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

Zheng, Lv
2017-06-16T08:53:36Z

Hi,

> From: Benjamin Tissoires [mailto:benjamin.tissoires@redhat.com]
> Subject: Re: [systemd-devel] [WIP PATCH 0/4] Rework the unreliable LID switch exported by ACPI
>
> On Jun 16 2017 or thereabouts, Zheng, Lv wrote:
> > Hi, Benjamin
> >
> > Let me just say something one more time.
> >
> > > From: Benjamin Tissoires [mailto:benjamin.tissoires@redhat.com]
>
> [snip]
> > > > > >
> > > > > > 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.
> > > >
> > > > Do you see practical issues?
> > >
> > > Yes, libinput can't rely on the LID switch information to disable
> > > touchpads/touchscreens that are potentially sending false positive.
> >
> > "potential" doesn't mean "practical", right?
>
> I was using potential to say that some actual devices are sending
> rightful states, while others are not (we already named them a lot in
> those countless threads). So potential here is from a user space
> perspective where you are not sure if the state is reliable or not
> (given we currently don't have this information about reliability).
>
> > After applying my last version.
> > There are no false-positives IMO.
> > There are only delays for the reliable key events.
> > ^^^^^^
> > While the "delay" is very common in computing world.
>
> No, if there is a delay, there is a false positive, because the initial
> state is wrong with respect to the device physical state.
>
> >
> > > > After resume, SW_LID state could remain unreliable "close" for a while.
> > >
> > > This is not an option. It is not part of the protocol, having an
> > > unreliable state.
> > >
> > > > But that's just a kind of delay happens in all computing programs.
> > > > I suppose all power managing programs have already handled that.
> > > > I confirmed no breakage for systemd 233.
> > > > For systemd 229, it cannot handle it well due to bugs.
> > > > But my latest patch series has worked the bug around.
> > > > So I don't see any breakage related to post-resume incorrect state period.
> > > > Do you see problems that my tests haven't covered?
> > >
> > > The problems are that you are not following the protocol. And if systemd
> > > 233 works around it, that's good, but systemd is not the only listener
> > > of the LID switch input node, and you are still breaking those by
> > > refusing to follow the specification of the evdev protocol.
> >
> > As you are talking about protocol, let me just ask once.
> >
> > In computing world,
> > 1. delay is very common
> > There are bus turnaround, network turnaround, ...
> > Even measurement itself has delay described by Shannon sampling.
> > Should the delay be a part of the protocol?
>
> Please, you are either trolling or just kidding. If there are delays in
> the "computing world", these has to be handled by the kernel, and not
> exported to the user space if the kernel protocol says that the state is
> reliable.
>
> > 2. programs are acting according to rules (we call state machines)
> > States are only determined after measurement (like "quantum states")
> > I have Schroedinger's cat in my mind.
> > Events are determined as they always occur after measurement to trigger "quantum jumps".
> > So for EV_SW protocol,
> > Should programs rely on the reliable "quantum jumps",
> > Or should programs rely on the unreliable "quantum states"?
>
> No comments, this won't get us anywhere.
>
> >
> > I think most UI programs care no about state stored in the input node,
> > they only receive events raised from the input node.
>
> Bullshit. When you launch such a program, you need to query the state
> because you won't receive the event that happened way before the launch.
>
> > Why should the kernel export a fade-in/fade-out input node to the UI programs and ask them to change?
> >
> > The only program that cares about the state stored in the input node is libinput.
> > So why should every user program be changed to make libinput easier?
>
> No, all program that listen to LID switches input nodes care about the
> state. We already told you that, you just don't listen:
>
> - systemd cares about the state as it does polling on the input node in
> case it misses an event
> - libinput cares about the state as previously mentioned
> - gnome-setting-daemons cares about the state given it decides whether
> or not lighting up the monitors depending on the state. And if you
> relaunch the daemon, it'll query the state to decide what is the best
> arrangement for the screens

Let's consider this case with delay:
After resume, gnome-setting-daemon queries SW_LID and got "close".
Then it lights up the wrong monitors.
Then I believe "open" will be delivered to it several seconds later.
Should gnome-setting-daemon light-up correct monitors this time?
So it just looks like user programs behave with a delay accordingly because of the "platform turnaround" delay.

> - KDE should do the same (as it is not a daemon that can catch any
> events)

Cheers,
Lv