Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 11 Feb 2019 23:41:43 +0100 | Subject | Re: [PATCH 1/2] PM-runtime: Take suppliers into account in __pm_runtime_set_status() |
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On Mon, Feb 11, 2019 at 2:28 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > On Thu, 7 Feb 2019 at 19:46, Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > > > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > If the target device has any suppliers, as reflected by device links > > to them, __pm_runtime_set_status() does not take them into account, > > which is not consistent with the other parts of the PM-runtime > > framework and may lead to programming mistakes. > > > > Modify __pm_runtime_set_status() to take suppliers into account by > > activating them upfront if the new status is RPM_ACTIVE and > > deactivating them on exit if the new status is RPM_SUSPENDED. > > > > If the activation of one of the suppliers fails, the new status > > will be RPM_SUSPENDED and the (remaining) suppliers will be > > deactivated on exit (the child count of the device's parent > > will be dropped too then). > > > > Of course, adding device links locking to __pm_runtime_set_status() > > means that it cannot be run fron interrupt context, so make it use > > spin_lock_irq() and spin_unlock_irq() instead of spin_lock_irqsave() > > and spin_unlock_irqrestore(), respectively. > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > Rafael, thanks for working on this! > > I am running some tests at my side, but still not achieving the > behavior I expect to. Will let you know when I have more details, but > first some comments below. > > > --- > > drivers/base/power/runtime.c | 45 ++++++++++++++++++++++++++++++++++++++----- > > 1 file changed, 40 insertions(+), 5 deletions(-) > > > > Index: linux-pm/drivers/base/power/runtime.c > > =================================================================== > > --- linux-pm.orig/drivers/base/power/runtime.c > > +++ linux-pm/drivers/base/power/runtime.c > > @@ -1102,20 +1102,43 @@ EXPORT_SYMBOL_GPL(pm_runtime_get_if_in_u > > * and the device parent's counter of unsuspended children is modified to > > * reflect the new status. If the new status is RPM_SUSPENDED, an idle > > * notification request for the parent is submitted. > > + * > > + * If @dev has any suppliers (as reflected by device links to them), and @status > > + * is RPM_ACTIVE, they will be activated upfront and if the activation of one > > + * of them fails, the status of @dev will be changed to RPM_SUSPENDED (instead > > + * of the @status value) and the suppliers will be deacticated on exit. The > > + * error returned by the failing supplier activation will be returned in that > > + * case. > > */ > > int __pm_runtime_set_status(struct device *dev, unsigned int status) > > { > > struct device *parent = dev->parent; > > - unsigned long flags; > > bool notify_parent = false; > > int error = 0; > > > > if (status != RPM_ACTIVE && status != RPM_SUSPENDED) > > return -EINVAL; > > > > - spin_lock_irqsave(&dev->power.lock, flags); > > + /* > > + * If the new status is RPM_ACTIVE, the suppliers can be activated > > + * upfront regardless of the current status, because next time > > + * rpm_put_suppliers() runs, the rpm_active refcounts of the links > > + * involved will be dropped down to one anyway. > > + */ > > + if (status == RPM_ACTIVE) { > > + int idx = device_links_read_lock(); > > + > > + error = rpm_get_suppliers(dev); > > + if (error) > > + status = RPM_SUSPENDED; > > + > > + device_links_read_unlock(idx); > > + } > > This doesn't look right to me, and more importantly, this isn't > consistent with how we treat a parent/child.
It cannot be entirely consistent with that, because you cannot walk the suppliers under the device's power.lock.
The idea here is that activating suppliers upfront if the new status is RPM_ACTIVE shouldn't hurt regardless.
> More precisely, I think you need to check "if > (!dev->power.runtime_error && !dev->power.disable_depth)" and also > whether "dev->power.runtime_status == status", before deciding to call > rpm_get_suppliers() above. Otherwise you may end up resuming suppliers > and/or increasing the link->rpm_active count, when you shouldn't.
Resuming suppliers unnecessarily is not particularly efficient, but it is not incorrect. Incrementing their rpm_active temporarily also isn't incorrect as long as the rpm_active values are correct on exit (and note that incementing them if the consumer's status is RPM_ACTIVE doesn't even matter).
> In other words, expecting __pm_runtime_set_status() to be called in > "balanced" manner isn't correct.
There is no such expectation here.
There is a possible race between __pm_runtime_set_status() and runtime suspend or resume of the device in case PM-runtime is enabled for it when __pm_runtime_set_status() is called, but it shouldn't occur if __pm_runtime_set_status() is used correctly (that is, when PM-runtime is disabled for the device).
I think I know how to avoid that race, though, so I'm going to post an incremental fix if that works out.
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