[PATCH] PM: runtime: Allow rpm_resume() to succeed when runtime PM is disabled
Ulf Hansson
ulf.hansson at linaro.org
Tue Nov 30 03:57:55 PST 2021
[...]
> > > > > >
> > > > > > Am I thinking correctly that this is mostly about working around the
> > > > > > limitations of pm_runtime_force_suspend()?
> > > > >
> > > > > No, this isn't related at all.
> > > > >
> > > > > The cpuidle-psci driver doesn't have PM callbacks, thus using
> > > > > pm_runtime_force_suspend() would not work here.
> > > >
> > > > Just wanted to send a ping on this to see if we can come to a
> > > > conclusion. Or maybe we did? :-)
> > > >
> > > > I think in the end, what slightly bothers me, is that the behavior is
> > > > a bit inconsistent. Although, maybe it's the best we can do.
> > >
> > > I've been thinking about this and it looks like we can do better, but
> > > instead of talking about this I'd rather send a patch.
> >
> > Alright.
> >
> > I was thinking along the lines of make similar changes for
> > rpm_idle|suspend(). That would make the behaviour even more
> > consistent, I think.
> >
> > Perhaps that's what you have in mind? :-)
>
> Well, not exactly.
>
> The idea is to add another counter (called restrain_depth in the patch)
> to prevent rpm_resume() from running the callback when that is potentially
> problematic. With that, it is possible to actually distinguish devices
> with PM-runtime enabled and it allows the PM-runtime status to be checked
> when it is still known to be meaningful.
Hmm, I don't quite understand the benefit of introducing a new flag
for this. rpm_resume() already checks the disable_depth to understand
when it's safe to invoke the callback. Maybe there is a reason why
that isn't sufficient?
>
> It requires quite a few changes, but is rather straightforward, unless I'm
> missing something.
>
> Please see the patch below. I've only checked that it builds on x86-64.
>
> ---
> drivers/base/power/main.c | 18 +++----
> drivers/base/power/runtime.c | 105 ++++++++++++++++++++++++++++++++++++-------
> include/linux/pm.h | 2
> include/linux/pm_runtime.h | 2
> 4 files changed, 101 insertions(+), 26 deletions(-)
>
> Index: linux-pm/include/linux/pm.h
> ===================================================================
> --- linux-pm.orig/include/linux/pm.h
> +++ linux-pm/include/linux/pm.h
> @@ -598,6 +598,7 @@ struct dev_pm_info {
> atomic_t usage_count;
> atomic_t child_count;
> unsigned int disable_depth:3;
> + unsigned int restrain_depth:3; /* PM core private */
> unsigned int idle_notification:1;
> unsigned int request_pending:1;
> unsigned int deferred_resume:1;
> @@ -609,6 +610,7 @@ struct dev_pm_info {
> unsigned int use_autosuspend:1;
> unsigned int timer_autosuspends:1;
> unsigned int memalloc_noio:1;
> + unsigned int already_suspended:1; /* PM core private */
> unsigned int links_count;
> enum rpm_request request;
> enum rpm_status runtime_status;
> Index: linux-pm/include/linux/pm_runtime.h
> ===================================================================
> --- linux-pm.orig/include/linux/pm_runtime.h
> +++ linux-pm/include/linux/pm_runtime.h
> @@ -46,6 +46,8 @@ extern void pm_runtime_enable(struct dev
> extern void __pm_runtime_disable(struct device *dev, bool check_resume);
> extern void pm_runtime_allow(struct device *dev);
> extern void pm_runtime_forbid(struct device *dev);
> +extern void pm_runtime_restrain(struct device *dev);
> +extern void pm_runtime_relinquish(struct device *dev);
> extern void pm_runtime_no_callbacks(struct device *dev);
> extern void pm_runtime_irq_safe(struct device *dev);
> extern void __pm_runtime_use_autosuspend(struct device *dev, bool use);
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -744,11 +744,11 @@ static int rpm_resume(struct device *dev
> repeat:
> if (dev->power.runtime_error)
> retval = -EINVAL;
> - else if (dev->power.disable_depth == 1 && dev->power.is_suspended
> - && dev->power.runtime_status == RPM_ACTIVE)
> - retval = 1;
> else if (dev->power.disable_depth > 0)
> retval = -EACCES;
> + else if (dev->power.restrain_depth > 0)
> + retval = dev->power.runtime_status == RPM_ACTIVE ? 1 : -EAGAIN;
> +
> if (retval)
> goto out;
>
> @@ -1164,9 +1164,9 @@ EXPORT_SYMBOL_GPL(pm_runtime_get_if_acti
> * @dev: Device to handle.
