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PM: Do not create wakeup sysfs files for devices that cannot wake up

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Currently, wakeup sysfs attributes are created for all devices,
regardless of whether or not they are wakeup-capable.  This is
excessive and complicates wakeup device identification from user
space (i.e. to identify wakeup-capable devices user space has to read
/sys/devices/.../power/wakeup for all devices and see if they are not
empty).

Fix this issue by avoiding to create wakeup sysfs files for devices
that cannot wake up the system from sleep states (i.e. whose
power.can_wakeup flags are unset during registration) and modify
device_set_wakeup_capable() so that it adds (or removes) the relevant
sysfs attributes if a device's wakeup capability status is changed.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
This commit is contained in:
Rafael J. Wysocki
2011-02-08 23:26:02 +01:00
parent 4681b17154
commit cb8f51bdad
7 changed files with 121 additions and 69 deletions
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20
Documentation/power/devices.txt
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@@ -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