coreboot

Hit one of these on a sibling ADL-N board with the same IT8625E Super-I/O. This also looks like the "broken IRQ 9" in #631, and I think it explains why the GPIO patch there did not help: it is not GPIO.

IRQ9 / SCI storm. topton/adl/devicetree.cb declares only the IT8625E COM1 LDN, not the Environment Controller / HWM LDN (2e.4). coreboot auto-creates an undeclared Super-I/O LDN as enabled (device.c __alloc_dev sets enabled=1) and activates it, but with no irq 0x70 in the devicetree it never writes the HWM's IRQ register, so that register keeps its power-on default = IRQ9 = the SCI line. On a fanless box the empty CPU-fan header makes the HWM raise a permanent fan-fault, which then storms IRQ9 over the eSPI virtual wire with no GPE/PM1 status to ack, so the kernel masks it ("nobody cared"). The stock firmware keeps the HWM off the SCI.

Quick check on the running board:

superiotool -d # LDN 0x04 (EC): is it active, and is reg 0x70 = 09?
Fix is to declare the HWM LDN and force no IRQ (keeps the sensors, off the SCI):

device pnp 2e.4 on # Environment Controller (HWM)
io 0x60 = 0xa30 # take the bases from your superiotool -d
io 0x62 = 0xa20
irq 0x70 = 0x00 # HWM off IRQ9 (= the SCI), matches stock
end

IRQ4 / UART0 storm is separate and is not a coreboot bug. coreboot hands the 3f8 UART to the OS with all interrupts disabled (uart8250io.c writes IER=0). FreeBSD's ns8250 then enables modem-status interrupts (IER_EMSC) by default; on the "Cisco-style" RJ45 console the RS232 handshake inputs (CTS/DSR/DCD/RI) are unconnected and float, so their status-change deltas storm IRQ4. hint.uart.0.disabled="1" is a correct fix if you do not use that port. To keep the serial console but kill the storm, drop only modem-status interrupts:

hint.uart.0.ier_rxbits="0x05" # IER_ERLS|IER_ERXRDY, no IER_EMSC
(The IT8625E serial reg 0xF0=1 = IRQ-sharing mode is not implicated; the non-storming sibling uses the same value.)

Re the gpio.patch from ellyq in #631: on my sibling ADL-N board the same IRQ 9 turned out to be not GPIO but the IT8625E HWM on its default SCI IRQ, so a GPIO-only change would not settle it on topton either.

Pushed the fix to Gerrit (in the shared topton/adl devicetree, so it covers
the x2e_n150):

https://review.coreboot.org/c/coreboot/+/94028

Could you build master with it and confirm the IRQ 9 storm is gone on
FreeBSD/OPNsense? If it holds up I'll note it here.

Sebastian Müller wrote in #note-3:

Pushed the fix to Gerrit (in the shared topton/adl devicetree, so it covers
the x2e_n150):

https://review.coreboot.org/c/coreboot/+/94028

Could you build master with it and confirm the IRQ 9 storm is gone on
FreeBSD/OPNsense? If it holds up I'll note it here.

Thanks, Sebastian. The initial test with the same change already improved the system significantly, and the IRQ9 storm appears to be gone. I am now building and testing your exact Gerrit patch, and I will report back once I complete the remaining checks with superiotool, dmesg, and vmstat -i.

Confirmed on the x2e_n150 after flashing the build with Gerrit change 94028. OPNsense boots normally and vmstat -i shows no IRQ9/SCI storm.

Separately, hint.uart.0.ier_rxbits="0x05" reduced the FreeBSD UART0 storm from about 9,956 interrupts/s (2,027,625 total) to about 21 interrupts/s (735 total).