linux-kernel - Re: [WIP PATCH 2/4] ACPI: button: remove the LID input node when the state is unknown

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Date:   Wed, 7 Jun 2017 11:27:50 +1000
From:   Peter Hutterer <peter.hutterer@...-t.net>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     "Zheng, Lv" <lv.zheng@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "systemd-devel@...ts.freedesktop.org" 
        <systemd-devel@...ts.freedesktop.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>
Subject: Re: [WIP PATCH 2/4] ACPI: button: remove the LID input node when the
 state is unknown

On Tue, Jun 06, 2017 at 12:22:09PM +0200, Benjamin Tissoires wrote:
[...]
> > This is because the aml table puts many Notify(LID, 0x80) in various control methods.
> > And not one of them but multiple of them will be invoked by various OS drivers during suspend/resume period.
> > I think this is not an isolated platform that will invoke multiple redundant "Notify(lid)".
> > 
> > Fortunately, the lid state for the multiple notify(lid) should be same as the first "Notify(lid)".
> > I suppose this is why SW_LID is invented, as it can really filter such redundant events.
> > And user space finally can only see 1 "close" event.
> > 
> > But unconditionally prepending "open" before all "close" events surely can break the logic by
> > delivering multiple "close" events to the user space.
> 
> That doesn't matter. What matters is the state of the switch, not the
> event. So if user space receives (in case we marked the switch as not
> reliable) several close events, all user space will do is realize that
> the state is still closed and will act accordingly.

[...]

> Again, we don't care if the "event" comes from ACPI, the driver itself or
> user space (libinput). All that matters is the current state of the
> input node switch, that needs to match the physical world at any time.

as extra comment on those two: you cannot guarantee when e.g. libinput
checks the state. it may start up after the kernel has updated the EV_SW
state, it may close and re-open a device without notice (disabling a
device in X has that effect for example). So the EV_SW/SW_LID events are
nice to have, but we really rely on the *state* of the switch more than the
events.

Cheers,
   Peter