Hi Huacai,
On Sun, 9 Aug 2026 at 12:16, Huacai Chen <[email protected]> wrote:
> You never answer me why in your test you should disable i8042 from V1
> until V4. In normal use we use a single kernel for both host and guest.
I owe you an apology: I did not actually understand your question. I
thought the commit message had already explained the reason (the
i8042_flush() panic), so I treated it as answered and never addressed
what you were really asking. Let me answer it directly now.
You are right that this is not just a selftest detail. i8042 is built on
every LoongArch kernel: arch/loongarch/Kconfig selects
ARCH_MIGHT_HAVE_PC_SERIO, and KEYBOARD_ATKBD and MOUSE_PS2 (both default
y) select SERIO_I8042 under it. So your "single kernel for host and
guest" point is correct -- a normal defconfig kernel has i8042 built in.
On the QEMU virtual machine there is no i8042, so PNP finds nothing and
i8042_pnp_init() falls back to probing the i8042 status and data
registers (I8042_STATUS_REG, I8042_DATA_REG) directly. On LoongArch those
registers are memory-mapped, and on the virtual machine they are not backed
by any device, so i8042_flush() takes a page fault and the kernel panics
before userspace. A normal LoongArch defconfig kernel booted as a QEMU
guest hits the same panic -- the "# CONFIG_SERIO_I8042 is not set" in
loongarch.conf is only a workaround to let the KHO selftest boot, not a
fix.
The real fix is separate from the KHO series: make i8042 bail out on
LoongArch when ACPI/PNP does not describe a controller, so the direct-port
fallback never runs. I have prepared that as a standalone patch -- the
relevant hunk is below -- and will send the full patch separately. The
selftest workaround can be dropped once it lands.
diff --git a/drivers/input/serio/i8042-acpipnpio.h
b/drivers/input/serio/i8042-acpipnpio.h
--- a/drivers/input/serio/i8042-acpipnpio.h
+++ b/drivers/input/serio/i8042-acpipnpio.h
@@ -1633,8 +1633,14 @@ static int __init i8042_pnp_init(void)
#else
pr_info("PNP: No PS/2 controller found.\n");
#if defined(__loongarch__)
- if (acpi_disabled == 0)
- return -ENODEV;
+ /*
+ * LoongArch legacy I/O ports are memory-mapped and are not
+ * safely probeable when no controller is present: a direct
+ * probe faults on the QEMU virtual machine and on any FDT-based
+ * boot. Do not fall back to probing them directly; if ACPI/PNP
+ * did not describe a controller, assume there is none.
+ */
+ return -ENODEV;
#else
if (x86_platform.legacy.i8042 !=
X86_LEGACY_I8042_EXPECTED_PRESENT)
Thanks,
George
