diff options
| -rw-r--r-- | include/linux/pm.h | 229 |
1 files changed, 134 insertions, 95 deletions
diff --git a/include/linux/pm.h b/include/linux/pm.h index 5c4c8b18c8b..3f3ed83a9aa 100644 --- a/include/linux/pm.h +++ b/include/linux/pm.h @@ -54,118 +54,145 @@ typedef struct pm_message { /** * struct dev_pm_ops - device PM callbacks * - * Several driver power state transitions are externally visible, affecting + * Several device power state transitions are externally visible, affecting * the state of pending I/O queues and (for drivers that touch hardware) * interrupts, wakeups, DMA, and other hardware state. There may also be - * internal transitions to various low power modes, which are transparent + * internal transitions to various low-power modes which are transparent * to the rest of the driver stack (such as a driver that's ON gating off * clocks which are not in active use). * - * The externally visible transitions are handled with the help of the following - * callbacks included in this structure: - * - * @prepare: Prepare the device for the upcoming transition, but do NOT change - * its hardware state. Prevent new children of the device from being - * registered after @prepare() returns (the driver's subsystem and - * generally the rest of the kernel is supposed to prevent new calls to the - * probe method from being made too once @prepare() has succeeded). If - * @prepare() detects a situation it cannot handle (e.g. registration of a - * child already in progress), it may return -EAGAIN, so that the PM core - * can execute it once again (e.g. after the new child has been registered) - * to recover from the race condition. This method is executed for all - * kinds of suspend transitions and is followed by one of the suspend - * callbacks: @suspend(), @freeze(), or @poweroff(). - * The PM core executes @prepare() for all devices before starting to - * execute suspend callbacks for any of them, so drivers may assume all of - * the other devices to be present and functional while @prepare() is being - * executed. In particular, it is safe to make GFP_KERNEL memory - * allocations from within @prepare(). However, drivers may NOT assume - * anything about the availability of the user space at that time and it - * is not correct to request firmware from within @prepare() (it's too - * late to do that). [To work around this limitation, drivers may - * register suspend and hibernation notifiers that are executed before the - * freezing of tasks.] + * The externally visible transitions are handled with the help of callbacks + * included in this structure in such a way that two levels of callbacks are + * involved. First, the PM core executes callbacks provided by PM domains, + * device types, classes and bus types. They are the subsystem-level callbacks + * supposed to execute callbacks provided by device drivers, although they may + * choose not to do that. If the driver callbacks are executed, they have to + * collaborate with the subsystem-level callbacks to achieve the goals + * appropriate for the given system transition, given transition phase and the + * subsystem the device belongs to. + * + * @prepare: The principal role of this callback is to prevent new children of + * the device from being registered after it has returned (the driver's + * subsystem and generally the rest of the kernel is supposed to prevent + * new calls to the probe method from being made too once @prepare() has + * succeeded). If @prepare() detects a situation it cannot handle (e.g. + * registration of a child already in progress), it may return -EAGAIN, so + * that the PM core can execute it once again (e.g. after a new child has + * been registered) to recover from the race condition. + * This method is executed for all kinds of suspend transitions and is + * followed by one of the suspend callbacks: @suspend(), @freeze(), or + * @poweroff(). The PM core executes subsystem-level @prepare() for all + * devices before starting to invoke suspend callbacks for any of them, so + * generally devices may be assumed to be functional or to respond to + * runtime resume requests while @prepare() is being executed. However, + * device drivers may NOT assume anything about the availability of user + * space at that time and it is NOT valid to request firmware from within + * @prepare() (it's too late to do that). It also is NOT valid to allocate + * substantial amounts of memory from @prepare() in the GFP_KERNEL mode. + * [To work around these limitations, drivers may register suspend and + * hibernation notifiers to be executed before the freezing of tasks.] * * @complete: Undo the changes made by @prepare(). This method is executed for * all kinds of resume transitions, following one of the resume callbacks: * @resume(), @thaw(), @restore(). Also called if the state transition - * fails before the driver's suspend callback (@suspend(), @freeze(), - * @poweroff()) can be executed (e.g. if the suspend callback fails for one + * fails before the driver's suspend callback: @suspend(), @freeze() or + * @poweroff(), can be executed (e.g. if the suspend callback fails for one * of the other devices that the PM core has unsuccessfully attempted to * suspend earlier). - * The PM core executes @complete() after it has executed the appropriate - * resume callback for all devices. + * The PM core executes subsystem-level @complete() after it has executed + * the appropriate resume callbacks for all devices. * * @suspend: Executed before putting the system into a sleep state in which the - * contents of main memory are preserved. Quiesce the device, put it into - * a low power state appropriate for the upcoming system state (such as - * PCI_D3hot), and enable wakeup events as appropriate. + * contents