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

NAME

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

SYNOPSIS

#include <sys/ddi.h>
#include <sys/sunddi.h>


int ddi_dev_is_needed(dev_info_t *dip, int component, int level);

INTERFACE LEVEL

illumos DDI specific (illumos DDI)

PARAMETERS

dip
Pointer to the device's dev_info structure.


component
Component of the driver which is needed.


level
Power level at which the component is needed.

DESCRIPTION

The ddi_dev_is_needed() function is obsolete and will be removed in a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().

RETURN VALUES

The ddi_dev_is_needed() function returns:

DDI_SUCCESS
Power successfully set to the requested level.


DDI_FAILURE
An error occurred.

EXAMPLES

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);

...

}

CONTEXT

This function can be called from user or kernel context.

ATTRIBUTES

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


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Obsolete |
+--------------------+-----------------+

SEE ALSO

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 DDI_DEV_IS_NEEDED(9F)