Manual Pages for UNIX Operating System command usage for man ddi_dev_is_needed

Kernel Functions for Drivers                ddi_dev_is_needed(9F)



NAME
     ddi_dev_is_needed - inform the system that a  device's  com-
     ponent is required

SYNOPSIS
     #include 
     #include 



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


INTERFACE LEVEL
     Solaris DDI specific (Solaris 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     The ddi_dev_is_needed() function is  obsolete  and  will  be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  phy-
     sical  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().



SunOS 5.11           Last change: 7 Dec 2003                    1






Kernel Functions for Drivers                ddi_dev_is_needed(9F)



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);

       ...

       }





SunOS 5.11           Last change: 7 Dec 2003                    2






Kernel Functions for Drivers                ddi_dev_is_needed(9F)



CONTEXT
     This function can be called from user or kernel context.

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Obsolete                    |
    |_____________________________|_____________________________|


SEE ALSO
     pm(7D),    pm-components(9P),    attach(9E),     detach(9E),
     power(9E), pm_busy_component(9F), pm_idle_component(9F)


     Writing Device Drivers

































SunOS 5.11           Last change: 7 Dec 2003                    3