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    SubjectRe: [PATCH 2/8] PM: Asynchronous suspend and resume of devices
    Date
    [CC list trimmed.]

    On Sunday 24 January 2010, Alan Stern wrote:
    > On Sun, 24 Jan 2010, Rafael J. Wysocki wrote:
    >
    > > The async threads started for different devices as a result of
    > > calling async_schedule() are synchronized with each other and with
    > > the main suspend/resume thread with the help of completions, in the
    > > following way:
    > > (1) There is a completion, power.completion, for each device object.
    > > (2) Each device's completion is reset before calling async_schedule()
    > > for the device or, in the case of devices with the
    > > power.async_suspend flags unset, before executing the device's
    > > suspend and resume callbacks.
    > > (3) During suspend, right before running the bus type, device type
    > > and device class suspend callbacks for the device, the PM core
    > > waits for the completions of all the device's children to be
    > > completed.
    > > (4) During resume, right before running the bus type, device type and
    > > device class resume callbacks for the device, the PM core waits
    > > for the completion of the device's parent to be completed.
    > > (5) The PM core completes power.completion for each device right
    > > after the bus type, device type and device class suspend (or
    > > resume) callbacks executed for the device have returned.
    >
    > ...
    >
    > > /**
    > > + * dpm_wait - Wait for a PM operation to complete.
    > > + * @dev: Device to wait for.
    > > + * @async: If unset, wait only if the device's power.async_suspend flag is set.
    > > + */
    > > +static void dpm_wait(struct device *dev, bool async)
    > > +{
    > > + if (!dev)
    > > + return;
    > > +
    > > + if (async || dev->power.async_suspend)
    > > + wait_for_completion(&dev->power.completion);
    > > +}
    >
    > There needs to be a public interface to this function available for
    > drivers that have non-tree constraints. The arguments should be the
    > device to wait for and the device doing the waiting (needed only to
    > determine whether the caller is running synchronously or not).

    Something like the patch below?

    > This will be necessary for USB. In fact, your current code (with patch
    > 7/8 applied) is subject to a race that will sometimes cause a
    > non-high-speed USB device to fail to resume from hibernation.

    That's the kind of information I need at this point. What exactly should be
    added to patch 7/8 to avoid this problem?

    Rafael

    ---
    drivers/base/power/main.c | 11 +++++++++++
    include/linux/pm.h | 2 ++
    2 files changed, 13 insertions(+)

    Index: linux-2.6/drivers/base/power/main.c
    ===================================================================
    --- linux-2.6.orig/drivers/base/power/main.c
    +++ linux-2.6/drivers/base/power/main.c
    @@ -1050,3 +1050,14 @@ void __suspend_report_result(const char
    printk(KERN_ERR "%s(): %pF returns %d\n", function, fn, ret);
    }
    EXPORT_SYMBOL_GPL(__suspend_report_result);
    +
    +/**
    + * device_pm_wait_for_dev - Wait for suspend/resume of a device to complete.
    + * @dev: Device to wait for.
    + * @subordinate: Device that needs to wait for @dev.
    + */
    +void device_pm_wait_for_dev(struct device *subordinate, struct device *dev)
    +{
    + dpm_wait(dev, subordinate->power.async_suspend);
    +}
    +EXPORT_SYMBOL_GPL(device_pm_wait_for_dev);
    Index: linux-2.6/include/linux/pm.h
    ===================================================================
    --- linux-2.6.orig/include/linux/pm.h
    +++ linux-2.6/include/linux/pm.h
    @@ -512,6 +512,7 @@ extern void __suspend_report_result(cons
    __suspend_report_result(__func__, fn, ret); \
    } while (0)

    +extern void device_pm_wait_for_dev(struct device *sub, struct device *dev);
    #else /* !CONFIG_PM_SLEEP */

    #define device_pm_lock() do {} while (0)
    @@ -524,6 +525,7 @@ static inline int dpm_suspend_start(pm_m

    #define suspend_report_result(fn, ret) do {} while (0)

    +static inline void device_pm_wait_for_dev(struct device *a, struct device *b) {}
    #endif /* !CONFIG_PM_SLEEP */

    /* How to reorder dpm_list after device_move() */

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