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

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>

2 files changed, 20 insertions, 20 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
index 7628cd1bc36a..8ffbc25376a0 100644
--- a/Documentation/ABI/testing/sysfs-devices-power
+++ b/Documentation/ABI/testing/sysfs-devices-power
@@ -29,9 +29,8 @@ Description:
                 "disabled" to it.
 
                 For the devices that are not capable of generating system wakeup
-                events this file contains "\n".  In that cases the user space
-                cannot modify the contents of this file and the device cannot be
-                enabled to wake up the system.
+                events this file is not present.  In that case the device cannot
+                be enabled to wake up the system from sleep states.
 
 What:           /sys/devices/.../power/control
 Date:           January 2009
@@ -85,7 +84,7 @@ Description:
                 The /sys/devices/.../wakeup_count attribute contains the number
                 of signaled wakeup events associated with the device.  This
                 attribute is read-only.  If the device is not enabled to wake up
-                the system from sleep states, this attribute is empty.
+                the system from sleep states, this attribute is not present.
 
 What:           /sys/devices/.../power/wakeup_active_count
 Date:           September 2010
@@ -95,7 +94,7 @@ Description:
                 number of times the processing of wakeup events associated with
                 the device was completed (at the kernel level).  This attribute
                 is read-only.  If the device is not enabled to wake up the
-                system from sleep states, this attribute is empty.
+                system from sleep states, this attribute is not present.
 
 What:           /sys/devices/.../power/wakeup_hit_count
 Date:           September 2010
@@ -105,7 +104,8 @@ Description:
                 number of times the processing of a wakeup event associated with
                 the device might prevent the system from entering a sleep state.
                 This attribute is read-only.  If the device is not enabled to
-                wake up the system from sleep states, this attribute is empty.
+                wake up the system from sleep states, this attribute is not
+                present.
 
 What:           /sys/devices/.../power/wakeup_active
 Date:           September 2010
@@ -115,7 +115,7 @@ Description:
                 or 0, depending on whether or not a wakeup event associated with
                 the device is being processed (1).  This attribute is read-only.
                 If the device is not enabled to wake up the system from sleep
-                states, this attribute is empty.
+                states, this attribute is not present.
 
 What:           /sys/devices/.../power/wakeup_total_time_ms
 Date:           September 2010
@@ -125,7 +125,7 @@ Description:
                 the total time of processing wakeup events associated with the
                 device, in milliseconds.  This attribute is read-only.  If the
                 device is not enabled to wake up the system from sleep states,
-                this attribute is empty.
+                this attribute is not present.
 
 What:           /sys/devices/.../power/wakeup_max_time_ms
 Date:           September 2010
@@ -135,7 +135,7 @@ Description:
                 the maximum time of processing a single wakeup event associated
                 with the device, in milliseconds.  This attribute is read-only.
                 If the device is not enabled to wake up the system from sleep
-                states, this attribute is empty.
+                states, this attribute is not present.
 
 What:           /sys/devices/.../power/wakeup_last_time_ms
 Date:           September 2010
@@ -146,7 +146,7 @@ Description:
                 signaling the last wakeup event associated with the device, in
                 milliseconds.  This attribute is read-only.  If the device is
                 not enabled to wake up the system from sleep states, this
-                attribute is empty.
+                attribute is not present.
 
 What:           /sys/devices/.../power/autosuspend_delay_ms
 Date:           September 2010
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index 57080cd74575..dd9b49251db3 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