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Subject[PATCH 4/8] PM: Add facility for advanced testing of async suspend/resume
Date
From: Rafael J. Wysocki <rjw@sisk.pl>

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>
---
Documentation/ABI/testing/sysfs-devices-power | 26 +++++++++++++
drivers/base/power/sysfs.c | 49 ++++++++++++++++++++++++++
include/linux/device.h | 11 +++++
kernel/power/Kconfig | 14 +++++++
4 files changed, 100 insertions(+)
Index: linux-2.6/drivers/base/power/sysfs.c
===================================================================
--- linux-2.6.orig/drivers/base/power/sysfs.c
+++ linux-2.6/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 d

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 = {
Index: linux-2.6/include/linux/device.h
===================================================================
--- linux-2.6.orig/include/linux/device.h
+++ linux-2.6/include/linux/device.h
@@ -478,6 +478,17 @@ static inline void device_enable_async_s
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);

/*
Index: linux-2.6/kernel/power/Kconfig
===================================================================
--- linux-2.6.orig/kernel/power/Kconfig
+++ linux-2.6/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
Index: linux-2.6/Documentation/ABI/testing/sysfs-devices-power
===================================================================
--- linux-2.6.orig/Documentation/ABI/testing/sysfs-devices-power
+++ linux-2.6/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.


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