linux-kernel - Re: [PATCH 4.19 085/271] ACPICA: Clear status of GPEs on first direct enable

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Date:   Sat, 27 Jul 2019 12:51:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@....cz>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Furquan Shaikh <furquan@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 085/271] ACPICA: Clear status of GPEs on first
 direct enable

On Fri, Jul 26, 2019 at 07:57:06PM +0200, Pavel Machek wrote:
> On Wed 2019-07-24 21:19:14, Greg Kroah-Hartman wrote:
> > [ Upstream commit 44758bafa53602f2581a6857bb20b55d4d8ad5b2 ]
> > 
> > ACPI GPEs (other than the EC one) can be enabled in two situations.
> > First, the GPEs with existing _Lxx and _Exx methods are enabled
> > implicitly by ACPICA during system initialization.  Second, the
> > GPEs without these methods (like GPEs listed by _PRW objects for
> > wakeup devices) need to be enabled directly by the code that is
> > going to use them (e.g. ACPI power management or device drivers).
> > 
> > In the former case, if the status of a given GPE is set to start
> > with, its handler method (either _Lxx or _Exx) needs to be invoked
> > to take care of the events (possibly) signaled before the GPE was
> > enabled.  In the latter case, however, the first caller of
> > acpi_enable_gpe() for a given GPE should not be expected to care
> > about any events that might be signaled through it earlier.  In
> > that case, it is better to clear the status of the GPE before
> > enabling it, to prevent stale events from triggering unwanted
> > actions (like spurious system resume, for example).
> 
> Given the complexity of ACPI and number of implementations, I don't
> think this is safe for stable.

So it's better to have a regression later rather than sooner?

> Notebooks are not part of automated test farms, so it did not get
> nearly enough testing...

But by finding problems with a patch when it is closer to having been
created is always better than waiting 6+ months to find the issue then.

And if this patch does cause problems, we can easily revert it.

thanks,

greg k-h