[systemd-devel] [WIP PATCH 0/4] Rework the unreliable LID switch exported by ACPI

[Zheng, Lv]

Hi, Peter

> From: Peter Hutterer [mailto:peter.hutterer at who-t.net]
> Subject: Re: [systemd-devel] [WIP PATCH 0/4] Rework the unreliable LID switch exported by ACPI
> 
> On Thu, Jun 15, 2017 at 02:52:57AM +0000, Zheng, Lv wrote:
> > Hi, Benjamin
> >
> > > From: Benjamin Tissoires [mailto:benjamin.tissoires at redhat.com]
> > > Subject: Re: [systemd-devel] [WIP PATCH 0/4] Rework the unreliable LID switch exported by ACPI
> > >
> > > Hi,
> > >
> > > [Sorry for the delay, I have been sidetracked from this]
> > >
> > > On Jun 07 2017 or thereabouts, Lennart Poettering wrote:
> > > > On Thu, 01.06.17 20:46, Benjamin Tissoires (benjamin.tissoires at redhat.com) wrote:
> > > >
> > > > > Hi,
> > > > >
> > > > > Sending this as a WIP as it still need a few changes, but it mostly works as
> > > > > expected (still not fully compliant yet).
> > > > >
> > > > > So this is based on Lennart's comment in [1]: if the LID state is not reliable,
> > > > > the kernel should not export the LID switch device as long as we are not sure
> > > > > about its state.
> > > >
> > > > Ah nice! I (obviously) like this approach.
> > >
> > > Heh. Now I just need to convince Lv that it's the right approach.
> >
> > I feel we don't have big conflicts.
> > And I already took part of your idea into this patchset:
> > https://patchwork.kernel.org/patch/9771121/
> > https://patchwork.kernel.org/patch/9771119/
> > I tested my surface pros with Ubuntu, they are working as expected.
> >
> > > > > Note that systemd currently doesn't sync the state when the input node just
> > > > > appears. This is a systemd bug, and it should not be handled by the kernel
> > > > > community.
> > > >
> > > > Uh if this is borked, we should indeed fix this in systemd. Is there
> > > > already a systemd github bug about this? If not, please create one,
> > > > and we'll look into it!
> > >
> > > I don't think there is. I haven't raised it yet because I am not so sure
> > > this will not break again those worthless unreliable LID, and if we play
> > > whack a mole between the kernel and user space, things are going to be
> > > nasty. So I'd rather have this fixed in systemd along with the
> > > unreliable LID switch knowledge, so we are sure that the kernel behaves
> > > the way we expect it to be.
> >
> > This is my feeling:
> > We needn't go that far.
> > We can interpret "input node appears" into "default input node state".
> 
> Sorry, can you clarify this bit please? I'm not sure what you mean here.
> Note that there's an unknown amount of time between "device node appearing
> in the system" and when a userspace process actually opens it and looks at
> its state. By then, the node may have changed state again.

We can see:
"logind" has already implemented a timeout, and will not respond lid state
unless it can be stable within this timeout period.
I'm not an expert of logind, maybe this is because of "HoldOffTimeoutSec"?

I feel "removing the input node for a period where its state is not trustful"
is technically identical to this mechanism.

Cheers,
Lv

> 
> Cheers,
>    Peter
> 
> > That's what you want for acpi button driver - we now defaults to "method" mode.
> >
> > What's your opinion?
> >
> > Thanks
> > Lv
> >