Recently userspace has started making more use of SW_TABLET_MODE
(when an input-dev reports this).

Specifically recent GNOME3 versions will:

1.  When SW_TABLET_MODE is reported and is reporting 0:
1.1 Disable accelerometer-based screen auto-rotation
1.2 Disable automatically showing the on-screen keyboard when a
    text-input field is focussed

2.  When SW_TABLET_MODE is reported and is reporting 1:
2.1 Ignore input-events from the builtin keyboard and touchpad
    (this is for 360° hinges style 2-in-1s where the keyboard and
     touchpads are accessible on the back of the tablet when folded
     into tablet-mode)

This means that claiming to support SW_TABLET_MODE when it does not
actually work / reports correct values has bad side-effects.

The check in the hp-wmi code which is used to decide if the input-dev
should claim SW_TABLET_MODE support, only checks if the
HPWMI_HARDWARE_QUERY is supported. It does *not* check if the hardware
actually is capable of reporting SW_TABLET_MODE.

This leads to the hp-wmi input-dev claiming SW_TABLET_MODE support,
while in reality it will always report 0 as SW_TABLET_MODE value.
This has been seen on a "HP ENVY x360 Convertible 15-cp0xxx" and
this likely is the case on a whole lot of other HP models.

This problem causes both auto-rotation and on-screen keyboard
support to not work on affected x360 models.

There is no easy fix for this, but since userspace expects
SW_TABLET_MODE reporting to be reliable when advertised it is
better to not claim/report SW_TABLET_MODE support at all, then
to claim to support it while it does not work.

To avoid the mentioned problems, add a new enable_tablet_mode_sw
module-parameter which defaults to false.

Note I've made this an int using the standard -1=auto, 0=off, 1=on
triplett, with the hope that in the future we can come up with a
better way to detect SW_TABLET_MODE support. ATM the default
auto option just does the same as off.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1918255
Cc: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Mark Gross <mgross@linux.intel.com>
Link: https://lore.kernel.org/r/20210120124941.73409-1-hdegoede@redhat.com