> * @status: New runtime PM status of the device.
> *
> - * If runtime PM of the device is disabled or its power.runtime_error field is
> - * different from zero, the status may be changed either to RPM_ACTIVE, or to
> - * RPM_SUSPENDED, as long as that reflects the actual state of the device.
> + * If runtime PM of the device is disabled or restrained, or its
> + * power.runtime_error field is nonzero, the status may be changed either to
> + * RPM_ACTIVE, or to RPM_SUSPENDED, as long as that reflects its actual state.
> * However, if the device has a parent and the parent is not active, and the
> * parent's power.ignore_children flag is unset, the device's status cannot be
> * set to RPM_ACTIVE, so -EBUSY is returned in that case.
> @@ -1195,13 +1195,16 @@ int __pm_runtime_set_status(struct devic
> spin_lock_irq(&dev->power.lock);
>
> /*
> - * Prevent PM-runtime from being enabled for the device or return an
> - * error if it is enabled already and working.
> + * Prevent PM-runtime from being used for the device or return an
> + * error if it is in use already.
> */
> - if (dev->power.runtime_error || dev->power.disable_depth)
> - dev->power.disable_depth++;
> - else
> + if (dev->power.runtime_error || dev->power.disable_depth ||
> + dev->power.restrain_depth) {
> + pm_runtime_get_noresume(dev);
Why do we need to bump the usage count here? Except for balancing with
pm_runtime_relinquish() a few lines below, of course?
> + dev->power.restrain_depth++;
> + } else {
> error = -EAGAIN;
> + }
>
> spin_unlock_irq(&dev->power.lock);
>
> @@ -1278,7 +1281,7 @@ int __pm_runtime_set_status(struct devic
> device_links_read_unlock(idx);
> }
>
> - pm_runtime_enable(dev);
> + pm_runtime_relinquish(dev);
>
> return error;
> }
> @@ -1513,6 +1516,72 @@ void pm_runtime_allow(struct device *dev
> EXPORT_SYMBOL_GPL(pm_runtime_allow);
>
> /**
> + * pm_runtime_restrain - Temporarily block runtime PM of a device.
> + * @dev: Device to handle.
> + *
> + * Increase the device's usage count and its restrain_dpeth count. If the
> + * latter was 0 initially, cancel the runtime PM work for @dev if pending and
> + * wait for all of the runtime PM operations on it in progress to complete.
> + *
> + * After this function has been called, attempts to runtime-suspend @dev will
> + * fail with -EAGAIN and attempts to runtime-resume it will succeed if its
> + * runtime PM status is RPM_ACTIVE and will fail with -EAGAIN otherwise.
> + *
> + * This function can only be called by the PM core.
> + */
> +void pm_runtime_restrain(struct device *dev)
> +{
> + pm_runtime_get_noresume(dev);
> +
> + spin_lock_irq(&dev->power.lock);
> +
> + if (dev->power.restrain_depth++ > 0)
> + goto out;
> +
> + if (dev->power.disable_depth > 0) {
> + dev->power.already_suspended = false;
> + goto out;
> + }
> +
> + /* Update time accounting before blocking PM-runtime. */
> + update_pm_runtime_accounting(dev);
> +
> + __pm_runtime_barrier(dev);
> +
> + dev->power.already_suspended = pm_runtime_status_suspended(dev);
> +
> +out:
> + spin_unlock_irq(&dev->power.lock);
> +}
What if someone calls pm_runtime_disable() after the PM core has
called pm_runtime_restrain() for a device? It looks like we may run
another round of __pm_runtime_barrier() and
update_pm_runtime_accounting(), does that really make sense?
> +
> +/**
> + * pm_runtime_relinquish - Unblock runtime PM of a device.
> + * @dev: Device to handle.
> + *
> + * Decrease the device's usage count and its restrain_dpeth count.
> + *
> + * This function can only be called by the PM core.
> + */
> +void pm_runtime_relinquish(struct device *dev)
> +{
> + spin_lock_irq(&dev->power.lock);
> +
> + if (dev->power.restrain_depth > 0) {
> + dev->power.restrain_depth--;
> +
> + /* About to unbolck runtime PM, set accounting_timestamp to now */
> + if (!dev->power.restrain_depth && !dev->power.disable_depth)
> + dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
> + } else {
> + dev_warn(dev, "Unbalanced %s!\n", __func__);
> + }
> +
> + spin_unlock_irq(&dev->power.lock);
> +
> + pm_runtime_put_noidle(dev);
> +}
> +
> +/**
> * pm_runtime_no_callbacks - Ignore runtime PM callbacks for a device.
