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Writing Device Drivers
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Power Management Device Access Example

If power management is supported, and detach(9E) and attach(9E) are used as in Example 12-6 and Example 12-7, then access to the device can be made from user context, for example, from read(2), write(2), and ioctl(2).

The following example demonstrates this approach. The example assumes that the operation about to be performed requires a component component that is operating at power level level.

Example 12-8 Device Access
mutex_enter(&xsp->mu);
/*
 * Block command while device is suspended by DDI_SUSPEND
 */
while (xsp->xx_suspended)
    cv_wait(&xsp->xx_suspend_cv, &xsp->mu);
/*
 * Mark component busy so xx_power() will reject attempt to lower power
 */
xsp->xx_busy[component]++;
if (pm_busy_component(dip, component) != DDI_SUCCESS) {
    xsp->xx_busy[component]--;
    /*
     * Log error and abort
     */
}
if (xsp->xx_power_level[component] < level) {
    mutex_exit(&xsp->mu);
    if (pm_raise_power(dip, component, level) != DDI_SUCCESS) {
        /*
         * Log error and abort
         */
    }
    mutex_enter(&xsp->mu);
}

The code fragment in the following example can be used when device operation completes, for example, in the device's interrupt handler.

Example 12-9 Device Operation Completion
/*
 * For each command completion, decrement the busy count and unstack
 * the pm_busy_component() call by calling pm_idle_component(). This
 * will allow device power to be lowered when all commands complete
 * (all pm_busy_component() counts are unstacked)
 */
xsp->xx_busy[component]--;
if (pm_idle_component(dip, component) != DDI_SUCCESS) {
    xsp->xx_busy[component]++;
    /*
     * Log error and abort
     */
}
/*
 * If no more outstanding commands, wake up anyone (like DDI_SUSPEND)
 * waiting for all commands to  be completed
 */
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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire