Re: [PATCH 10/12] PM / core: Add LEAVE_SUSPENDED driver flag

[Ulf Hansson]

On 16 October 2017 at 03:30, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Define and document a new driver flag, DPM_FLAG_LEAVE_SUSPENDED, to
> instruct the PM core that it is desirable to leave the device in
> runtime suspend after system resume (for example, the device may be
> slow to resume and it may be better to avoid resuming it right away
> for this reason).
>
> Setting that flag causes the PM core to skip the ->resume_noirq,
> ->resume_early and ->resume callbacks for the device (like in the
> direct-complete optimization case) if (1) the wakeup settings of it
> are compatible with runtime PM (that is, either the device is
> configured to wake up the system from sleep or it cannot generate
> wakeup signals at all), and it will not be used for resuming any of
> its children or consumers.

As you state above, this looks like the direct_complete path, if being
used in conjunction with the DPM_SMART_SUSPEND flag.

Taking both these flags into account, what it seems to boils done is
that you need one flag, instructing the PM core to sometimes resume
the devices when it runs the direct_complete path, as isn't the case
today.

Wouldn't that be an alternative solution, which may be a bit simpler?

>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>  Documentation/driver-api/pm/devices.rst |   20 +++++++
>  drivers/base/power/main.c               |   81 ++++++++++++++++++++++++++++++--
>  include/linux/pm.h                      |   12 +++-
>  3 files changed, 104 insertions(+), 9 deletions(-)
>
> Index: linux-pm/include/linux/pm.h
> ===================================================================
> --- linux-pm.orig/include/linux/pm.h
> +++ linux-pm/include/linux/pm.h
> @@ -559,6 +559,7 @@ struct pm_subsys_data {
>   * NEVER_SKIP: Do not skip system suspend/resume callbacks for the device.
>   * SMART_PREPARE: Check the return value of the driver's ->prepare callback.
>   * SMART_SUSPEND: No need to resume the device from runtime suspend.
> + * LEAVE_SUSPENDED: Avoid resuming the device during system resume if possible.
>   *
>   * Setting SMART_PREPARE instructs bus types and PM domains which may want
>   * system suspend/resume callbacks to be skipped for the device to return 0 from
> @@ -573,10 +574,14 @@ struct pm_subsys_data {
>   * the "late" and "noirq" phases of device suspend for the device if it remains
>   * in runtime suspend at the beginning of the "late" phase (when runtime PM has
>   * been disabled for it).
> + *
> + * Setting LEAVE_SUSPENDED informs the PM core and middle layer code that the
> + * driver prefers the device to be left in runtime suspend after system resume.
>   */
> -#define DPM_FLAG_NEVER_SKIP    BIT(0)
> -#define DPM_FLAG_SMART_PREPARE BIT(1)
> -#define DPM_FLAG_SMART_SUSPEND BIT(2)
> +#define DPM_FLAG_NEVER_SKIP            BIT(0)
> +#define DPM_FLAG_SMART_PREPARE         BIT(1)
> +#define DPM_FLAG_SMART_SUSPEND         BIT(2)
> +#define DPM_FLAG_LEAVE_SUSPENDED       BIT(3)

I would appreciate if you could reformat the patches such that you
only have to add one line here.

It makes it easier when I later runs a "git blame" to understand what
commit that introduced each flag. :-)

>
>  struct dev_pm_info {
>         pm_message_t            power_state;
> @@ -598,6 +603,7 @@ struct dev_pm_info {
>         bool                    wakeup_path:1;
>         bool                    syscore:1;
>         bool                    no_pm_callbacks:1;      /* Owned by the PM core */
> +       unsigned int            must_resume:1;  /* Owned by the PM core */
>  #else
>         unsigned int            should_wakeup:1;
>  #endif
> Index: linux-pm/drivers/base/power/main.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/main.c
> +++ linux-pm/drivers/base/power/main.c
> @@ -705,6 +705,12 @@ static int device_resume_early(struct de
>         if (!dev->power.is_late_suspended)
>                 goto Out;
>
> +       if (dev_pm_test_driver_flags(dev, DPM_FLAG_LEAVE_SUSPENDED) &&
> +           !dev->power.must_resume) {
> +               pm_runtime_set_suspended(dev);
> +               goto Out;
> +       }
> +
>         dpm_wait_for_superior(dev, async);
>
>         if (dev->pm_domain) {
> @@ -1098,6 +1104,32 @@ static pm_message_t resume_event(pm_mess
>         return PMSG_ON;
>  }
>
> +static void dpm_suppliers_set_must_resume(struct device *dev)
> +{
> +       struct device_link *link;
> +       int idx;
> +
> +       idx = device_links_read_lock();
> +
> +       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
> +               link->supplier->power.must_resume = true;
> +
> +       device_links_read_unlock(idx);
> +}
> +
> +static void dpm_leave_suspended(struct device *dev)
> +{
> +       pm_runtime_set_suspended(dev);
> +       dev->power.is_suspended = false;
> +       dev->power.is_late_suspended = false;
> +       /*
> +        * This tells middle layer code to schedule runtime resume of the device
> +        * from its ->complete callback to update the device's power state in
> +        * case the platform firmware has been involved in resuming the system.
> +        */
> +       dev->power.direct_complete = true;
> +}
> +
>  /**
>   * __device_suspend_noirq - Execute a "noirq suspend" callback for given device.
>   * @dev: Device to handle.
> @@ -1135,8 +1167,20 @@ static int __device_suspend_noirq(struct
>          * the callback invocation for them.
>          */
>         if (dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) &&
> -           pm_runtime_status_suspended(dev))
> -               goto Skip;
> +           pm_runtime_status_suspended(dev)) {
> +               /*
> +                * The device may be left suspended during system resume if
> +                * that is preferred by its driver and it will not be used for
> +                * resuming any of its children or consumers.
> +                */
> +               if (dev_pm_test_driver_flags(dev, DPM_FLAG_LEAVE_SUSPENDED) &&
> +                   !dev->power.must_resume) {
> +                       dpm_leave_suspended(dev);
> +                       goto Complete;
> +               } else {
> +                       goto Skip;
> +               }
> +       }
>
>         if (dev->pm_domain) {
>                 info = "noirq power domain ";
> @@ -1163,6 +1207,28 @@ static int __device_suspend_noirq(struct
>                 goto Complete;
>         }
>
> +       /*
> +        * The device may be left suspended during system resume if that is
> +        * preferred by its driver and its wakeup configuration is compatible
> +        * with runtime PM, and it will not be used for resuming any of its
> +        * children or consumers.
> +        */
> +       if (dev_pm_test_driver_flags(dev, DPM_FLAG_LEAVE_SUSPENDED) &&
> +           (device_may_wakeup(dev) || !device_can_wakeup(dev)) &&
> +           !dev->power.must_resume) {
> +               dpm_leave_suspended(dev);
> +               goto Complete;
> +       }
> +
> +       /*
> +        * The parent and suppliers will be necessary to resume the device
> +        * during system resume, so avoid leaving them in runtime suspend.
> +        */
> +       if (dev->parent)
> +               dev->parent->power.must_resume = true;
> +
> +       dpm_suppliers_set_must_resume(dev);
> +
>  Skip:
>         dev->power.is_noirq_suspended = true;
>
> @@ -1698,8 +1764,9 @@ static int device_prepare(struct device
>         if (dev->power.syscore)
>                 return 0;
>
> -       WARN_ON(dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) &&
> -               !pm_runtime_enabled(dev));
> +       WARN_ON(!pm_runtime_enabled(dev) &&
> +               dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND |
> +                                             DPM_FLAG_LEAVE_SUSPENDED));
>
>         /*
>          * If a device's parent goes into runtime suspend at the wrong time,
> @@ -1712,6 +1779,12 @@ static int device_prepare(struct device
>         device_lock(dev);
>
>         dev->power.wakeup_path = device_may_wakeup(dev);
> +       /*
> +        * Avoid leaving devices in suspend after transitions that don't really
> +        * suspend them in general.
> +        */
> +       dev->power.must_resume = state.event == PM_EVENT_FREEZE ||
> +                               state.event == PM_EVENT_QUIESCE;
>
>         if (dev->power.no_pm_callbacks) {
>                 ret = 1;        /* Let device go direct_complete */
> Index: linux-pm/Documentation/driver-api/pm/devices.rst
> ===================================================================
> --- linux-pm.orig/Documentation/driver-api/pm/devices.rst
> +++ linux-pm/Documentation/driver-api/pm/devices.rst
> @@ -785,6 +785,22 @@ means that they should be put into the f
>
>  During system-wide resume from a sleep state it's easiest to put devices into
>  the full-power state, as explained in :file:`Documentation/power/runtime_pm.txt`.
> -Refer to that document for more information regarding this particular issue as
> +[Refer to that document for more information regarding this particular issue as
>  well as for information on the device runtime power management framework in
> -general.
> +general.]
> +
> +However, it may be desirable to leave some devices in runtime suspend after
> +system resume and device drivers can use the ``DPM_FLAG_LEAVE_SUSPENDED`` flag
> +to indicate to the PM core that this is the case.  If that flag is set for a
> +device and the wakeup settings of it are compatible with runtime PM (that is,
> +either the device is configured to wake up the system from sleep or it cannot
> +generate wakeup signals at all), and it will not be used for resuming any of its
> +children or consumers, the PM core will skip all of the system resume callbacks
> +in the ``resume_noirq``, ``resume_early`` and ``resume`` phases for it and its
> +runtime power management status will be set to "suspended".
> +
> +Still, if the platform firmware is involved in the handling of system resume, it
> +may change the state of devices in unpredictable ways, so in that case the
> +middle layer code (for example, a bus type or PM domain) the driver works with
> +should update the device's power state and schedule runtime resume of it to
> +align its power settings with the expectations of the runtime PM framework.
>
>

Regarding the DPM_NEVER_SKIP flag, is that flag only to prevent
direct_complete, and thus it ought not to be used with these other
driver PM flags that you add in this series?

Have you considered that DPM_NEVER_SKIP also propagates to parents
etc? Just to make sure one you won't skip invoking some system sleep
callbacks, even if they should because a child requires it?

Or maybe I am just tired and should continue to review with a more
fresh mind. :-)

Kind regards
Uffe