On Monday, August 06, 2012, Alan Stern wrote:
> On Sun, 5 Aug 2012, Rafael J. Wysocki wrote:
[...]
>
> > What about the appended experimental patch?
>
> For now, I think it would be best to start with a single func argument.
> If it turns out that anyone really needs to have two separate
> arguments, the single-argument form can be reimplemented on top of the
> two-argument form easily enough.
All right.
> > @@ -484,6 +484,15 @@ static int rpm_suspend(struct device *de
> > goto out;
> > }
> >
> > +void rpm_queue_up_resume(struct device *dev)
> > +{
> > + dev->power.request = RPM_REQ_RESUME;
> > + if (!dev->power.request_pending) {
> > + dev->power.request_pending = true;
> > + queue_work(pm_wq, &dev->power.work);
> > + }
> > +}
> > +
> > /**
> > * rpm_resume - Carry out runtime resume of given device.
> > * @dev: Device to resume.
> > @@ -524,7 +533,9 @@ static int rpm_resume(struct device *dev
> > * rather than cancelling it now only to restart it again in the near
> > * future.
> > */
> > - dev->power.request = RPM_REQ_NONE;
> > + if (dev->power.request != RPM_REQ_RESUME || !dev->power.func)
> > + dev->power.request = RPM_REQ_NONE;
> > +
> > if (!dev->power.timer_autosuspends)
> > pm_runtime_deactivate_timer(dev);
> >
> > @@ -533,6 +544,12 @@ static int rpm_resume(struct device *dev
> > goto out;
> > }
> >
> > + if (dev->power.func && (rpmflags & RPM_ASYNC)) {
> > + rpm_queue_up_resume(dev);
> > + retval = 0;
> > + goto out;
> > + }
> > +
> > if (dev->power.runtime_status == RPM_RESUMING
> > || dev->power.runtime_status == RPM_SUSPENDING) {
> > DEFINE_WAIT(wait);
>
> All those changes (and some of the following ones) are symptoms of a
> basic mistake in this approach.
Every time you say something like this (i.e. liks someone who knows better)
I kind of feel like being under attach, which I hope is not your intention.
Never mind. :-)
Those changes are there for different reasons rather unrelated to the way
func() is being called, so let me explain.
First, rpm_queue_up_resume() is introduced, because the code it contains will
have to be called in two different places. At least I don't see how to avoid
that without increasing the code complexity too much.
Second, the following change in rpm_resume()
- dev->power.request = RPM_REQ_NONE;
+ if (dev->power.request != RPM_REQ_RESUME || !dev->power.func)
+ dev->power.request = RPM_REQ_NONE;
is made to prevent rpm_resume() from canceling the execution of func() queued
up by an earlier pm_runtime_get_and_call(). I believe it is necessary.
Finally, this change in rpm_resume():
+ if (dev->power.func && (rpmflags & RPM_ASYNC)) {
+ rpm_queue_up_resume(dev);
+ retval = 0;
+ goto out;
+ }
is not strictly necessary if pm_runtime_get_and_call() is modified to run
rpm_queue_up_resume() directly, like in the new version of the patch which is
appended. This reduces the number of checks overall, so perhaps it's better.
> The idea of this new feature is to
> call "func" as soon as we know the device is at full power, no matter
> how it got there.
Yes, it is so.
> That means we should call it near the end of
> rpm_resume() (just before the rpm_idle() call), not from within
> pm_runtime_work().
>
> Doing it this way will be more efficient and (I think) will remove
> some races.
Except that func() shouldn't be executed under dev->power.lock, which makes it
rather difficult to call it from rpm_resume(). Or at least it seems so.
Moreover, it should be called after we've changed the status to RPM_ACTIVE
_and_ dropped the lock.
Besides, I'd like to know what races you're referring to (perhaps you're seeing
some more of them than I am).
> > @@ -877,6 +903,48 @@ int __pm_runtime_resume(struct device *d
> > }
> > EXPORT_SYMBOL_GPL(__pm_runtime_resume);
> >
> > +int pm_runtime_get_and_call(struct device *dev, void (*func)(struct device
> > *),
> > + void (*func_async)(struct device *))
> > +{
> > + unsigned long flags;
> > + int ret;
> > +
> > + atomic_inc(&dev->power.usage_count);
> > +
> > + spin_lock_irqsave(&dev->power.lock, flags);
> > +
> > + ret = dev->power.runtime_error;
> > + if (ret) {
> > + func = NULL;
> > + goto out;
> > + }
> > +
> > + if (dev->power.runtime_status != RPM_ACTIVE
> > + && dev->power.disable_depth == 0)
> > + func = NULL;
> > +
> > + if (!func && func_async) {
> > + if (dev->power.func) {
> > + ret = -EAGAIN;
> > + goto out;
> > + } else {
> > + dev->power.func = func_async;
> > + }
> > + }
>
> The logic here is kind of hard to follow. It will be simpler when
> there's only one "func":
>
> If the status is RPM_ACTIVE or disable_depth > 0 then
> call "func" directly.
>
> Otherwise save "func" in dev.power and do an async resume.
Yeah. But do not run func() under power.lock, right?
> Some more things:
>
> In __pm_runtime_set_status(), if power.func is set then I think we
> should call it if the new status is ACTIVE.
__pm_runtime_set_status() only works if power.disable_depth > 0, in
which case func() will be called synchronously. Now, if someone does
pm_runtime_get_and_call() immediately followed by pm_runtime_disable()
(perhaps from a different thread), then __pm_runtime_disable() will
resume the device, so it's better to call func() from there if set,
I think. And clear power.func afterwards.
> Likwise at the end of rpm_suspend(), if the suspend fails.
The only way by which power.func can be different from NULL at that point
is when the work item queued up by pm_runtime_get_and_call() runs after
rpm_suspend() has changed the status to RPM_SUSPENDING. However in that
case the rpm_resume(dev, 0) in pm_runtime_work() will wait for the
suspend to complete (or fail) and func() will be run when it returns.
> There should be an invariant: Whenever the status is RPM_ACTIVE,
> power.func must be NULL.
Well, maybe so, but I don't see why right now.
> pm_runtime_barrier() should always clear power.func, even if the
> rpm_resume() call fails.
Wouldn't it be better to wait for func() to be run?
> The documentation should explain that in some ways, "func" is like a
> workqueue callback routine: Subsystems and drivers have to be careful
> to make sure that it can't be invoked after the device is unbound. A
> safe way to do this is to call pm_runtime_barrier() from within the
> driver's .remove() routine, after making sure that
> pm_runtime_get_and_call() won't be invoked any more.
Sure.
The appended patch doesn't contain any changes in __pm_runtime_disable()
or pm_runtime_barrier(), but you are right that they are necessary.
Thanks,
Rafael
---
drivers/base/power/runtime.c | 98 ++++++++++++++++++++++++++++++++++++++-----
include/linux/pm.h | 1
include/linux/pm_runtime.h | 11 ++++
3 files changed, 99 insertions(+), 11 deletions(-)
Index: linux/drivers/base/power/runtime.c
===================================================================
--- linux.orig/drivers/base/power/runtime.c
+++ linux/drivers/base/power/runtime.c
@@ -484,6 +484,15 @@ static int rpm_suspend(struct device *de
goto out;
}
+void rpm_queue_up_resume(struct device *dev)
+{
+ dev->power.request = RPM_REQ_RESUME;
+ if (!dev->power.request_pending) {
+ dev->power.request_pending = true;
+ queue_work(pm_wq, &dev->power.work);
+ }
+}
+
/**
* rpm_resume - Carry out runtime resume of given device.
* @dev: Device to resume.
@@ -519,12 +528,18 @@ static int rpm_resume(struct device *dev
goto out;
/*
- * Other scheduled or pending requests need to be canceled. Small
- * optimization: If an autosuspend timer is running, leave it running
- * rather than cancelling it now only to restart it again in the near
- * future.
+ * Other scheduled or pending requests need to be canceled. If the
+ * execution of a function is queued up along with a resume request,
+ * do not cancel it.
+ */
+ if (dev->power.request != RPM_REQ_RESUME || !dev->power.func)
+ dev->power.request = RPM_REQ_NONE;
+
+ /*
+ * Small optimization: If an autosuspend timer is running, leave it
+ * running rather than cancelling it now only to restart it again in the
+ * near future.
