How to prevent Linux from waking up due to USB devices

2016-03-26

最近換了一台工作機，但我發現在 Ubuntu 14.04.3 上，有時候會休眠失敗。 在失敗的時候，機器有 suspend 成功，但是過2秒後機器就會自動醒來。查看了 /var/log/kern.log, /var/log/syslog, /var/log/pm-suspend.log 沒有太異常的訊息。後來上網查了一下，這可能是有 BIOS 有問題或 device 不正常運作。

在 /proc/acpi/wakeup 中，列出了數種 wakeup event, 以下面的表來說，代表了機器開放了 EHC1, EHC2, PWRB, LID0 這幾種 wakeup event

RP06      S4    *disabled
PXSX      S4    *disabled
RP07      S4    *disabled
PXSX      S4    *disabled
EHC1      S0    *enabled   pci:0000:00:1d.0
EHC2      S4    *enabled  pci:0000:00:1a.0
PWRB      S4    *enabled   platform:PNP0C0C:00
LID0      S4    *enabled   platform:PNP0C0D:00

試著開關 wakeup trigger 來找出問題

# ignore XHC device wakeup event
echo "XHC" > /proc/acpi/wakeup
# try suspend, still failed

# ignore EHC1 device wakeup event
echo "EHC1" > /proc/acpi/wakeup
# try suspend, still failed

# ignore EHC1 device wakeup event
echo "EHC2" > /proc/acpi/wakeup
# try suspend. Bingo!! It suspend successfully!

發現只要關閉 EHC2 wakeup trigger, 機器就能正常 suspend。可以放罝一個 upstart script，讓每次開機時，都自動關閉 EHC2 wakeup trigger

# /etc/init/disable-EHC2.conf
start on started dbus
stop on stopping dbus

script
   sudo -u root sh -c "echo 'EHC2' > /proc/acpi/wakeup"
end script

Ref: - Ubuntu 14.04 wake up immediately after suspend - Ask Ubuntu - UnderstandingSuspend - Ubuntu Wiki - Power management/Suspend and hibernate - ArchWiki - acpitool(1) - Linux man page - Best practice to debug Linux* suspend/hibernate issues | 01.org

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