issue fixed by it.
On top of that, when acpi_ev_enable_gpe() is called, GPE won't be cleared.
and then things can be done in a simpler way:
PATCH [edge GPE enable fix] https://patchwork.kernel.org/patch/9894989/

As [edge GPE clear fix] is risky, I think [edge GPE dispatch fix] is OK
for Linux upstream.

So we can have 2 processes:
1. Merge [edge GPE dispatch fix] and let [edge GPE clear fix] and
   [edge GPE enable fix] released from ACPICA upstream so that:
   1. We can enhance them in ACPICA upstream.
   2. It will be regression safer for us to merge [edge GPE clear fix].
2. Merge [edge GPE clear fix] and [edge GPE enable fix] without
   merging [edge GPE dispatch fix].

What I meant is:
It's up to you to decide which process we should take. :)

> 
> For level-triggered GPEs the status is not cleared by acpi_ev_gpe_dispatch()
> itself, but _Lxx is executed (again, without checking the status) and
> finally the status is cleared by acpi_ev_finish_gpe() anyway, so we
> end up with cleared status no matter what (and that before re-enabling
> the GPE).  End even if _Lxx itself checked the status (but honestly why
> would it?), then this is a level-triggered GPE, so it will re-trigger
> anyway if not handled this time.

Let's skip level-triggered GPE case.

> 
> So it looks like the fact that acpi_ev_enable_gpe() clears the status before
> enabling the GPE doesn't matter for this patch, although it may matter in
> general, but that is a different (and somewhat related) issue.

I agreed.

Thanks and best regards
Lv