*/
- dev->power.request = RPM_REQ_NONE;
if (!dev->power.timer_autosuspends)
pm_runtime_deactivate_timer(dev);
@@ -591,11 +606,7 @@ static int rpm_resume(struct device *dev
/* Carry out an asynchronous or a synchronous resume. */
if (rpmflags & RPM_ASYNC) {
- dev->power.request = RPM_REQ_RESUME;
- if (!dev->power.request_pending) {
- dev->power.request_pending = true;
- queue_work(pm_wq, &dev->power.work);
- }
+ rpm_queue_up_resume(dev);
retval = 0;
goto out;
}
@@ -691,6 +702,7 @@ static int rpm_resume(struct device *dev
static void pm_runtime_work(struct work_struct *work)
{
struct device *dev = container_of(work, struct device, power.work);
+ void (*func)(struct device *) = NULL;
enum rpm_request req;
spin_lock_irq(&dev->power.lock);
@@ -715,12 +727,24 @@ static void pm_runtime_work(struct work_
rpm_suspend(dev, RPM_NOWAIT | RPM_AUTO);
break;
case RPM_REQ_RESUME:
- rpm_resume(dev, RPM_NOWAIT);
+ func = dev->power.func;
+ if (func) {
+ dev->power.func = NULL;
+ pm_runtime_get_noresume(dev);
+ rpm_resume(dev, 0);
+ } else {
+ rpm_resume(dev, RPM_NOWAIT);
+ }
break;
}
out:
spin_unlock_irq(&dev->power.lock);
+
+ if (func) {
+ func(dev);
+ pm_runtime_put(dev);
+ }
}
/**
@@ -877,6 +901,58 @@ int __pm_runtime_resume(struct device *d
}
EXPORT_SYMBOL_GPL(__pm_runtime_resume);
+int pm_runtime_get_and_call(struct device *dev, void (*func)(struct device *))
+{
+ unsigned long flags;
+ bool sync = false;
+ int ret;
+
+ atomic_inc(&dev->power.usage_count);
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ ret = dev->power.runtime_error;
+ if (ret)
+ goto out;
+
+ sync = dev->power.runtime_status == RPM_ACTIVE
+ || dev->power.disable_depth > 0;
+
+ if (!sync) {
+ if (dev->power.func) {
+ ret = -EAGAIN;
+ goto out;
+ } else {
+ dev->power.func = func;
+ }
+ }
+
+ /*
+ * The approach here is the same as in rpm_suspend(): autosuspend timers
+ * will be activated shortly anyway, so it is pointless to cancel them
+ * now.
+ */
+ if (!dev->power.timer_autosuspends)
+ pm_runtime_deactivate_timer(dev);
+
+ if (sync)
+ dev->power.request = RPM_REQ_NONE;
+ else
+ rpm_queue_up_resume(dev);
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+
+ if (sync) {
+ if (func)
+ func(dev);
+
+ return 1;
+ }
+
+ return ret;
+}
+
/**
* __pm_runtime_set_status - Set runtime PM status of a device.
* @dev: Device to handle.
Index: linux/include/linux/pm.h
===================================================================
--- linux.orig/include/linux/pm.h
+++ linux/include/linux/pm.h
@@ -547,6 +547,7 @@ struct dev_pm_info {
unsigned long suspended_jiffies;
unsigned long accounting_timestamp;
struct dev_pm_qos_request *pq_req;
+ void (*func)(struct device *);
#endif
struct pm_subsys_data *subsys_data; /* Owned by the subsystem. */
struct pm_qos_constraints *constraints;
Index: linux/include/linux/pm_runtime.h
===================================================================
--- linux.orig/include/linux/pm_runtime.h
+++ linux/include/linux/pm_runtime.h
@@ -47,6 +47,8 @@ extern void pm_runtime_set_autosuspend_d
extern unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
extern void pm_runtime_update_max_time_suspended(struct device *dev,
s64 delta_ns);
+extern int pm_runtime_get_and_call(struct device *dev,
+ void (*func)(struct device *));
static inline bool pm_children_suspended(struct device *dev)
{
@@ -150,6 +152,15 @@ static inline void pm_runtime_set_autosu
static inline unsigned long pm_runtime_autosuspend_expiration(
struct device *dev) { return 0; }
+static inline int pm_runtime_get_and_call(struct device *dev,
+ void (*func)(struct device *))
+{
+ if (func)
+ func(dev);
+
+ return 1;
+}
+
#endif /* !CONFIG_PM_RUNTIME */
static inline int pm_runtime_idle(struct device *dev)
--
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