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Merge branch 'power-supply-scope' of git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen

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This commit is contained in:
Anton Vorontsov 2012-01-04 09:09:35 +04:00
commit 251f39fe42
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2
Documentation/power/00-INDEX
View file

@ -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

26
Documentation/power/basic-pm-debugging.txt
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@ -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.

8
Documentation/power/devices.txt
View file

@ -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

8
Documentation/power/freezing-of-tasks.txt
View file

@ -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

92
Documentation/power/pm_qos_interface.txt
View file

@ -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.

19
Documentation/power/regulator/machine.txt
View file

@ -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,

31
Documentation/power/runtime_pm.txt
View file

@ -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.

275
Documentation/power/suspend-and-cpuhotplug.txt Normal file
View file

@ -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.

3
Documentation/power/userland-swsusp.txt
View file

@ -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)