Merge branch 'drm-patches' of master.kernel.org:/pub/scm/linux/kernel/git/airlied...

[linux-drm-fsl-dcu.git] / Documentation / power / interface.txt

diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt
index 4117802af0f8ce560316d557045566a5f0ea8494..fd5192a8fa8abebd12fe86aefd99404978d88f34 100644 (file)
--- a/Documentation/power/interface.txt
+++ b/Documentation/power/interface.txt
@@ -18,28 +18,34 @@ states.
 
 
 /sys/power/disk controls the operating mode of the suspend-to-disk
-mechanism. Suspend-to-disk can be handled in several ways. The
-greatest distinction is who writes memory to disk - the firmware or
-the kernel. If the firmware does it, we assume that it also handles
-suspending the system. 
-
-If the kernel does it, then we have three options for putting the system
-to sleep - using the platform driver (e.g. ACPI or other PM
-registers), powering off the system or rebooting the system (for
-testing). The system will support either 'firmware' or 'platform', and
-that is known a priori. But, the user may choose 'shutdown' or
-'reboot' as alternatives. 
-
-Reading from this file will display what the mode is currently set
-to. Writing to this file will accept one of
-
-       'firmware'
-       'platform'
+mechanism. Suspend-to-disk can be handled in several ways. We have a
+few options for putting the system to sleep - using the platform driver
+(e.g. ACPI or other pm_ops), powering off the system or rebooting the
+system (for testing).
+
+Additionally, /sys/power/disk can be used to turn on one of the two testing
+modes of the suspend-to-disk mechanism: 'testproc' or 'test'.  If the
+suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to
+/sys/power/state will cause the kernel to disable nonboot CPUs and freeze
+tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs.  If it is
+in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel
+to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait
+for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs.  Then,
+we are able to look in the log messages and work out, for example, which code
+is being slow and which device drivers are misbehaving.
+
+Reading from this file will display all supported modes and the currently
+selected one in brackets, for example
+
+       [shutdown] reboot test testproc
+
+Writing to this file will accept one of
+
+       'platform' (only if the platform supports it)
        'shutdown'
        'reboot'
-
-It will only change to 'firmware' or 'platform' if the system supports
-it. 
+       'testproc'
+       'test'
 
 /sys/power/image_size controls the size of the image created by
 the suspend-to-disk mechanism.  It can be written a string
@@ -52,3 +58,18 @@ suspend image will be as small as possible.
 
 Reading from this file will display the current image size limit, which
 is set to 500 MB by default.
+
+/sys/power/pm_trace controls the code which saves the last PM event point in
+the RTC across reboots, so that you can debug a machine that just hangs
+during suspend (or more commonly, during resume).  Namely, the RTC is only
+used to save the last PM event point if this file contains '1'.  Initially it
+contains '0' which may be changed to '1' by writing a string representing a
+nonzero integer into it.
+
+To use this debugging feature you should attempt to suspend the machine, then
+reboot it and run
+
+       dmesg -s 1000000 | grep 'hash matches'
+
+CAUTION: Using it will cause your machine's real-time (CMOS) clock to be
+set to a random invalid time after a resume.