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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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