1ddi_dev_is_needed(9F) Kernel Functions for Drivers ddi_dev_is_needed(9F)
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6 ddi_dev_is_needed - inform the system that a device's component is
7 required
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10 #include <sys/ddi.h>
11 #include <sys/sunddi.h>
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15 int ddi_dev_is_needed(dev_info_t *dip, int component, int level);
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19 Solaris DDI specific (Solaris DDI)
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22 dip Pointer to the device's dev_info structure.
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25 component Component of the driver which is needed.
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28 level Power level at which the component is needed.
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32 The ddi_dev_is_needed() function is obsolete and will be removed in a
33 future release. It is recommended that device drivers use
34 pm_raise_power(9F) and pm_lower_power(9F).
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37 The ddi_dev_is_needed() function informs the system that a device com‐
38 ponent is needed at the specified power level. The level argument must
39 be non-zero.
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42 This function sets a component to the required level and sets all
43 devices which depend on this to their normal power levels.
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46 The state of the device should be examined before each physical access.
47 The ddi_dev_is_needed() function should be called to set a component to
48 the required power level if the operation to be performed requires the
49 component to be at a power level other than its current level.
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52 The ddi_dev_is_needed() function might cause re-entry of the driver.
53 Deadlock may result if driver locks are held across the call to
54 ddi_dev_is_needed().
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57 The ddi_dev_is_needed() function returns:
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59 DDI_SUCCESS Power successfully set to the requested level.
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62 DDI_FAILURE An error occurred.
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66 Example 1 disk driver code
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69 A hypothetical disk driver might include this code:
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72 static int
73 xxdisk_spun_down(struct xxstate *xsp)
74 {
75 return (xsp->power_level[DISK_COMPONENT] < POWER_SPUN_UP);
76 }
77 static int
78 xxdisk_strategy(struct buf *bp)
79 {
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81 ...
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83 mutex_enter(&xxstate_lock);
84 /*
85 * Since we have to drop the mutex, we have to do this in a loop
86 * in case we get preempted and the device gets taken away from
87 * us again
88 */
89 while (device_spun_down(sp)) {
90 mutex_exit(&xxstate_lock);
91 if (ddi_dev_is_needed(xsp->mydip,
92 XXDISK_COMPONENT, XXPOWER_SPUN_UP) != DDI_SUCCESS) {
93 bioerror(bp,EIO);
94 biodone(bp);
95 return (0);
96 }
97 mutex_enter(&xxstate_lock);
98 }
99 xsp->device_busy++;
100 mutex_exit(&xxstate_lock);
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102 ...
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104 }
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108 This function can be called from user or kernel context.
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111 See attributes(5) for descriptions of the following attributes:
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116 ┌─────────────────────────────┬─────────────────────────────┐
117 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
118 ├─────────────────────────────┼─────────────────────────────┤
119 │Interface Stability │Obsolete │
120 └─────────────────────────────┴─────────────────────────────┘
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123 pm(7D), pm-components(9P), attach(9E), detach(9E), power(9E),
124 pm_busy_component(9F), pm_idle_component(9F)
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127 Writing Device Drivers
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131SunOS 5.11 7 Dec 2003 ddi_dev_is_needed(9F)