of main memory are preserved. The exact action to perform + * depends on the device's subsystem (PM domain, device type, class or bus + * type), but generally the device must be quiescent after subsystem-level + * @suspend() has returned, so that it doesn't do any I/O or DMA. + * Subsystem-level @suspend() is executed for all devices after invoking + * subsystem-level @prepare() for all of them. * * @resume: Executed after waking the system up from a sleep state in which the - * contents of main memory were preserved. Put the device into the - * appropriate state, according to the information saved in memory by the - * preceding @suspend(). The driver starts working again, responding to - * hardware events and software requests. The hardware may have gone - * through a power-off reset, or it may have maintained state from the - * previous suspend() which the driver may rely on while resuming. On most - * platforms, there are no restrictions on availability of resources like - * clocks during @resume(). + * contents of main memory were preserved. The exact action to perform + * depends on the device's subsystem, but generally the driver is expected + * to start working again, responding to hardware events and software + * requests (the device itself may be left in a low-power state, waiting + * for a runtime resume to occur). The state of the device at the time its + * driver's @resume() callback is run depends on the platform and subsystem + * the device belongs to. On most platforms, there are no restrictions on + * availability of resources like clocks during @resume(). + * Subsystem-level @resume() is executed for all devices after invoking + * subsystem-level @resume_noirq() for all of them. * * @freeze: Hibernation-specific, executed before creating a hibernation image. - * Quiesce operations so that a consistent image can be created, but do NOT - * otherwise put the device into a low power device state and do NOT emit - * system wakeup events. Save in main memory the device settings to be - * used by @restore() during the subsequent resume from hibernation or by - * the subsequent @thaw(), if the creation of the image or the restoration - * of main memory contents from it fails. + * Analogous to @suspend(), but it should not enable the device to signal + * wakeup events or change its power state. The majority of subsystems + * (with the notable exception of the PCI bus type) expect the driver-level + * @freeze() to save the device settings in memory to be used by @restore() + * during the subsequent resume from hibernation. + * Subsystem-level @freeze() is executed for all devices after invoking + * subsystem-level @prepare() for all of them. * * @thaw: Hibernation-specific, executed after creating a hibernation image OR - * if the creation of the image fails. Also executed after a failing + * if the creation of an image has failed. Also executed after a failing * attempt to restore the contents of main memory from such an image. * Undo the changes made by the preceding @freeze(), so the device can be * operated in the same way as immediately before the call to @freeze(). + * Subsystem-level @thaw() is executed for all devices after invoking + * subsystem-level @thaw_noirq() for all of them. It also may be executed + * directly after @freeze() in case of a transition error. * * @poweroff: Hibernation-specific, executed after saving a hibernation image. - * Quiesce the device, put it into a low power state appropriate for the - * upcoming system state (such as PCI_D3hot), and enable wakeup events as - * appropriate. + * Analogous to @suspend(), but it need not save the device's settings in + * memory. + * Subsystem-level @poweroff() is executed for all devices after invoking + * subsystem-level @prepare() for all of them. * * @restore: Hibernation-specific, executed after restoring the contents of main - * memory from a hibernation image. Driver starts working again, - * responding to hardware events and software requests. Drivers may NOT - * make ANY assumptions about the hardware state right prior to @restore(). - * On most platforms, there are no restrictions on availability of - * resources like clocks during @restore(). - * - * @suspend_noirq: Complete the operations of ->suspend() by carrying out any - * actions required for suspending the device that need interrupts to be - * disabled - * - * @resume_noirq: Prepare for the execution of ->resume() by carrying out any - * actions required for resuming the device that need interrupts to be - * disabled - * - * @freeze_noirq: Complete the operations of ->freeze() by carrying out any - * actions required for freezing the device that need interrupts to be - * disabled - * - * @thaw_noirq: Prepare for the execution of ->thaw() by carrying out any - * actions required for thawing the device that need interrupts to be - * disabled - * - * @poweroff_noirq: Complete the operations of ->poweroff() by carrying out any - * actions required for handling the device that need interrupts to be - * disabled - * - * @restore_noirq: Prepare for the execution of ->restore() by carrying out any - * actions required for restoring the operations of the device that need - * interrupts to be disabled + * memory from a hibernation image, analogous to @resume(). + * + * @suspend_noirq: Complete the actions started by @suspend(). Carry out any + * additional operations required for suspending the device that might be + * racing with its driver's interrupt handler, which is guaranteed not to + * run while @suspend_noirq() is being executed. + * It generally is expected that the device will be in a low-power state + * (appropriate for the target system sleep state) after subsystem-level + * @suspend_noirq() has returned successfully. If