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Diffstat (limited to 'Documentation/power/devices.txt')
| -rw-r--r-- | Documentation/power/devices.txt | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt index 57080cd..dd9b492 100644 --- a/Documentation/power/devices.txt +++ b/Documentation/power/devices.txt @@ -159,18 +159,18 @@ matter, and the kernel is responsible for keeping track of it. By contrast, whether or not a wakeup-capable device should issue wakeup events is a policy decision, and it is managed by user space through a sysfs attribute: the power/wakeup file. User space can write the strings "enabled" or "disabled" to -set or clear the should_wakeup flag, respectively. Reads from the file will -return the corresponding string if can_wakeup is true, but if can_wakeup is -false then reads will return an empty string, to indicate that the device -doesn't support wakeup events. (But even though the file appears empty, writes -will still affect the should_wakeup flag.) +set or clear the "should_wakeup" flag, respectively. This file is only present +for wakeup-capable devices (i.e. devices whose "can_wakeup" flags are set) +and is created (or removed) by device_set_wakeup_capable(). Reads from the +file will return the corresponding string. The device_may_wakeup() routine returns true only if both flags are set. -Drivers should check this routine when putting devices in a low-power state -during a system sleep transition, to see whether or not to enable the devices' -wakeup mechanisms. However for runtime power management, wakeup events should -be enabled whenever the device and driver both support them, regardless of the -should_wakeup flag. +This information is used by subsystems, like the PCI bus type code, to see +whether or not to enable the devices' wakeup mechanisms. If device wakeup +mechanisms are enabled or disabled directly by drivers, they also should use +device_may_wakeup() to decide what to do during a system sleep transition. +However for runtime power management, wakeup events should be enabled whenever +the device and driver both support them, regardless of the should_wakeup flag. /sys/devices/.../power/control files |