text: /*
   * drivers/base/power/domain_governor.c - Governors for device PM domains.
   *
   * Copyright (C) 2011 Rafael J. Wysocki <rjw@sisk.pl>, Renesas Electronics Corp.
   *
   * This file is released under the GPLv2.
   */
  
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/pm_domain.h>
  #include <linux/pm_qos.h>
  #include <linux/hrtimer.h>
  
  #ifdef CONFIG_PM_RUNTIME
  
  /**
   * default_stop_ok - Default PM domain governor routine for stopping devices.
   * @dev: Device to check.
   */
  bool default_stop_ok(struct device *dev)
  {
  	struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
  
  	dev_dbg(dev, "%s()\n", __func__);
  
  	if (dev->power.max_time_suspended_ns < 0 || td->break_even_ns == 0)
  		return true;
  
  	return td->stop_latency_ns + td->start_latency_ns < td->break_even_ns
  		&& td->break_even_ns < dev->power.max_time_suspended_ns;
  }
  
  /**
   * default_power_down_ok - Default generic PM domain power off governor routine.
   * @pd: PM domain to check.
   *
   * This routine must be executed under the PM domain's lock.
   */
  static bool default_power_down_ok(struct dev_pm_domain *pd)
  {
  	struct generic_pm_domain *genpd = pd_to_genpd(pd);
  	struct gpd_link *link;
  	struct pm_domain_data *pdd;
  	s64 min_dev_off_time_ns;
  	s64 off_on_time_ns;
  	ktime_t time_now = ktime_get();
  
  	off_on_time_ns = genpd->power_off_latency_ns +
  				genpd->power_on_latency_ns;
  	/*
  	 * It doesn't make sense to remove power from the domain if saving
  	 * the state of all devices in it and the power off/power on operations
  	 * take too much time.
  	 *
  	 * All devices in this domain have been stopped already at this point.
  	 */
  	list_for_each_entry(pdd, &genpd->dev_list, list_node) {
  		if (pdd->dev->driver)
  			off_on_time_ns +=
  				to_gpd_data(pdd)->td.save_state_latency_ns;
  	}
  
  	/*
  	 * Check if subdomains can be off for enough time.
  	 *
  	 * All subdomains have been powered off already at this point.
  	 */
  	list_for_each_entry(link, &genpd->master_links, master_node) {
  		struct generic_pm_domain *sd = link->slave;
  		s64 sd_max_off_ns = sd->max_off_time_ns;
  
  		if (sd_max_off_ns < 0)
  			continue;
  
  		sd_max_off_ns -= ktime_to_ns(ktime_sub(time_now,
  						       sd->power_off_time));
  		/*
  		 * Check if the subdomain is allowed to be off long enough for
  		 * the current domain to turn off and on (that's how much time
  		 * it will have to wait worst case).
  		 */
  		if (sd_max_off_ns <= off_on_time_ns)
  			return false;
  	}
  
  	/*
  	 * Check if the devices in the domain can be off enough time.
  	 */
  	min_dev_off_time_ns = -1;
  	list_for_each_entry(pdd, &genpd->dev_list, list_node) {
  		struct gpd_timing_data *td;
  		struct device *dev = pdd->dev;
  		s64 dev_off_time_ns;
  
  		if (!dev->driver || dev->power.max_time_suspended_ns < 0)
  			continue;
  
  		td = &to_gpd_data(pdd)->td;
  		dev_off_time_ns = dev->power.max_time_suspended_ns -
  			(td->start_latency_ns + td->restore_state_latency_ns +
  				ktime_to_ns(ktime_sub(time_now,
  						dev->power.suspend_time)));
  		if (dev_off_time_ns <= off_on_time_ns)
  			return false;
  
  		if (min_dev_off_time_ns > dev_off_time_ns
  		    || min_dev_off_time_ns < 0)
  			min_dev_off_time_ns = dev_off_time_ns;
  	}
  
  	if (min_dev_off_time_ns < 0) {
  		/*
  		 * There are no latency constraints, so the domain can spend
  		 * arbitrary time in the "off" state.
  		 */
  		genpd->max_off_time_ns = -1;
  		return true;
  	}
  
  	/*
  	 * The difference between the computed minimum delta and the time needed
  	 * to turn the domain on is the maximum theoretical time this domain can
  	 * spend in the "off" state.
  	 */
  	min_dev_off_time_ns -= genpd->power_on_latency_ns;
  
  	/*
  	 * If the difference between the computed minimum delta and the time
  	 * needed to turn the domain off and back on on is smaller than the
  	 * domain's power break even time, removing power from the domain is not
  	 * worth it.
  	 */
  	if (genpd->break_even_ns >
  	    min_dev_off_time_ns - genpd->power_off_latency_ns)
  		return false;
  
  	genpd->max_off_time_ns = min_dev_off_time_ns;
  	return true;
  }
  
  static bool always_on_power_down_ok(struct dev_pm_domain *domain)
  {
  	return false;
  }
  
  #else /* !CONFIG_PM_RUNTIME */
  
  bool default_stop_ok(struct device *dev)
  {
  	return false;
  }
  
  #define default_power_down_ok	NULL
  #define always_on_power_down_ok	NULL
  
  #endif /* !CONFIG_PM_RUNTIME */
  
  struct dev_power_governor simple_qos_governor = {
  	.stop_ok = default_stop_ok,
  	.power_down_ok = default_power_down_ok,
  };
  
  /**
   * pm_genpd_gov_always_on - A governor implementing an always-on policy
   */
  struct dev_power_governor pm_domain_always_on_gov = {
  	.power_down_ok = always_on_power_down_ok,
  	.stop_ok = default_stop_ok,
  };
  