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networking: recover the WWAN modem after a cold boot

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After a cold boot the EM160R-GL often drops off the PCIe link 10-20s
after probe ("Unable to change power state from D3cold to D0", config
space reads all-ones) and never brings up its wwan ports. Until now
only a hibernate/resume cycle brought it back.

An ACPI _RST through the PCI reset attribute does the same at runtime.
The rescan after it catches the firmware mid-boot, under the generic
Qualcomm ID 17cb:0304, which has no FCC unlock script, so ModemManager
fails with "Couldn't set operating mode". A second rescan once the
firmware is up gets 1eac:100d back and the modem enables normally.

The service does nothing if wwan ports show up within 60s of boot.
The recovery sequence was verified by hand on 7.2.11; the service has
not yet run it on a real cold boot.

Assisted-by: Claude:opus-5-5
This commit is contained in:
Sergei Poljanski 2026-10-20 20:37:11 +04:00
commit 285933d22c
Signed by: asxpi
GPG key ID: 4F8851660FA4121B
1 changed files with 47 additions and 0 deletions
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47
modules/networking.nix
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@ -56,6 +56,53 @@
ACTION=="add", SUBSYSTEM=="mhi", KERNEL=="mhi[0-9]*", ATTR{power/wakeup}="disabled" ACTION=="add", SUBSYSTEM=="mhi", KERNEL=="mhi[0-9]*", ATTR{power/wakeup}="disabled"
''; '';
# EM160R-GL cold-boot recovery.
# Why: after a cold boot the modem often drops off the PCIe link ~10-20s
# after probe ("Unable to change power state from D3cold to D0", config
# space reads all-ones) and never brings up its wwan ports; only a platform
# power cycle (hibernate/resume) recovered it. An ACPI _RST via the PCI
# reset attribute does the same live. The first rescan catches the firmware
# mid-boot with the generic Qualcomm ID 17cb:0304, which has no FCC unlock
# script (ModemManager then fails with "Couldn't set operating mode"), so
# once the firmware is up, re-enumerate again to get 1eac:100d back.
# Verified live 2026-10-20 on kernel 7.2.11.
systemd.services.wwan-coldboot-recover = {
description = "Recover EM160R-GL WWAN modem dead after cold boot";
wantedBy = [ "multi-user.target" ];
after = [ "systemd-udev-trigger.service" ];
serviceConfig.Type = "exec";
script = ''
dev=
for d in /sys/bus/pci/devices/*; do
[ "$(cat $d/vendor)" = 0x1eac ] && [ "$(cat $d/device)" = 0x100d ] && dev=$d
done
[ -n "$dev" ] || { echo "modem not found"; exit 0; }
addr=$(basename $dev)
wait_ports() {
for _ in $(seq "$1"); do [ -e /sys/class/wwan/wwan0 ] && return 0; sleep 1; done
return 1
}
rescan() {
echo 1 > /sys/bus/pci/devices/$addr/remove
echo 1 > /sys/bus/pci/rescan
}
wait_ports 60 && { echo "modem up, nothing to do"; exit 0; }
echo "no wwan ports after 60s, resetting $addr via ACPI _RST"
[ -e $dev/driver ] && echo $addr > $dev/driver/unbind
echo acpi > $dev/reset_method
echo 1 > $dev/reset
rescan
wait_ports 90 || { echo "modem still down after reset"; exit 1; }
sleep 30
rescan
wait_ports 60 || { echo "modem lost after re-enumeration"; exit 1; }
echo "modem recovered as $(cat /sys/bus/pci/devices/$addr/vendor):$(cat /sys/bus/pci/devices/$addr/device)"
'';
};
# Ensure ModemManager starts before NetworkManager # Ensure ModemManager starts before NetworkManager
systemd.services.ModemManager = { systemd.services.ModemManager = {
wantedBy = [ "multi-user.target" ]; wantedBy = [ "multi-user.target" ];