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

[Peter Hutterer <peter.hutterer@who-t.net>]

On Thu, Jun 15, 2017 at 07:33:58AM +0000, Zheng, Lv wrote:
> Hi, Peter
> 
> > From: Peter Hutterer [mailto:peter.hutterer@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@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@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.

but you'd be making kernel policy based on one userspace implementation.
e.g. libinput doesn't have a timeout period, it assumes the state is
correct when an input node is present. 

Cheers,
   Peter