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authorAnton Vorontsov <cbouatmailru@gmail.com>2012-01-04 09:09:35 +0400
committerAnton Vorontsov <cbouatmailru@gmail.com>2012-01-04 09:09:35 +0400
commit251f39fe42dae863bd24e30864e6b66076ba076d (patch)
treec804944bc17f3836d19cc8b5bc611dd1fb0ea915 /Documentation/power
parent9b8872273af6983b246252a6508fa7cf34c69d6e (diff)
parent35b4c01e29bdd9632dabf9784ed3486333f00427 (diff)
downloadlinux-251f39fe42dae863bd24e30864e6b66076ba076d.tar.gz
Merge branch 'power-supply-scope' of git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen
Diffstat (limited to 'Documentation/power')
-rw-r--r--Documentation/power/00-INDEX2
-rw-r--r--Documentation/power/basic-pm-debugging.txt26
-rw-r--r--Documentation/power/devices.txt8
-rw-r--r--Documentation/power/freezing-of-tasks.txt8
-rw-r--r--Documentation/power/pm_qos_interface.txt92
-rw-r--r--Documentation/power/regulator/machine.txt19
-rw-r--r--Documentation/power/runtime_pm.txt31
-rw-r--r--Documentation/power/suspend-and-cpuhotplug.txt275
-rw-r--r--Documentation/power/userland-swsusp.txt3
9 files changed, 435 insertions, 29 deletions
diff --git a/Documentation/power/00-INDEX b/Documentation/power/00-INDEX
index 45e9d4a9128..a4d682f5423 100644
--- a/Documentation/power/00-INDEX
+++ b/Documentation/power/00-INDEX
@@ -26,6 +26,8 @@ s2ram.txt
- How to get suspend to ram working (and debug it when it isn't)
states.txt
- System power management states
+suspend-and-cpuhotplug.txt
+ - Explains the interaction between Suspend-to-RAM (S3) and CPU hotplug
swsusp-and-swap-files.txt
- Using swap files with software suspend (to disk)
swsusp-dmcrypt.txt
diff --git a/Documentation/power/basic-pm-debugging.txt b/Documentation/power/basic-pm-debugging.txt
index ddd78172ef7..40a4c65f380 100644
--- a/Documentation/power/basic-pm-debugging.txt
+++ b/Documentation/power/basic-pm-debugging.txt
@@ -173,7 +173,7 @@ kernel messages using the serial console. This may provide you with some
information about the reasons of the suspend (resume) failure. Alternatively,
it may be possible to use a FireWire port for debugging with firescope
(ftp://ftp.firstfloor.org/pub/ak/firescope/). On x86 it is also possible to
-use the PM_TRACE mechanism documented in Documentation/s2ram.txt .
+use the PM_TRACE mechanism documented in Documentation/power/s2ram.txt .
2. Testing suspend to RAM (STR)
@@ -201,3 +201,27 @@ case, you may be able to search for failing drivers by following the procedure
analogous to the one described in section 1. If you find some failing drivers,
you will have to unload them every time before an STR transition (ie. before
you run s2ram), and please report the problems with them.
+
+There is a debugfs entry which shows the suspend to RAM statistics. Here is an
+example of its output.
+ # mount -t debugfs none /sys/kernel/debug
+ # cat /sys/kernel/debug/suspend_stats
+ success: 20
+ fail: 5
+ failed_freeze: 0
+ failed_prepare: 0
+ failed_suspend: 5
+ failed_suspend_noirq: 0
+ failed_resume: 0
+ failed_resume_noirq: 0
+ failures:
+ last_failed_dev: alarm
+ adc
+ last_failed_errno: -16
+ -16
+ last_failed_step: suspend
+ suspend
+Field success means the success number of suspend to RAM, and field fail means
+the failure number. Others are the failure number of different steps of suspend
+to RAM. suspend_stats just lists the last 2 failed devices, error number and
+failed step of suspend.
