Power management commands for the seL4 Driver API


/* Driver power states supported by the API.
 * These are used by both seL4drv_mgmt_power()
 * and seL4drv_mgmt_power_features().
#define SEL4DRV_MGMT_POWER_BOOT       (1<<0)
#define SEL4DRV_MGMT_POWER_WAKEUP     (1<<1)
#define SEL4DRV_MGMT_POWER_SLEEP      (1<<2)
#define SEL4DRV_MGMT_POWER_KILL       (1<<5)


void seL4drv_mgmt_critical_event_subscription_ind();
void seL4drv_mgmt_power();
void seL4drv_mgmt_power_features(uint32_t *features_bitmap);
void seL4drv_mgmt_enumerate_children();

Power state specifications

  • SEL4DRV_MGMT_POWER_BOOT: Support for this power management command is required of all drivers. This is actually the global entry point for a driver, and it will be called only once during a particular device instance’s lifetime. After the driver returns from this function call, the environment will assume that the device has been initialized and is ready to accept requests.
  • SEL4DRV_MGMT_POWER_WAKEUP: Support for this power management command is required of all drivers which support the SLEEP or DEEP_SLEEP commands. Instructs the driver to resume operation after a SLEEP or DEEP_SLEEP command. The driver is expected to do any necessary re-initialization of the hardware to get the driver back into an operational state. If there were asynchronous requests outstanding before the device was put into a low-power mode, the driver should re-trigger and resume the normal processing of such requests.
  • SEL4DRV_MGMT_POWER_SLEEP: Indicates to the driver that the device is about to be placed into a light sleep state. In such a state, the caches of its underlying and dependent hardware are guaranteed not to be flushed, and there will be no need to reinitialize the buses after wakeup. If the device does not support such a light sleep mode, the device shall return an error code.
  • SEL4DRV_MGMT_POWER_DEEP_SLEEP: Indicates to the driver that the environment would like to place the device into a sleep state in which there is no guarantee that hardware caches and buffers will be preserved. Furthermore, there is no guarantee that bus configuration will hold across this transition. The driver shall cleanly commit the effect of all current operations, and place any unsatisfied asynchronous requests on hold, before putting the device into a state that is compatible with this sleep state.
  • SEL4DRV_MGMT_POWER_SHUTDOWN: Support for this power management command is required of all drivers. Indicates that the device should be placed into a state in which it would be safe to cut off power to the device. Such a state should at least guarantee that all clients’ data is quickly cleaned out to permanent storage, and that all effects requested by clients are committed. If it is possible to satisfy any outstanding asynchronous requests the driver should commit to completing them, but it should reject all future requests from that point onward.
  • SEL4DRV_MGMT_POWER_KILL: Support for this power management command is required of all drivers. Indicates that the environment wants to kill the device, NOW. Any outstanding asynchronous requests should be canceled and the driver should then place itself into a state that is compatible with the SEL4DRV_MGMT_POWER_SHUTDOWN command.


seL4drv_mgmt_critical_event_subscription_ind(): Async

This function enables the environment to call into the driver, and give it an asynchronous context block which it should hold on to. If at any point the driver encounters a situation which requires it to ask the environment to shut it down, it can asynchronously callback into the environment to make such a request.

The reason for this function is to enable the driver to report to the environment when it has found itself in an invalid operational state which it cannot recover from. This is not a necessary function to implement, and it is likely to be a blank function for most implementations.

seL4drv_mgmt_power(): Async

This operation is called by the environment to place the device instance into one of the power states outlined above. It is important to note that SEL4DRV_MGMT_POWER_BOOT is actually just a global entry point into the driver.

When it comes to placing devices into low power states, the environment must understand that it is not the responsibility of the driver to communicate the power management request to its children. If the environment would like to place an entire hardware bus in a low-power mode, then the environment must walk its own internal device tree, and for each descendant of the target bus, it must manually ask that descendent to enter a power state that is compatible with the power state it wishes to place the bus into. That is, parent devices are not responsible for recursing downward and calling their children to instruct them to enter power states on behalf of the environment.

The same applies for waking devices up from power states. If the environment wishes to wake a particular child device, it must manually ensure that all of that device’s parents are in a suitable power state to enable operation.

seL4drv_mgmt_power_features(): Sync

This function returns a bitmap of the supported driver power states (See #constants). All drivers are required to support at minimum, the following states:


If any of these is not supported by the driver, the environment is free to respond in an implementation specific manner, including refusing to load the driver.

The driver is only required to support the SEL4DRV_MGMT_POWER_WAKEUP command if either the SEL4DRV_MGMT_POWER_SLEEP or SEL4DRV_MGMT_POWER_DEEP_SLEEP command is supported. If either the SLEEP or DEEP_SLEEP command is supported and there is no support for the SEL4DRV_MGMT_POWER_WAKEUP command, the environment should assume that the SLEEP or DEEP_SLEEP operations are not adequately supported.

Child enumeration

See the main article: