Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

Jacob Pan
2014-05-14T22:24:24Z

On Tue, 13 May 2014 03:10:19 +0200
"Rafael J. Wysocki" <rjw@rjwysocki.net> wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Currently, some subsystems (e.g. PCI and the ACPI PM domain) have to
> resume all runtime-suspended devices during system suspend, mostly
> because those devices may need to be reprogrammed due to different
> wakeup settings for system sleep and for runtime PM.
>
> For some devices, though, it's OK to remain in runtime suspend
> throughout a complete system suspend/resume cycle (if the device was
> in runtime suspend at the start of the cycle). We would like to do
> this whenever possible, to avoid the overhead of extra power-up and
> power-down events.
>
> However, problems may arise because the device's descendants may
> require it to be at full power at various points during the cycle.
> Therefore the most straightforward way to do this safely is if the
> device and all its descendants can remain runtime suspended until the
> complete stage of system resume.
>
> To this end, introduce a new device PM flag, power.direct_complete
> and modify the PM core to use that flag as follows.
>
> If the ->prepare() callback of a device returns a positive number,
> the PM core will regard that as an indication that it may leave the
> device runtime-suspended. It will then check if the system power
> transition in progress is a suspend (and not hibernation in
> particular) and if the device is, indeed, runtime-suspended. In that
> case, the PM core will set the device's power.direct_complete flag.
> Otherwise it will clear power.direct_complete for the device and it
> also will later clear it for the device's parent (if there's one).
>
> Next, the PM core will not invoke the ->suspend() ->suspend_late(),
> ->suspend_irq(), ->resume_irq(), ->resume_early(), or ->resume()
> callbacks for all devices having power.direct_complete set. It
> will invoke their ->complete() callbacks, however, and those
> callbacks are then responsible for resuming the devices as
> appropriate, if necessary.
>
> Changelog partly based on an Alan Stern's description of the idea
> (http://marc.info/?l=linux-pm&m=139940466625569&w=2).
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/base/power/main.c | 45
> ++++++++++++++++++++++++++++-----------------
> include/linux/pm.h | 1 + 2 files changed, 29 insertions(+),
> 17 deletions(-)
>
> Index: linux-pm/include/linux/pm.h
> ===================================================================
> --- linux-pm.orig/include/linux/pm.h
> +++ linux-pm/include/linux/pm.h
> @@ -546,6 +546,7 @@ struct dev_pm_info {
> bool is_late_suspended:1;
> bool ignore_children:1;
> bool early_init:1; /* Owned by
> the PM core */
> + bool direct_complete:1; /*
> Owned by the PM core */ spinlock_t lock;
> #ifdef CONFIG_PM_SLEEP
> struct list_head entry;
> Index: linux-pm/drivers/base/power/main.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/main.c
> +++ linux-pm/drivers/base/power/main.c
> @@ -479,7 +479,7 @@ static int device_resume_noirq(struct de
> TRACE_DEVICE(dev);
> TRACE_RESUME(0);
>
> - if (dev->power.syscore)
> + if (dev->power.syscore || dev->power.direct_complete)
> goto Out;
>
> if (!dev->power.is_noirq_suspended)
> @@ -605,7 +605,7 @@ static int device_resume_early(struct de
> TRACE_DEVICE(dev);
> TRACE_RESUME(0);
>
> - if (dev->power.syscore)
> + if (dev->power.syscore || dev->power.direct_complete)
> goto Out;
>
> if (!dev->power.is_late_suspended)
> @@ -732,7 +732,7 @@ static int device_resume(struct device *
> TRACE_DEVICE(dev);
> TRACE_RESUME(0);
>
> - if (dev->power.syscore)
> + if (dev->power.syscore || dev->power.direct_complete)
> goto Complete;
>
> dpm_wait(dev->parent, async);
> @@ -1007,7 +1007,7 @@ static int __device_suspend_noirq(struct
> goto Complete;
> }
>
> - if (dev->power.syscore)
> + if (dev->power.syscore || dev->power.direct_complete)
> goto Complete;
>
> dpm_wait_for_children(dev, async);
> @@ -1146,7 +1146,7 @@ static int __device_suspend_late(struct
> goto Complete;
> }
>
> - if (dev->power.syscore)
> + if (dev->power.syscore || dev->power.direct_complete)
> goto Complete;
>
> dpm_wait_for_children(dev, async);
> @@ -1312,7 +1312,7 @@ static int __device_suspend(struct devic
>
> dpm_wait_for_children(dev, async);
>
> - if (async_error || dev->power.syscore)
> + if (async_error || dev->power.syscore ||
> dev->power.direct_complete) goto Complete;
>
> dpm_watchdog_set(&wd, dev);
> @@ -1365,10 +1365,19 @@ static int __device_suspend(struct devic
>
> End:
> if (!error) {
> + struct device *parent = dev->parent;
> +
> dev->power.is_suspended = true;
> - if (dev->power.wakeup_path
> - && dev->parent
> && !dev->parent->power.ignore_children)
> - dev->parent->power.wakeup_path = true;
> + if (parent) {
> + spin_lock_irq(&parent->power.lock);
> +
> + dev->parent->power.direct_complete = false;
should we respect ignore_children flag here? not all parent devices
create children with proper .prepare() function. this allows parents
override children.
I am looking at USB, a USB device could have logical children such as
ep_xx, they don't go through the same subsystem .prepare().

> + if (dev->power.wakeup_path
> + && !dev->parent->power.ignore_children)
> + dev->parent->power.wakeup_path =
> true; +
> + spin_unlock_irq(&parent->power.lock);
> + }
> }
>
> device_unlock(dev);
> @@ -1470,7 +1479,7 @@ static int device_prepare(struct device
> {
> int (*callback)(struct device *) = NULL;
> char *info = NULL;
> - int error = 0;
> + int ret = 0;
>
> if (dev->power.syscore)
> return 0;
> @@ -1518,17 +1527,19 @@ static int device_prepare(struct device
> callback = dev->driver->pm->prepare;
> }
>
> - if (callback) {
> - error = callback(dev);
> - suspend_report_result(callback, error);
> - }
> + if (callback)
> + ret = callback(dev);
>
> device_unlock(dev);
>
> - if (error)
> + if (ret < 0) {
> + suspend_report_result(callback, ret);
> pm_runtime_put(dev);
> -
> - return error;
> + return ret;
> + }
> + dev->power.direct_complete = ret > 0 && state.event ==
> PM_EVENT_SUSPEND
> + && pm_runtime_suspended(dev);
> + return 0;
> }
>
> /**
>
> --
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[Jacob Pan]