Date:   Wed, 10 Jun 2020 15:52:15 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
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        patches@...nsource.cirrus.com,
        ibm-acpi-devel@...ts.sourceforge.net,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
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Subject: Re: [PATCH v4 0/7] Support inhibiting input devices

Hi,

On 6/10/20 12:38 PM, Rafael J. Wysocki wrote:
> On Wed, Jun 10, 2020 at 11:50 AM Hans de Goede <hdegoede@...hat.com> wrote:

<snip>

>> A different, but related issue is how to make devices actually use the
>> new inhibit support on the builtin keyboard + touchpad when say the lid
>> is closed.   Arguably this is an userspace problem, but it is a tricky
>> one. Currently on most modern Linux distributions suspend-on-lid-close
>> is handled by systemd-logind and most modern desktop-environments are
>> happy to have logind handle this for them.
>>
>> But most knowledge about input devices and e.g. heurisitics to decide
>> if a touchpad is internal or external are part of libinput. Now we could
>> have libinput use the new inhibit support (1), but then when the lid
>> closes we get race between whatever process is using libinput trying
>> to inhibit the touchpad (which must be done before to suspend to disable
>> it as wakeup source) and logind trying to suspend the system.
>>
>> One solution here would be to move the setting of the inhibit sysfs
>> attr into logind, but that requires adding a whole bunch of extra
>> knowledge to logind which does not really belong there IMHO.
>>
>> I've been thinking a bit about this and to me it seems that the kernel
>> is in the ideal position to automatically inhibit some devices when
>> some EV_SW transitions from 0->1 (and uninhibit again on 1->0). The
>> issue here is to chose on which devices to enable this. I believe
>> that the auto inhibit on some switches mechanism is best done inside
>> the kernel (disabled by default) and then we can have a sysfs
>> attr called auto_inhibit_ev_sw_mask which can be set to e.g.
>> (1 << SW_LID) to make the kernel auto-inhibit the input-device whenever
>> the lid is closed, or to ((1 << SW_LID) | (1 << SW_TABLET_MODE)) to
>> inhibit both when the lid is closed or when switched to tablet mode.
> 
> I agree that the kernel is the right place to handle this, but it
> requires some extra knowledge about dependencies between devices.
>
> It'd be kind of like power resources in ACPI, so for each state of a
> "master" device (in principle, there may be more states of it than
> just two) there would be a list of "dependent" intput devices that
> need to be inhibited when the "master" device goes into that state.

So a big part of the reason to punt the decision on which input
devices to enable this auto-inhibit is that we don't really have
information about those relationsships / device-links you are
suggesting here.  libinput is already doing inhibiting inside
userspace for e.g. the tablet-mode switch but it relies on heuristics
+ quirk tables to decide which keyboards should be inhibited and which
not.

E.g. for a 360 degree hinges 2-in-1 we want to disable the builtin
keyboard, when folded into in tablet mode, but not any external ones.

Mostly the builtin kbd will be PS2 but I have one such 2-in-1 here
in my home office with a USB kbd ...

In general of the master devices there will be only 1, there will be
only 1 lid switch and only 1 tablet-mode switch. So my idea with the
auto_inhibit_ev_sw_mask, is for it to be a per input-device setting.

So using your terms, all input devices with the (1 << SW_LID) bit
set in their auto_inhibit_ev_sw_mask will be dependents of the
(master) device which actually is reporting the SW_LID bit.

The idea here is for this to work the same as how the rfkill code
from net/rfkill/input.c works, except instead of binding e.g.
KEY_WLAN to toggling the sw-state of rfkill devices with a type
of RFKILL_TYPE_WLAN. This will bind SW_LID to inhibiting input
devices with the SW_LID bit set in their auto_inhibit_ev_sw_mask.

Regards,

Hans

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