Messages in this thread Patch in this message | | | From | Ulf Hansson <> | Date | Tue, 30 Nov 2021 12:57:55 +0100 | Subject | Re: [PATCH] PM: runtime: Allow rpm_resume() to succeed when runtime PM is disabled |
| |
[...]
> > > > > > > > > > > > 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
| |