PM: update docs for writing .../power/state

Updates to match current code:

 - Make writes to the /sys/devices/.../power/state files fail cleanly
   if the device requires the irqs-off call variants.

 - Fix comments describing the /sys/devices/.../power/state file writes
   to match the code; the last several releases have invalidated the
   previous text.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 19 insertions, 10 deletions

diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
index 40d7242a07c1..e55b3c2779e9 100644
--- a/drivers/base/power/sysfs.c
+++ b/drivers/base/power/sysfs.c
@@ -11,18 +11,23 @@
  *      state - Control current power state of device
  *
  *      show() returns the current power state of the device. '0' indicates
- *      the device is on. Other values (1-3) indicate the device is in a low
+ *      the device is on. Other values (2) indicate the device is in some low
  *      power state.
  *
- *      store() sets the current power state, which is an integer value
- *      between 0-3. If the device is on ('0'), and the value written is
- *      greater than 0, then the device is placed directly into the low-power
- *      state (via its driver's ->suspend() method).
- *      If the device is currently in a low-power state, and the value is 0,
- *      the device is powered back on (via the ->resume() method).
- *      If the device is in a low-power state, and a different low-power state
- *      is requested, the device is first resumed, then suspended into the new
- *      low-power state.
+ *      store() sets the current power state, which is an integer valued
+ *      0, 2, or 3.  Devices with bus.suspend_late(), or bus.resume_early()
+ *      methods fail this operation; those methods couldn't be called.
+ *      Otherwise,
+ *
+ *      - If the recorded dev->power.power_state.event matches the
+ *        target value, nothing is done.
+ *      - If the recorded event code is nonzero, the device is reactivated
+ *        by calling bus.resume() and/or class.resume().
+ *      - If the target value is nonzero, the device is suspended by
+ *        calling class.suspend() and/or bus.suspend() with event code
+ *        PM_EVENT_SUSPEND.
+ *
+ *      This mechanism is DEPRECATED and should only be used for testing.
  */
 
 static ssize_t state_show(struct device * dev, struct device_attribute *attr, char * buf)
@@ -38,6 +43,10 @@ static ssize_t state_store(struct device * dev, struct device_attribute *attr, c
         pm_message_t state;
         int error = -EINVAL;
 
+        /* disallow incomplete suspend sequences */
+        if (dev->bus && (dev->bus->suspend_late || dev->bus->resume_early))
+                return error;
+
         state.event = PM_EVENT_SUSPEND;
         /* Older apps expected to write "3" here - confused with PCI D3 */
         if ((n == 1) && !strcmp(buf, "3"))