the device can generate + * system wakeup signals and is enabled to wake up the system, it should be + * configured to do so at that time. However, depending on the platform + * and device's subsystem, @suspend() may be allowed to put the device into + * the low-power state and configure it to generate wakeup signals, in + * which case it generally is not necessary to define @suspend_noirq(). + * + * @resume_noirq: Prepare for the execution of @resume() by carrying out any + * operations required for resuming the device that might be racing with + * its driver's interrupt handler, which is guaranteed not to run while + * @resume_noirq() is being executed. + * + * @freeze_noirq: Complete the actions started by @freeze(). Carry out any + * additional operations required for freezing the device that might be + * racing with its driver's interrupt handler, which is guaranteed not to + * run while @freeze_noirq() is being executed. + * The power state of the device should not be changed by either @freeze() + * or @freeze_noirq() and it should not be configured to signal system + * wakeup by any of these callbacks. + * + * @thaw_noirq: Prepare for the execution of @thaw() by carrying out any + * operations required for thawing the device that might be racing with its + * driver's interrupt handler, which is guaranteed not to run while + * @thaw_noirq() is being executed. + * + * @poweroff_noirq: Complete the actions started by @poweroff(). Analogous to + * @suspend_noirq(), but it need not save the device's settings in memory. + * + * @restore_noirq: Prepare for the execution of @restore() by carrying out any + * operations required for thawing the device that might be racing with its + * driver's interrupt handler, which is guaranteed not to run while + * @restore_noirq() is being executed. Analogous to @resume_noirq(). * * All of the above callbacks, except for @complete(), return error codes. * However, the error codes returned by the resume operations, @resume(), - * @thaw(), @restore(), @resume_noirq(), @thaw_noirq(), and @restore_noirq() do + * @thaw(), @restore(), @resume_noirq(), @thaw_noirq(), and @restore_noirq(), do * not cause the PM core to abort the resume transition during which they are - * returned. The error codes returned in that cases are only printed by the PM + * returned. The error codes returned in those cases are only printed by the PM * core to the system logs for debugging purposes. Still, it is recommended * that drivers only return error codes from their resume methods in case of an * unrecoverable failure (i.e. when the device being handled refuses to resume @@ -174,31 +201,43 @@ typedef struct pm_message { * their children. * * It is allowed to unregister devices while the above callbacks are being - * executed. However, it is not allowed to unregister a device from within any - * of its own callbacks. + * executed. However, a callback routine must NOT try to unregister the device + * it was called for, although it may unregister children of that device (for + * example, if it detects that a child was unplugged while the system was + * asleep). + * + * Refer to Documentation/power/devices.txt for more information about the role + * of the above callbacks in the system suspend process. * - * There also are the following callbacks related to run-time power management - * of devices: + * There also are callbacks related to runtime power management of devices. + * Again, these callbacks are executed by the PM core only for subsystems + * (PM domains, device types, classes and bus types) and the subsystem-level + * callbacks are supposed to invoke the driver callbacks. Moreover, the exact + * actions to be performed by a device driver's callbacks generally depend on + * the platform and subsystem the device belongs to. * * @runtime_suspend: Prepare the device for a condition in which it won't be * able to communicate with the CPU(s) and RAM due to power management. - * This need not mean that the device should be put into a low power state. + * This need not mean that the device should be put into a low-power state. * For example, if the device is behind a link which is about to be turned * off, the device may remain at full power. If the device does go to low - * power and is capable of generating run-time wake-up events, remote - * wake-up (i.e., a hardware mechanism allowing the device to request a - * change of its power state via a wake-up event, such as PCI PME) should - * be enabled for it. + * power and is capable of generating runtime wakeup events, remote wakeup + * (i.e., a hardware mechanism allowing the device to request a change of + * its power state via an interrupt) should be enabled for it. * * @runtime_resume: Put the device into the fully active state in response to a - * wake-up event generated by hardware or at the request of software. If - * necessary, put the device into the full power state and restore its + * wakeup event generated by hardware or at the request of software. If + * necessary, put the device into the full-power state and restore its * registers, so that it is fully operational. * - * @runtime_idle: Device appears to be inactive and it might be put into a low - * power state if all of the necessary conditions are satisfied. Check + * @runtime_idle: Device appears to be inactive and it might be put into a + * low-power state if all of the necessary conditions are satisfied. Check * these conditions and handle the device as appropriate, possibly queueing * a suspend request for it. The return value is ignored by the PM core. + * + * Refer to Documentation/power/runtime_pm.txt for more information about the + * role of the above callbacks in device runtime power management. + * */ struct dev_pm_ops { |