kern/60651: pms(4) misdetects Perixx PS/2 wheel mouse as 5-button protocol

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>Number:         60651
>Category:       kern
>Synopsis:       pms(4) misdetects Perixx PS/2 wheel mouse as 5-button protocol
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Aug 26 18:45:00 +0000 2026
>Originator:     luis
>Release:        NetBSD 11.0
>Organization:
	
>Environment:
NetBSD ambox 11.0 NetBSD 11.0 (GENERIC) #0: Thu Jul 30 15:23:12 UTC 2026 mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64

Hardware:
- x86_64/amd64 PC
- Perixx PS/2 mouse
- Directly connected to the motherboard's PS/2 mouse port
- Three physical buttons: left, middle/wheel, right
- Scroll wheel

The same physical mouse works correctly under Windows, Linux,
FreeBSD, and OpenBSD.

>Description:
The NetBSD 11.0 pms(4) driver incorrectly selects the
PMS_SCROLL5 protocol for this Perixx PS/2 mouse.

With the GENERIC kernel, the mouse is detected as:

pms0 at pckbc1 (aux slot)
wsmouse0 at pms0 mux 0

The mouse behaves incorrectly under X. Moving the mouse without
clicking any buttons or using the wheel generates spurious mouse
wheel/button events. This results in the cursor moving erratically
and applications receiving unintended input.

The problem is not limited to Xorg. Reading /dev/wsmouse0 directly
while moving the mouse shows WSCONS_EVENT_MOUSE_DELTA_Z events
and mouse button events even though no buttons or wheel are being
operated.

The relevant wscons event definitions are:

WSCONS_EVENT_MOUSE_UP        4
WSCONS_EVENT_MOUSE_DOWN      5
WSCONS_EVENT_MOUSE_DELTA_X   6
WSCONS_EVENT_MOUSE_DELTA_Y   7
WSCONS_EVENT_MOUSE_DELTA_Z   10

I built a diagnostic NetBSD 11.0 kernel with PMSDEBUG enabled.

With the unmodified pms driver, the kernel reports:

pms_protocol: found mouse protocol 3
pms_enable: using scroll wheel (5 buttons) protocol

The relevant pms.c code is:

static const enum pms_type tries[] = {
        PMS_SCROLL5, PMS_SCROLL3, PMS_STANDARD, PMS_UNKNOWN
};

The protocol table contains:

{ { 200, 100, 80 }, 3, "scroll wheel (3 buttons)" },
{ { 200, 200, 80 }, 4, "scroll wheel (5 buttons)" },

The driver therefore probes PMS_SCROLL5 first and accepts it
when the mouse responds with device ID 4.

>How-To-Repeat:
1. Connect the Perixx PS/2 mouse directly to a PS/2 mouse port.
2. Boot NetBSD 11.0 GENERIC.
3. Start X.
4. Run:

   xinput test Mouse0

5. Move the mouse without clicking or scrolling.

Spurious button 4/5 events are generated.

The problem can also be reproduced below X by stopping X and
reading /dev/wsmouse0 directly. The raw event stream contains
WSCONS_EVENT_MOUSE_DELTA_Z and mouse button events while only
moving the mouse.

>Fix:
As a diagnostic experiment, I changed the protocol probe order
in sys/dev/pckbport/pms.c from:

static const enum pms_type tries[] = {
        PMS_SCROLL5, PMS_SCROLL3, PMS_STANDARD, PMS_UNKNOWN
};

to:

static const enum pms_type tries[] = {
        PMS_SCROLL3, PMS_STANDARD, PMS_UNKNOWN
};

After rebuilding and booting the modified kernel, the driver
reports:

pms_protocol: found mouse protocol 2
pms_enable: using scroll wheel (3 buttons) protocol

The mouse then works correctly. Moving the mouse no longer
generates spurious wheel or button events.

The exact change is:

--- sys/dev/pckbport/pms.c.orig
+++ sys/dev/pckbport/pms.c
@@ -65,7 +65,7 @@
 static const enum pms_type tries[] = {
-       PMS_SCROLL5, PMS_SCROLL3, PMS_STANDARD, PMS_UNKNOWN
+       PMS_SCROLL3, PMS_STANDARD, PMS_UNKNOWN
 };

This workaround has been verified with a rebuilt NetBSD 11.0
kernel.

I am not certain why the mouse responds to the PMS_SCROLL5
identification sequence or whether the protocol negotiation
should reject that response. However, forcing PMS_SCROLL3 makes
the mouse operate correctly.

This mouse is a Perixx PS/2 mouse with three physical buttons
(left, middle/wheel, right) and a scroll wheel. It works correctly
with Windows, Linux, FreeBSD and OpenBSD.