DDI_DEV_IS_NEEDED(9F) Kernel Functions for Drivers DDI_DEV_IS_NEEDED(9F)

ddi_dev_is_needed - inform the system that a device's component is required

#include <sys/ddi.h>
#include <sys/sunddi.h>
int ddi_dev_is_needed(dev_info_t *dip, int component, int level);

illumos DDI specific (illumos DDI)


Pointer to the device's dev_info structure.


Component of the driver which is needed.


Power level at which the component is needed.

The ddi_dev_is_needed() function is obsolete and will be removed in a future release. It is recommended that device drivers use pm_raise_power(9F) and pm_lower_power(9F).

The ddi_dev_is_needed() function informs the system that a device component is needed at the specified power level. The level argument must be non-zero.

This function sets a component to the required level and sets all devices which depend on this to their normal power levels.

The state of the device should be examined before each physical access. The ddi_dev_is_needed() function should be called to set a component to the required power level if the operation to be performed requires the component to be at a power level other than its current level.

The ddi_dev_is_needed() function might cause re-entry of the driver. Deadlock may result if driver locks are held across the call to ddi_dev_is_needed().

The ddi_dev_is_needed() function returns:


Power successfully set to the requested level.


An error occurred.

Example 1 disk driver code

A hypothetical disk driver might include this code:

static int xxdisk_spun_down(struct xxstate *xsp) { return (xsp->power_level[DISK_COMPONENT] < POWER_SPUN_UP); } static int xxdisk_strategy(struct buf *bp) { ... mutex_enter(&xxstate_lock); /* * Since we have to drop the mutex, we have to do this in a loop * in case we get preempted and the device gets taken away from * us again */ while (device_spun_down(sp)) { mutex_exit(&xxstate_lock); if (ddi_dev_is_needed(xsp->mydip, XXDISK_COMPONENT, XXPOWER_SPUN_UP) != DDI_SUCCESS) { bioerror(bp,EIO); biodone(bp); return (0); } mutex_enter(&xxstate_lock); } xsp->device_busy++; mutex_exit(&xxstate_lock); ... }

This function can be called from user or kernel context.

See attributes(7) for descriptions of the following attributes:

Interface Stability Obsolete

pm(4D), attach(9E), detach(9E), power(9E), pm_busy_component(9F), pm_idle_component(9F), pm-components(9P)

Writing Device Drivers

December 7, 2003 OmniOS