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index 3384d5996be..646a89e0c07 100644
--- a/Documentation/power/devices.txt
+++ b/Documentation/power/devices.txt
@@ -152,7 +152,9 @@ try to use its wakeup mechanism. device_set_wakeup_enable() affects this flag;
for the most part drivers should not change its value. The initial value of
should_wakeup is supposed to be false for the majority of devices; the major
exceptions are power buttons, keyboards, and Ethernet adapters whose WoL
-(wake-on-LAN) feature has been set up with ethtool.
+(wake-on-LAN) feature has been set up with ethtool. It should also default
+to true for devices that don't generate wakeup requests on their own but merely
+forward wakeup requests from one bus to another (like PCI bridges).
Whether or not a device is capable of issuing wakeup events is a hardware
matter, and the kernel is responsible for keeping track of it. By contrast,
@@ -279,10 +281,6 @@ When the system goes into the standby or memory sleep state, the phases are:
time.) Unlike the other suspend-related phases, during the prepare
phase the device tree is traversed top-down.
- In addition to that, if device drivers need to allocate additional
- memory to be able to hadle device suspend correctly, that should be
- done in the prepare phase.
-
After the prepare callback method returns, no new children may be
registered below the device. The method may also prepare the device or
driver in some way for the upcoming system power transition (for
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt
index 38b57248fd6..316c2ba187f 100644
--- a/Documentation/power/freezing-of-tasks.txt
+++ b/Documentation/power/freezing-of-tasks.txt
@@ -22,12 +22,12 @@ try_to_freeze_tasks() that sets TIF_FREEZE for all of the freezable tasks and
either wakes them up, if they are kernel threads, or sends fake signals to them,
if they are user space processes. A task that has TIF_FREEZE set, should react
to it by calling the function called refrigerator() (defined in
-kernel/power/process.c), which sets the task's PF_FROZEN flag, changes its state
+kernel/freezer.c), which sets the task's PF_FROZEN flag, changes its state
to TASK_UNINTERRUPTIBLE and makes it loop until PF_FROZEN is cleared for it.
Then, we say that the task is 'frozen' and therefore the set of functions
handling this mechanism is referred to as 'the freezer' (these functions are
-defined in kernel/power/process.c and include/linux/freezer.h). User space
-processes are generally frozen before kernel threads.
+defined in kernel/power/process.c, kernel/freezer.c & include/linux/freezer.h).
+User space processes are generally frozen before kernel threads.
It is not recommended to call refrigerator() directly. Instead, it is
recommended to use the try_to_freeze() function (defined in
@@ -95,7 +95,7 @@ after the memory for the image has been freed, we don't want tasks to allocate
additional memory and we prevent them from doing that by freezing them earlier.
[Of course, this also means that device drivers should not allocate substantial
amounts of memory from their .suspend() callbacks before hibernation, but this
-is e separate issue.]
+is a separate issue.]
3. The third reason is to prevent user space processes and some kernel threads
from interfering with the suspending and resuming of devices. A user space
diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt
index bfed898a03f..17e130a8034 100644
--- a/Documentation/power/pm_qos_interface.txt
+++ b/Documentation/power/pm_qos_interface.txt
@@ -4,14 +4,19 @@ This interface provides a kernel and user mode interface for registering
performance expectations by drivers, subsystems and user space applications on
one of the parameters.
-Currently we have {cpu_dma_latency, network_latency, network_throughput} as the
-initial set of pm_qos parameters.
+Two different PM QoS frameworks are available:
+1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput.
+2. the per-device PM QoS framework provides the API to manage the per-device latency
+constraints.
Each parameters have defined units:
* latency: usec
* timeout: usec
* throughput: kbs (kilo bit / sec)
+
+1. PM QoS framework
+
The infrastructure exposes multiple misc device nodes one per implemented
parameter. The set of parameters implement is defined by pm_qos_power_init()
and pm_qos_params.h. This is done because having the available parameters
@@ -23,14 +28,18 @@ an aggregated target value. The aggregated target value is updated with
changes to the request list or elements of the list. Typically the
aggregated target value is simply the max or min of the request values held
in the parameter list elements.
+Note: the aggregated target value is implemented as an atomic variable so that
+reading the aggregated value does not require any locking mechanism.
+
From kernel mode the use of this interface is simple:
-handle = pm_qos_add_request(param_class, target_value):
-Will insert an element into the list for that identified PM_QOS class with the
+void pm_qos_add_request(handle, param_class, target_value):
+Will insert an element into the list for that identified PM QoS class with the
target value. Upon change to this list the new target is recomputed and any
registered notifiers are called only if the target value is now different.
-Clients of pm_qos need to save the returned handle.
+Clients of pm_qos need to save the returned handle for future use in other
+pm_qos API functions.
void pm_qos_update_request(handle, new_target_value):
Will update the list element pointed to by the handle with the new target value
@@ -42,6 +51,20 @@ Will remove the element. After removal it will update the aggregate target and
call the notification tree if the target was changed as a result of removing
the request.
+int pm_qos_request(param_class):
+Returns the aggregated value for a given PM QoS class.
+
+int pm_qos_request_active(handle):
+Returns if the request is still active, i.e. it has not been removed from a
+PM QoS class constraints list.
+
+int pm_qos_add_notifier(param_class, notifier):
+Adds a notification callback function to the PM QoS class. The callback is
+called when the aggregated value for the PM QoS class is changed.
+
+int pm_qos_remove_notifier(int param_class, notifier):
+Removes the notification callback function for the PM QoS class.
+
From user mode:
Only processes can register a pm_qos request. To provide for automatic
@@ -63,4 +86,63 @@ To remove the user mode request for a target value simply close the device
node.
+2. PM QoS per-device latency framework
+
+For each device a list of performance requests is maintained along with
+an aggregated target value. The aggregated target value is updated with
+changes to the request list or elements of the list. Typically the
+aggregated target value is simply the max or min of the request values held
+in the parameter list elements.
+Note: the aggregated target value is implemented as an atomic variable so that
+reading the aggregated value does not require any locking mechanism.
+
+
+From kernel mode the use of this interface is the following:
+
+int dev_pm_qos_add_request(device, handle, value):
+Will insert an element into the list for that identified device with the
+target value. Upon change to this list the new target is recomputed and any
+registered notifiers are called only if the target value is now different.
+Clients of dev_pm_qos need to save the handle for future use in other
+dev_pm_qos API functions.
+
+int dev_pm_qos_update_request(handle, new_value):
+Will update the list element pointed to by the handle with the new target value
+and recompute the new aggregated target, calling the notification trees if the
+target is changed.
+
+int dev_pm_qos_remove_request(handle):
+Will remove the element. After removal it will update the aggregate target and
+call the notification trees if the target was changed as a result of removing
+the request.
+
+s32 dev_pm_qos_read_value(device):
+Returns the aggregated value for a given device's constraints list.
+
+
+Notification mechanisms:
+The per-device PM QoS framework has 2 different and distinct notification trees:
+a per-device notification tree and a global notification tree.
+
+int dev_pm_qos_add_notifier(device, notifier):
+Adds a notification callback function for the device.
+The callback is called when the aggregated value of the device constraints list
+is changed.
+
+int dev_pm_qos_remove_notifier(device, notifier):
+Removes the notification callback function for the device.
+
+int dev_pm_qos_add_global_notifier(notifier):
+Adds a notification callback function in the global notification tree of the
+framework.
+The callback is called when the aggregated value for any device is changed.
+
+int dev_pm_qos_remove_global_notifier(notifier):
+Removes the notification callback function from the global notification tree
+of the framework.
