The touchpad driver crashed the ASUS TUF A15 at boot. Its thread runs the
firmware's AML -- _DSM, _PS0, _CRS -- through uACPI at -O0, on an 8 KB
kernel stack, and kernel stacks are one array: running off the end lands
in the next thread's stack, and the machine dies a moment later in some
other code. The thread now runs on a 64 KB stack of its own, through
SCFF's call_on_stack().
And a crashed laptop sat with its fans up until somebody held the power
button, since the other processors keep running. On an ordinary boot the
PSOGM now says it will power off, and does, after three minutes: SLP_TYP
from \_S5, read at boot, written straight to PM1 control with no AML, which
could sleep or wait on a lock a dead processor holds. A verbose boot keeps
the screen up for ever.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
The ASUS TUF A15 freezes at the default resolution shortly after the
loader hands over -- screen dark, Caps Lock dead -- and it is the only
machine here with an I2C-HID touchpad, which the driver added in the same
release now probes at boot. "Touchpad driver: on/off" in the F8 menu
answers whether it is the cause on the machine itself, through a new
SCHBOOT_OFF_FLAGS byte the kernel checks before starting the driver.
A verbose boot now prints each step of the probe before taking it, so if it
is the cause, the last line on the screen says which step.
Also: S in the menu wrapped at five entries whatever the count.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
A laptop's touchpad is on the chipset's I2C bus, found only through ACPI
(PNP0C50 / ACPI0C50), and SchOS had no I2C at all, so the touchpad of
every recent laptop did nothing.
kernel/acpi/i2c_hid.c drives the DesignWare I2C controller every x86
chipset uses (AMDI0010 on Ryzen) by polling, speaks HID over I2C to the
device the _DSM points at, and feeds the reports through the USB HID
parser. On AMD the interrupt pin's level is read every tick, so a report
is read exactly when one is waiting; elsewhere the input register is polled.
The touchpad is driven in mouse mode, which it starts in after a reset:
motion, clicks and taps become /dev/input/event1 like any mouse. The HID
parser now prefers a descriptor's relative pointer over an absolute one
for this, and takes descriptors from transports other than USB.
Untested on hardware: QEMU emulates no I2C touchpad.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
