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    Subject[RFC/RFT][PATCH v2 3/7] PM / sleep: Make async suspend/resume of devices use device links
    Date
    From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

    Make the device suspend/resume part of the core system
    suspend/resume code use device links to ensure that supplier
    and consumer devices will be suspended and resumed in the right
    order in case of async suspend/resume.

    The idea, roughly, is to use dpm_wait() to wait for all consumers
    before a supplier device suspend and to wait for all suppliers
    before a consumer device resume.

    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    ---
    drivers/base/base.h | 2 +
    drivers/base/core.c | 4 +-
    drivers/base/power/main.c | 68 +++++++++++++++++++++++++++++++++++++++++-----
    3 files changed, 66 insertions(+), 8 deletions(-)

    Index: linux-pm/drivers/base/base.h
    ===================================================================
    --- linux-pm.orig/drivers/base/base.h
    +++ linux-pm/drivers/base/base.h
    @@ -163,3 +163,5 @@ extern void device_links_driver_gone(str
    extern void device_links_no_driver(struct device *dev);
    extern bool device_links_busy(struct device *dev);
    extern void device_links_unbind_consumers(struct device *dev);
    +extern int device_links_read_lock(void);
    +extern void device_links_read_unlock(int idx);
    Index: linux-pm/drivers/base/core.c
    ===================================================================
    --- linux-pm.orig/drivers/base/core.c
    +++ linux-pm/drivers/base/core.c
    @@ -198,12 +198,12 @@ void device_link_del(struct device_link
    }
    EXPORT_SYMBOL_GPL(device_link_del);

    -static int device_links_read_lock(void)
    +int device_links_read_lock(void)
    {
    return srcu_read_lock(&device_links_srcu);
    }

    -static void device_links_read_unlock(int idx)
    +void device_links_read_unlock(int idx)
    {
    return srcu_read_unlock(&device_links_srcu, idx);
    }
    Index: linux-pm/drivers/base/power/main.c
    ===================================================================
    --- linux-pm.orig/drivers/base/power/main.c
    +++ linux-pm/drivers/base/power/main.c
    @@ -244,6 +244,62 @@ static void dpm_wait_for_children(struct
    device_for_each_child(dev, &async, dpm_wait_fn);
    }

    +static void dpm_wait_for_suppliers(struct device *dev, bool async)
    +{
    + struct device_link *link;
    + int idx;
    +
    + idx = device_links_read_lock();
    +
    + /*
    + * If the supplier goes away right after we've checked the link to it,
    + * we'll wait for its completion to change the state, but that's fine,
    + * because the only things that will block as a result are the SRCU
    + * callbacks freeing the link objects for the links in the list we're
    + * walking.
    + */
    + list_for_each_entry_rcu(link, &dev->links_to_suppliers, c_node)
    + if (link->status != DEVICE_LINK_DORMANT)
    + dpm_wait(link->supplier, async);
    +
    + device_links_read_unlock(idx);
    +}
    +
    +static void dpm_wait_for_superior(struct device *dev, bool async)
    +{
    + dpm_wait(dev->parent, async);
    + dpm_wait_for_suppliers(dev, async);
    +}
    +
    +static void dpm_wait_for_consumers(struct device *dev, bool async)
    +{
    + struct device_link *link;
    + int idx;
    +
    + idx = device_links_read_lock();
    +
    + /*
    + * The status of a device link can only be changed from "dormant" by a
    + * probe, but that cannot happen during system suspend/resume. In
    + * theory it can change to "dormant" at that time, but then it is
    + * reasonable to wait for the target device anyway (eg. if it goes
    + * away, it's better to wait for it to go away completely and then
    + * continue instead of trying to continue in parallel with its
    + * unregistration).
    + */
    + list_for_each_entry_rcu(link, &dev->links_to_consumers, s_node)
    + if (link->status != DEVICE_LINK_DORMANT)
    + dpm_wait(link->consumer, async);
    +
    + device_links_read_unlock(idx);
    +}
    +
    +static void dpm_wait_for_subordinate(struct device *dev, bool async)
    +{
    + dpm_wait_for_children(dev, async);
    + dpm_wait_for_consumers(dev, async);
    +}
    +
    /**
    * pm_op - Return the PM operation appropriate for given PM event.
    * @ops: PM operations to choose from.
    @@ -488,7 +544,7 @@ static int device_resume_noirq(struct de
    if (!dev->power.is_noirq_suspended)
    goto Out;

    - dpm_wait(dev->parent, async);
    + dpm_wait_for_superior(dev, async);

    if (dev->pm_domain) {
    info = "noirq power domain ";
    @@ -618,7 +674,7 @@ static int device_resume_early(struct de
    if (!dev->power.is_late_suspended)
    goto Out;

    - dpm_wait(dev->parent, async);
    + dpm_wait_for_superior(dev, async);

    if (dev->pm_domain) {
    info = "early power domain ";
    @@ -750,7 +806,7 @@ static int device_resume(struct device *
    goto Complete;
    }

    - dpm_wait(dev->parent, async);
    + dpm_wait_for_superior(dev, async);
    dpm_watchdog_set(&wd, dev);
    device_lock(dev);

    @@ -1038,7 +1094,7 @@ static int __device_suspend_noirq(struct
    if (dev->power.syscore || dev->power.direct_complete)
    goto Complete;

    - dpm_wait_for_children(dev, async);
    + dpm_wait_for_subordinate(dev, async);

    if (dev->pm_domain) {
    info = "noirq power domain ";
    @@ -1185,7 +1241,7 @@ static int __device_suspend_late(struct
    if (dev->power.syscore || dev->power.direct_complete)
    goto Complete;

    - dpm_wait_for_children(dev, async);
    + dpm_wait_for_subordinate(dev, async);

    if (dev->pm_domain) {
    info = "late power domain ";
    @@ -1358,7 +1414,7 @@ static int __device_suspend(struct devic
    TRACE_DEVICE(dev);
    TRACE_SUSPEND(0);

    - dpm_wait_for_children(dev, async);
    + dpm_wait_for_subordinate(dev, async);

    if (async_error)
    goto Complete;
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