+
+
+From user mode:
+No API for user space access to the per-device latency constraints is provided
+yet - still under discussion.
diff --git a/Documentation/power/regulator/machine.txt b/Documentation/power/regulator/machine.txt
index b42419b52e4..ce63af0a8e3 100644
--- a/Documentation/power/regulator/machine.txt
+++ b/Documentation/power/regulator/machine.txt
@@ -16,7 +16,7 @@ initialisation code by creating a struct regulator_consumer_supply for
each regulator.
struct regulator_consumer_supply {
- struct device *dev; /* consumer */
+ const char *dev_name; /* consumer dev_name() */
const char *supply; /* consumer supply - e.g. "vcc" */
};
@@ -24,13 +24,13 @@ e.g. for the machine above
static struct regulator_consumer_supply regulator1_consumers[] = {
{
- .dev = &platform_consumerB_device.dev,
- .supply = "Vcc",
+ .dev_name = "dev_name(consumer B)",
+ .supply = "Vcc",
},};
static struct regulator_consumer_supply regulator2_consumers[] = {
{
- .dev = &platform_consumerA_device.dev,
+ .dev = "dev_name(consumer A"),
.supply = "Vcc",
},};
@@ -43,6 +43,7 @@ to their supply regulator :-
static struct regulator_init_data regulator1_data = {
.constraints = {
+ .name = "Regulator-1",
.min_uV = 3300000,
.max_uV = 3300000,
.valid_modes_mask = REGULATOR_MODE_NORMAL,
@@ -51,13 +52,19 @@ static struct regulator_init_data regulator1_data = {
.consumer_supplies = regulator1_consumers,
};
+The name field should be set to something that is usefully descriptive
+for the board for configuration of supplies for other regulators and
+for use in logging and other diagnostic output. Normally the name
+used for the supply rail in the schematic is a good choice. If no
+name is provided then the subsystem will choose one.
+
Regulator-1 supplies power to Regulator-2. This relationship must be registered
with the core so that Regulator-1 is also enabled when Consumer A enables its
supply (Regulator-2). The supply regulator is set by the supply_regulator
-field below:-
+field below and co:-
static struct regulator_init_data regulator2_data = {
- .supply_regulator = "regulator_name",
+ .supply_regulator = "Regulator-1",
.constraints = {
.min_uV = 1800000,
.max_uV = 2000000,
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index 6066e3a6b9a..5336149f831 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -43,13 +43,18 @@ struct dev_pm_ops {
...
};
-The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks are
-executed by the PM core for either the device type, or the class (if the device
-type's struct dev_pm_ops object does not exist), or the bus type (if the
-device type's and class' struct dev_pm_ops objects do not exist) of the given
-device (this allows device types to override callbacks provided by bus types or
-classes if necessary). The bus type, device type and class callbacks are
-referred to as subsystem-level callbacks in what follows.
+The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
+are executed by the PM core for either the power domain, or the device type
+(if the device power domain's struct dev_pm_ops does not exist), or the class
+(if the device power domain's and type's struct dev_pm_ops object does not
+exist), or the bus type (if the device power domain's, type's and class'
+struct dev_pm_ops objects do not exist) of the given device, so the priority
+order of callbacks from high to low is that power domain callbacks, device
+type callbacks, class callbacks and bus type callbacks, and the high priority
+one will take precedence over low priority one. The bus type, device type and
+class callbacks are referred to as subsystem-level callbacks in what follows,
+and generally speaking, the power domain callbacks are used for representing
+power domains within a SoC.
By default, the callbacks are always invoked in process context with interrupts
enabled. However, subsystems can use the pm_runtime_irq_safe() helper function
@@ -477,12 +482,14 @@ pm_runtime_autosuspend_expiration()
If pm_runtime_irq_safe() has been called for a device then the following helper
functions may also be used in interrupt context:
+pm_runtime_idle()
pm_runtime_suspend()
pm_runtime_autosuspend()
pm_runtime_resume()
pm_runtime_get_sync()
pm_runtime_put_sync()
pm_runtime_put_sync_suspend()
+pm_runtime_put_sync_autosuspend()
5. Runtime PM Initialization, Device Probing and Removal
@@ -782,6 +789,16 @@ will behave normally, not taking the autosuspend delay into account.
Similarly, if the power.use_autosuspend field isn't set then the autosuspend
helper functions will behave just like the non-autosuspend counterparts.
