How to prevent Linux from waking up due to USB devices

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

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