PM: Add facility for advanced testing of async suspend/resume

Add configuration switch CONFIG_PM_ADVANCED_DEBUG for compiling in
extra PM debugging/testing code allowing one to access some
PM-related attributes of devices from the user space via sysfs.

If CONFIG_PM_ADVANCED_DEBUG is set, add sysfs attribute power/async
for every device allowing the user space to access the device's
power.async_suspend flag and modify it, if desired.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

4 files changed, 100 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
index 431bfd7e65c7..6123c523bfd7 100644
--- a/Documentation/ABI/testing/sysfs-devices-power
+++ b/Documentation/ABI/testing/sysfs-devices-power
@@ -51,3 +51,29 @@ Description:
                 drivers.  Changing this attribute to "on" prevents the driver
                 from power managing the device at run time.  Doing that while
                 the device is suspended causes it to be woken up.
+
+What:           /sys/devices/.../power/async
+Date:           January 2009
+Contact:        Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+                The /sys/devices/.../async attribute allows the user space to
+                enable or diasble the device's suspend and resume callbacks to
+                be executed asynchronously (ie. in separate threads, in parallel
+                with the main suspend/resume thread) during system-wide power
+                transitions (eg. suspend to RAM, hibernation).
+
+                All devices have one of the following two values for the
+                power/async file:
+
+                + "enabled\n" to permit the asynchronous suspend/resume;
+                + "disabled\n" to forbid it;
+
+                The value of this attribute may be changed by writing either
+                "enabled", or "disabled" to it.
+
+                It generally is unsafe to permit the asynchronous suspend/resume
+                of a device unless it is certain that all of the PM dependencies
+                of the device are known to the PM core.  However, for some
+                devices this attribute is set to "enabled" by bus type code or
+                device drivers and in that cases it should be safe to leave the
+                default value.
diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
index c011ff15632c..86fd9373447e 100644
--- a/drivers/base/power/sysfs.c
+++ b/drivers/base/power/sysfs.c
@@ -54,6 +54,24 @@
  *      wakeup events internally (unless they are disabled), keeping
  *      their hardware in low power modes whenever they're unused.  This
  *      saves runtime power, without requiring system-wide sleep states.
+ *
+ *      async - Report/change current async suspend setting for the device
+ *
+ *      Asynchronous suspend and resume of the device during system-wide power
+ *      state transitions can be enabled by writing "enabled" to this file.
+ *      Analogously, if "disabled" is written to this file, the device will be
+ *      suspended and resumed synchronously.
+ *
+ *      All devices have one of the following two values for power/async:
+ *
+ *       + "enabled\n" to permit the asynchronous suspend/resume of the device;
+ *       + "disabled\n" to forbid it;
+ *
+ *      NOTE: It generally is unsafe to permit the asynchronous suspend/resume
+ *      of a device unless it is certain that all of the PM dependencies of the
+ *      device are known to the PM core.  However, for some devices this
+ *      attribute is set to "enabled" by bus type code or device drivers and in
+ *      that cases it should be safe to leave the default value.
  */
 
 static const char enabled[] = "enabled";
@@ -125,12 +143,43 @@ wake_store(struct device * dev, struct device_attribute *attr,
 
 static DEVICE_ATTR(wakeup, 0644, wake_show, wake_store);
 
+#ifdef CONFIG_PM_SLEEP_ADVANCED_DEBUG
+static ssize_t async_show(struct device *dev, struct device_attribute *attr,
+                          char *buf)
+{
+        return sprintf(buf, "%s\n",
+                        device_async_suspend_enabled(dev) ? enabled : disabled);
+}
+
+static ssize_t async_store(struct device *dev, struct device_attribute *attr,
+                           const char *buf, size_t n)
+{
+        char *cp;
+        int len = n;
+
+        cp = memchr(buf, '\n', n);
+        if (cp)
+                len = cp - buf;
+        if (len == sizeof enabled - 1 && strncmp(buf, enabled, len) == 0)
+                device_enable_async_suspend(dev);
+        else if (len == sizeof disabled - 1 && strncmp(buf, disabled, len) == 0)
+                device_disable_async_suspend(dev);
+        else
+                return -EINVAL;
+        return n;
+}
+
+static DEVICE_ATTR(async, 0644, async_show, async_store);
+#endif /* CONFIG_PM_SLEEP_ADVANCED_DEBUG */
 
 static struct attribute * power_attrs[] = {
 #ifdef CONFIG_PM_RUNTIME
         &dev_attr_control.attr,
 #endif
         &dev_attr_wakeup.attr,
+#ifdef CONFIG_PM_SLEEP_ADVANCED_DEBUG
+        &dev_attr_async.attr,
+#endif
         NULL,
 };
 static struct attribute_group pm_attr_group = {
diff --git a/include/linux/device.h b/include/linux/device.h
index 70adc5f3f50a..b30527db3ac0 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -478,6 +478,17 @@ static inline void device_enable_async_suspend(struct device *dev)
                 dev->power.async_suspend = true;
 }
 
+static inline void device_disable_async_suspend(struct device *dev)
+{
+        if (dev->power.status == DPM_ON)
+                dev->power.async_suspend = false;
+}
+
+static inline bool device_async_suspend_enabled(struct device *dev)
+{
+        return !!dev->power.async_suspend;
+}
+
 void driver_init(void);
 
 /*
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 4c9cffcf69c7..5c36ea9d55d2 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -27,6 +27,15 @@ config PM_DEBUG
         code. This is helpful when debugging and reporting PM bugs, like
         suspend support.
 
+config PM_ADVANCED_DEBUG
+        bool "Extra PM attributes in sysfs for low-level debugging/testing"
+        depends on PM_DEBUG
+        default n
+        ---help---
+        Add extra sysfs attributes allowing one to access some Power Management
+        fields of device objects from user space.  If you are not a kernel
+        developer interested in debugging/testing Power Management, say "no".
+
 config PM_VERBOSE
         bool "Verbose Power Management debugging"
         depends on PM_DEBUG
@@ -85,6 +94,11 @@ config PM_SLEEP
         depends on SUSPEND || HIBERNATION || XEN_SAVE_RESTORE
         default y
 
+config PM_SLEEP_ADVANCED_DEBUG
+        bool
+        depends on PM_ADVANCED_DEBUG
+        default n
+
 config SUSPEND
         bool "Suspend to RAM and standby"
         depends on PM && ARCH_SUSPEND_POSSIBLE