+Under some circumstances a driver or subsystem may want to prevent a device
+from autosuspending immediately, even though the usage counter is zero and the
+autosuspend delay time has expired. If the ->runtime_suspend() callback
+returns -EAGAIN or -EBUSY, and if the next autosuspend delay expiration time is
+in the future (as it normally would be if the callback invoked
+pm_runtime_mark_last_busy()), the PM core will automatically reschedule the
+autosuspend. The ->runtime_suspend() callback can't do this rescheduling
+itself because no suspend requests of any kind are accepted while the device is
+suspending (i.e., while the callback is running).
+
The implementation is well suited for asynchronous use in interrupt contexts.
However such use inevitably involves races, because the PM core can't
synchronize ->runtime_suspend() callbacks with the arrival of I/O requests.
diff --git a/Documentation/power/suspend-and-cpuhotplug.txt b/Documentation/power/suspend-and-cpuhotplug.txt
new file mode 100644
index 00000000000..f28f9a6f034
--- /dev/null
+++ b/Documentation/power/suspend-and-cpuhotplug.txt
@@ -0,0 +1,275 @@
+Interaction of Suspend code (S3) with the CPU hotplug infrastructure
+
+ (C) 2011 Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
+
+
+I. How does the regular CPU hotplug code differ from how the Suspend-to-RAM
+ infrastructure uses it internally? And where do they share common code?
+
+Well, a picture is worth a thousand words... So ASCII art follows :-)
+
+[This depicts the current design in the kernel, and focusses only on the
+interactions involving the freezer and CPU hotplug and also tries to explain
+the locking involved. It outlines the notifications involved as well.
+But please note that here, only the call paths are illustrated, with the aim
+of describing where they take different paths and where they share code.
+What happens when regular CPU hotplug and Suspend-to-RAM race with each other
+is not depicted here.]
+
+On a high level, the suspend-resume cycle goes like this:
+
+|Freeze| -> |Disable nonboot| -> |Do suspend| -> |Enable nonboot| -> |Thaw |
+|tasks | | cpus | | | | cpus | |tasks|
+
+
+More details follow:
+
+ Suspend call path
+ -----------------
+
+ Write 'mem' to
+ /sys/power/state
+ syfs file
+ |
+ v
+ Acquire pm_mutex lock
+ |
+ v
+ Send PM_SUSPEND_PREPARE
+ notifications
+ |
+ v
+ Freeze tasks
+ |
+ |
+ v
+ disable_nonboot_cpus()
+ /* start */
+ |
+ v
+ Acquire cpu_add_remove_lock
+ |
+ v
+ Iterate over CURRENTLY
+ online CPUs
+ |
+ |
+ | ----------
+ v | L
+ ======> _cpu_down() |
+ | [This takes cpuhotplug.lock |
+ Common | before taking down the CPU |
+ code | and releases it when done] | O
+ | While it is at it, notifications |
+ | are sent when notable events occur, |
+ ======> by running all registered callbacks. |
+ | | O
+ | |
+ | |
+ v |
+ Note down these cpus in | P
+ frozen_cpus mask ----------
+ |
+ v
+ Disable regular cpu hotplug
+ by setting cpu_hotplug_disabled=1
+ |
+ v
+ Release cpu_add_remove_lock
+ |
+ v
+ /* disable_nonboot_cpus() complete */
+ |
+ v
+ Do suspend
+
+
+
+Resuming back is likewise, with the counterparts being (in the order of
+execution during resume):
+* enable_nonboot_cpus() which involves:
+ | Acquire cpu_add_remove_lock
+ | Reset cpu_hotplug_disabled to 0, thereby enabling regular cpu hotplug
+ | Call _cpu_up() [for all those cpus in the frozen_cpus mask, in a loop]
+ | Release cpu_add_remove_lock
+ v
+
+* thaw tasks
+* send PM_POST_SUSPEND notifications
+* Release pm_mutex lock.
