domain_governor.c

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/*
 * drivers/base/power/domain_governor.c - Governors for device PM domains.
 *
 * Copyright (C) 2011 Rafael J. Wysocki <[email protected]>, 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

static int dev_update_qos_constraint(struct device *dev, void *data)
{
    s64 *constraint_ns_p = data;
    s32 constraint_ns = -1;

    if (dev->power.subsys_data && dev->power.subsys_data->domain_data)
        constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;

    if (constraint_ns < 0) {
        constraint_ns = dev_pm_qos_read_value(dev);
        constraint_ns *= NSEC_PER_USEC;
    }
    if (constraint_ns == 0)
        return 0;

    /*
     * constraint_ns cannot be negative here, because the device has been
     * suspended.
     */
    if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
        *constraint_ns_p = constraint_ns;

    return 0;
}

bool default_stop_ok(struct device *dev)
{
    struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
    unsigned long flags;
    s64 constraint_ns;

    dev_dbg(dev, "%s()\n", __func__);

    spin_lock_irqsave(&dev->power.lock, flags);

    if (!td->constraint_changed) {
        bool ret = td->cached_stop_ok;

        spin_unlock_irqrestore(&dev->power.lock, flags);
        return ret;
    }
    td->constraint_changed = false;
    td->cached_stop_ok = false;
    td->effective_constraint_ns = -1;
    constraint_ns = __dev_pm_qos_read_value(dev);

    spin_unlock_irqrestore(&dev->power.lock, flags);

    if (constraint_ns < 0)
        return false;

    constraint_ns *= NSEC_PER_USEC;
    /*
     * We can walk the children without any additional locking, because
     * they all have been suspended at this point and their
     * effective_constraint_ns fields won't be modified in parallel with us.
     */
    if (!dev->power.ignore_children)
        device_for_each_child(dev, &constraint_ns,
                      dev_update_qos_constraint);

    if (constraint_ns > 0) {
        constraint_ns -= td->start_latency_ns;
        if (constraint_ns == 0)
            return false;
    }
    td->effective_constraint_ns = constraint_ns;
    td->cached_stop_ok = constraint_ns > td->stop_latency_ns ||
                constraint_ns == 0;
    /*
     * The children have been suspended already, so we don't need to take
     * their stop latencies into account here.
     */
    return td->cached_stop_ok;
}

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_off_time_ns;
    s64 off_on_time_ns;

    if (genpd->max_off_time_changed) {
        struct gpd_link *link;

        /*
         * We have to invalidate the cached results for the masters, so
         * use the observation that default_power_down_ok() is not
         * going to be called for any master until this instance
         * returns.
         */
        list_for_each_entry(link, &genpd->slave_links, slave_node)
            link->master->max_off_time_changed = true;

        genpd->max_off_time_changed = false;
        genpd->cached_power_down_ok = false;
        genpd->max_off_time_ns = -1;
    } else {
        return genpd->cached_power_down_ok;
    }

    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;
    }

    min_off_time_ns = -1;
    /*
     * 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;

        /*
         * 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;

        if (min_off_time_ns > sd_max_off_ns || min_off_time_ns < 0)
            min_off_time_ns = sd_max_off_ns;
    }

    /*
     * Check if the devices in the domain can be off enough time.
     */
    list_for_each_entry(pdd, &genpd->dev_list, list_node) {
        struct gpd_timing_data *td;
        s64 constraint_ns;

        if (!pdd->dev->driver)
            continue;

        /*
         * Check if the device is allowed to be off long enough for the
         * domain to turn off and on (that's how much time it will
         * have to wait worst case).
         */
        td = &to_gpd_data(pdd)->td;
        constraint_ns = td->effective_constraint_ns;
        /* default_stop_ok() need not be called before us. */
        if (constraint_ns < 0) {
            constraint_ns = dev_pm_qos_read_value(pdd->dev);
            constraint_ns *= NSEC_PER_USEC;
        }
        if (constraint_ns == 0)
            continue;

        /*
         * constraint_ns cannot be negative here, because the device has
         * been suspended.
         */
        constraint_ns -= td->restore_state_latency_ns;
        if (constraint_ns <= off_on_time_ns)
            return false;

        if (min_off_time_ns > constraint_ns || min_off_time_ns < 0)
            min_off_time_ns = constraint_ns;
    }

    genpd->cached_power_down_ok = true;

    /*
     * If the computed minimum device off time is negative, there are no
     * latency constraints, so the domain can spend arbitrary time in the
     * "off" state.
     */
    if (min_off_time_ns < 0)
        return true;

    /*
     * The difference between the computed minimum subdomain or device off
     * time and the time needed to turn the domain on is the maximum
     * theoretical time this domain can spend in the "off" state.
     */
    genpd->max_off_time_ns = min_off_time_ns - genpd->power_on_latency_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,
};

struct dev_power_governor pm_domain_always_on_gov = {
    .power_down_ok = always_on_power_down_ok,
    .stop_ok = default_stop_ok,
};