> * @dev: Device to handle.
> *
> @@ -1806,8 +1875,10 @@ int pm_runtime_force_suspend(struct devi
> int (*callback)(struct device *);
> int ret;
>
> - pm_runtime_disable(dev);
> - if (pm_runtime_status_suspended(dev))
> + pm_runtime_restrain(dev);
> +
> + /* No suspend if the device has already been suspended by PM-runtime. */
> + if (!dev->power.already_suspended)
I assume you are looking at using pm_runtime_force_suspend|resume() to
support my use case for the cpuidle-psci driver? In other words,
replace pm_runtime_get_sync() and pm_runtime_put_sync_suspend() in
__psci_enter_domain_idle_state(), right?
If so, that doesn't really fit well, I think. Not only because we
don't have system suspend/resume callbacks available, which is really
the proper place to call the pm_runtime_force_*() functions from, but
also because we don't want to call __pm_runtime_barrier(), etc, every
time in the idle path of a CPU. If anything, we should instead strive
towards a more lightweight path than what we currently have.
> return 0;
>
> callback = RPM_GET_CALLBACK(dev, runtime_suspend);
> @@ -1832,7 +1903,7 @@ int pm_runtime_force_suspend(struct devi
> return 0;
>
> err:
> - pm_runtime_enable(dev);
> + pm_runtime_relinquish(dev);
> return ret;
> }
> EXPORT_SYMBOL_GPL(pm_runtime_force_suspend);
> @@ -1854,7 +1925,7 @@ int pm_runtime_force_resume(struct devic
> int (*callback)(struct device *);
> int ret = 0;
>
> - if (!pm_runtime_status_suspended(dev) || !dev->power.needs_force_resume)
> + if (!dev->power.already_suspended || !dev->power.needs_force_resume)
> goto out;
>
> /*
> @@ -1874,7 +1945,7 @@ int pm_runtime_force_resume(struct devic
> pm_runtime_mark_last_busy(dev);
> out:
> dev->power.needs_force_resume = 0;
> - pm_runtime_enable(dev);
> + pm_runtime_relinquish(dev);
> return ret;
> }
> EXPORT_SYMBOL_GPL(pm_runtime_force_resume);
> Index: linux-pm/drivers/base/power/main.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/main.c
> +++ linux-pm/drivers/base/power/main.c
> @@ -809,7 +809,7 @@ Skip:
> Out:
> TRACE_RESUME(error);
>
> - pm_runtime_enable(dev);
> + pm_runtime_relinquish(dev);
> complete_all(&dev->power.completion);
> return error;
> }
> @@ -907,8 +907,8 @@ static int device_resume(struct device *
> goto Complete;
>
> if (dev->power.direct_complete) {
> - /* Match the pm_runtime_disable() in __device_suspend(). */
> - pm_runtime_enable(dev);
> + /* Match the pm_runtime_restrict() in __device_suspend(). */
> + pm_runtime_relinquish(dev);
> goto Complete;
> }
>
> @@ -1392,7 +1392,7 @@ static int __device_suspend_late(struct
> TRACE_DEVICE(dev);
> TRACE_SUSPEND(0);
>
> - __pm_runtime_disable(dev, false);
> + pm_runtime_restrain(dev);
>
> dpm_wait_for_subordinate(dev, async);
>
> @@ -1627,9 +1627,9 @@ static int __device_suspend(struct devic
> * callbacks for it.
> *
> * If the system-wide suspend callbacks below change the configuration
> - * of the device, they must disable runtime PM for it or otherwise
> - * ensure that its runtime-resume callbacks will not be confused by that
> - * change in case they are invoked going forward.
> + * of the device, they must ensure that its runtime-resume callbacks
> + * will not be confused by that change in case they are invoked going
> + * forward.
> */
> pm_runtime_barrier(dev);
>
> @@ -1648,13 +1648,13 @@ static int __device_suspend(struct devic
>
> if (dev->power.direct_complete) {
> if (pm_runtime_status_suspended(dev)) {
> - pm_runtime_disable(dev);
> + pm_runtime_restrain(dev);
> if (pm_runtime_status_suspended(dev)) {
> pm_dev_dbg(dev, state, "direct-complete ");
> goto Complete;
> }
>
> - pm_runtime_enable(dev);
> + pm_runtime_relinquish(dev);
> }
> dev->power.direct_complete = false;
> }
>
>
>
Kind regards
Uffe
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