+
+
+It is to be noted here that the pm_mutex lock is acquired at the very
+beginning, when we are just starting out to suspend, and then released only
+after the entire cycle is complete (i.e., suspend + resume).
+
+
+
+ Regular CPU hotplug call path
+ -----------------------------
+
+ Write 0 (or 1) to
+ /sys/devices/system/cpu/cpu*/online
+ sysfs file
+ |
+ |
+ v
+ cpu_down()
+ |
+ v
+ Acquire cpu_add_remove_lock
+ |
+ v
+ If cpu_hotplug_disabled is 1
+ return gracefully
+ |
+ |
+ v
+ ======> _cpu_down()
+ | [This takes cpuhotplug.lock
+ Common | before taking down the CPU
+ code | and releases it when done]
+ | While it is at it, notifications
+ | are sent when notable events occur,
+ ======> by running all registered callbacks.
+ |
+ |
+ v
+ Release cpu_add_remove_lock
+ [That's it!, for
+ regular CPU hotplug]
+
+
+
+So, as can be seen from the two diagrams (the parts marked as "Common code"),
+regular CPU hotplug and the suspend code path converge at the _cpu_down() and
+_cpu_up() functions. They differ in the arguments passed to these functions,
+in that during regular CPU hotplug, 0 is passed for the 'tasks_frozen'
+argument. But during suspend, since the tasks are already frozen by the time
+the non-boot CPUs are offlined or onlined, the _cpu_*() functions are called
+with the 'tasks_frozen' argument set to 1.
+[See below for some known issues regarding this.]
+
+
+Important files and functions/entry points:
+------------------------------------------
+
+kernel/power/process.c : freeze_processes(), thaw_processes()
+kernel/power/suspend.c : suspend_prepare(), suspend_enter(), suspend_finish()
+kernel/cpu.c: cpu_[up|down](), _cpu_[up|down](), [disable|enable]_nonboot_cpus()
+
+
+
+II. What are the issues involved in CPU hotplug?
+ -------------------------------------------
+
+There are some interesting situations involving CPU hotplug and microcode
+update on the CPUs, as discussed below:
+
+[Please bear in mind that the kernel requests the microcode images from
+userspace, using the request_firmware() function defined in
+drivers/base/firmware_class.c]
+
+
+a. When all the CPUs are identical:
+
+ This is the most common situation and it is quite straightforward: we want
+ to apply the same microcode revision to each of the CPUs.
+ To give an example of x86, the collect_cpu_info() function defined in
+ arch/x86/kernel/microcode_core.c helps in discovering the type of the CPU
+ and thereby in applying the correct microcode revision to it.
+ But note that the kernel does not maintain a common microcode image for the
+ all CPUs, in order to handle case 'b' described below.
+
+
+b. When some of the CPUs are different than the rest:
+
+ In this case since we probably need to apply different microcode revisions
+ to different CPUs, the kernel maintains a copy of the correct microcode
+ image for each CPU (after appropriate CPU type/model discovery using
+ functions such as collect_cpu_info()).
+
+
+c. When a CPU is physically hot-unplugged and a new (and possibly different
+ type of) CPU is hot-plugged into the system:
+
+ In the current design of the kernel, whenever a CPU is taken offline during
+ a regular CPU hotplug operation, upon receiving the CPU_DEAD notification
+ (which is sent by the CPU hotplug code), the microcode update driver's
+ callback for that event reacts by freeing the kernel's copy of the
+ microcode image for that CPU.
+
+ Hence, when a new CPU is brought online, since the kernel finds that it
+ doesn't have the microcode image, it does the CPU type/model discovery
+ afresh and then requests the userspace for the appropriate microcode image
+ for that CPU, which is subsequently applied.
+
+ For example, in x86, the mc_cpu_callback() function (which is the microcode
+ update driver's callback registered for CPU hotplug events) calls
+ microcode_update_cpu() which would call microcode_init_cpu() in this case,
+ instead of microcode_resume_cpu() when it finds that the kernel doesn't
+ have a valid microcode image. This ensures that the CPU type/model
+ discovery is performed and the right microcode is applied to the CPU after
+ getting it from userspace.
+
+
+d. Handling microcode update during suspend/hibernate:
+
+ Strictly speaking, during a CPU hotplug operation which does not involve
+ physically removing or inserting CPUs, the CPUs are not actually powered
+ off during a CPU offline. They are just put to the lowest C-states possible.
+ Hence, in such a case, it is not really necessary to re-apply microcode
+ when the CPUs are brought back online, since they wouldn't have lost the
+ image during the CPU offline operation.
+
+ This is the usual scenario encountered during a resume after a suspend.
+ However, in the case of hibernation, since all the CPUs are completely
+ powered off, during restore it becomes necessary to apply the microcode
+ images to all the CPUs.
+
+ [Note that we don't expect someone to physically pull out nodes and insert
+ nodes with a different type of CPUs in-between a suspend-resume or a
+ hibernate/restore cycle.]
+
+ In the current design of the kernel however, during a CPU offline operation
+ as part of the suspend/hibernate cycle (the CPU_DEAD_FROZEN notification),
+ the existing copy of microcode image in the kernel is not freed up.
+ And during the CPU online operations (during resume/restore), since the
+ kernel finds that it already has copies of the microcode images for all the
+ CPUs, it just applies them to the CPUs, avoiding any re-discovery of CPU
+ type/model and the need for validating whether the microcode revisions are
+ right for the CPUs or not (due to the above assumption that physical CPU
+ hotplug will not be done in-between suspend/resume or hibernate/restore
+ cycles).
+
+
+III. Are there any known problems when regular CPU hotplug and suspend race
+ with each other?
+
+Yes, they are listed below:
+
+1. When invoking regular CPU hotplug, the 'tasks_frozen' argument passed to
+ the _cpu_down() and _cpu_up() functions is *always* 0.
+ This might not reflect the true current state of the system, since the
+ tasks could have been frozen by an out-of-band event such as a suspend
+ operation in progress. Hence, it will lead to wrong notifications being
+ sent during the cpu online/offline events (eg, CPU_ONLINE notification
+ instead of CPU_ONLINE_FROZEN) which in turn will lead to execution of
+ inappropriate code by the callbacks registered for such CPU hotplug events.
+
+2. If a regular CPU hotplug stress test happens to race with the freezer due
+ to a suspend operation in progress at the same time, then we could hit the
+ situation described below:
+
+ * A regular cpu online operation continues its journey from userspace
+ into the kernel, since the freezing has not yet begun.
+ * Then freezer gets to work and freezes userspace.
+ * If cpu online has not yet completed the microcode update stuff by now,
+ it will now start waiting on the frozen userspace in the
+ TASK_UNINTERRUPTIBLE state, in order to get the microcode image.
+ * Now the freezer continues and tries to freeze the remaining tasks. But
+ due to this wait mentioned above, the freezer won't be able to freeze
+ the cpu online hotplug task and hence freezing of tasks fails.
+
+ As a result of this task freezing failure, the suspend operation gets
+ aborted.
diff --git a/Documentation/power/userland-swsusp.txt b/Documentation/power/userland-swsusp.txt
index 1101bee4e82..0e870825c1b 100644
--- a/Documentation/power/userland-swsusp.txt
+++ b/Documentation/power/userland-swsusp.txt
@@ -77,7 +77,8 @@ SNAPSHOT_SET_SWAP_AREA - set the resume partition and the offset (in <PAGE_SIZE>
resume_swap_area, as defined in kernel/power/suspend_ioctls.h,
containing the resume device specification and the offset); for swap
partitions the offset is always 0, but it is different from zero for
- swap files (see Documentation/swsusp-and-swap-files.txt for details).
+ swap files (see Documentation/power/swsusp-and-swap-files.txt for
+ details).
SNAPSHOT_PLATFORM_SUPPORT - enable/disable the hibernation platform support,
depending on the argument value (enable, if the argument is nonzero)