FreeBSD/src ebe71cb (r343157)sys/dev/atkbdc psm.c atkbdc.c

MFC r340912,r340913:

psm(4): Revert r328640 and add minimal support for active AUX port
        multiplexers

Active PS/2 multiplexing is a method for attaching up to four PS/2
pointing devices to a computer. Enabling of multiplexed mode allows
commands to be directed to individual devices using routing prefixes.
Multiplexed mode reports input with each byte tagged to identify
its source. This method differs from one currently supported by psm(4)
where so called guest device (trackpoint) is attached to special
interface located on the host device (touchpad) and latter performs
guest protocol conversion to special encapsulation packet format.

At present time active PS/2 multiplexing is used in some models of
HP laptops e.g. EliteBook 8560w, 9470m. Enabling of absolute operation
mode on such touchpads is connected with following problems:
1. Touchpad's port priority is lower than trackpoint's. That blocks
   information queries thus prevents touchpad detection and configuration.
2. Touchpad and trackpoint have different protocol packet sizes and
   sync bytes.

As PS/2 usage is on decline only minimal possible set of changes to
support Synaptics touchpad and generic mouses is implemented.
Active multiplexing mode is enabled only at probe stage to scan through
attached PS/2 devices to query and configure Synaptics touchpad.
After touchpad has been configured, mux is switched back to legacy
(hidden multiplexing) mode to perform normal interrupt-driven input
data processing. Overflow bit values rather than tags are used to
separate packets produced by different devices. Switching back to
legacy mode allows to avoid psm(4) and atkbd(4) rework to support
4 instances of mouse driver.

Note: While in hidden multiplexing mode KBC does some editing of the
packet stream. It remembers the button bits from the last packet
received from each device, and replaces the button bits of every
packet with the logical OR of all devices’ most recent button bits.
This sort of button crosstalk results in spurious button events
which are inhibitted with various tricks. E.g. trackpoint middle
button events are suppressed while trackpad surface is touched and
touchpad left and right button events are suppressed if corresponding
trackpoint buttons are pressed.

PR:             231058
Reported by:    Michael Figiel <mifigiel at gmail.com>
Tested by:      Michael Figiel <mifigiel at gmail.com>
DeltaFile
+185-60sys/dev/atkbdc/psm.c
+82-1sys/dev/atkbdc/atkbdc.c
+11-0sys/dev/atkbdc/atkbdcreg.h
+278-613 files

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