[REPORT_ISSUE]: RK3399 pd power down failed

[Ulf Hansson]

On Tue, 23 Feb 2021 at 18:09, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
>
> On Tuesday, February 23, 2021 12:30:39 PM CET Ulf Hansson wrote:
> > On Wed, 20 Jan 2021 at 10:30, zhangqing at rock-chips.com
> > <zhangqing at rock-chips.com> wrote:
> > >
> > > Hi, Heiko :
> > >
> > > In rk3399 evb board,  I found a probabilistic problem about PD. Turning off PD occasionally failed.
> > >
> > > log show：
> > > Open the vop
> > > #modetest -M rockchip -s 42 at 36:1536x2048 -P 31 at 36:1536x2048 at AR24 -a
> > >
> > > close the vop
> > > #enter
> > >
> > >  # cat sys/kernel/debug/pm_genpd/pm_genpd_summary
> > > domain                          status          slaves
> > >     /device                                             runtime status
> > > ----------------------------------------------------------------------
> > > pd_vopl                         off
> > > pd_vopb                         on
> > >     /devices/platform/ff903f00.iommu                     suspended
> > >     /devices/platform/ff900000.vop                          suspended
> > >
> > > I have checked the codes and concluded that there is a window of time for PD to be closed when using the device link. Once queue_work is executed immediately,  PD power off may be failed.
> > > The process is as follows:
> > >
> > > VOP requests to power off PD:
> > > pm_runtime_put_sync(vop->dev)
> > >     -> rpm_idle(vop)
> > >         -> rpm_suspend(vop)
> > >             -> __update_runtime_status(dev, RPM_SUSPENDING)
> > >                 -> rpm_callback(vop)
> > >                     -> __rpm_callback(vop)
> > >                         -> do power off pd callback(genpd_power_off)
> > >                             -> list_for_each_entry(pdd, &genpd->dev_list, list_node), ff900000.vop: suspending， ff903f00.iommu : active，so not_suspended = 2 return -EBUSY; Not really power off PD。
> > >                                 -> Handle link device callbacks according to device link（rpm_put_suppliers）
> > >                                     -> pm_runtime_put(link->supplier)
> > >                                         -> queue_work(pm_wq, &dev->power.work), execute immediately
> > >                                             ->rpm_idle(iommu)
> > >                                                 -> rpm_suspend(iommu)
> > >                                                     -> rpm_callback(iommu)
> > >                                                         -> rk_iommu_suspend
> > >                                                             ->  do power off pd callback(genpd_power_off)
> > >                                                                 -> list_for_each_entry(pdd, &genpd->dev_list, list_node), ff900000.vop: suspending， ff903f00.iommu : suspending，so not_suspended = 2 return -EBUSY; Not really power off PD。
> > >                                                                     -> iommu do __update_runtime_status(dev, RPM_SUSPENDED)
> > >                                                                         -> vop do __update_runtime_status(dev, RPM_SUSPENDED)
> >
> > So, rpm_suspend() tries to suspend the supplier device link via
> > rpm_put_suppliers(), before it has updated its consumer device's state
> > to RPM_SUSPENDED.
> >
> > This looks worrying to me, both because it's seems wrong to allow a
> > supplier to be suspended before a consumers device's state has reached
> > RPM_SUSPENDED - but also because it's not consistent with the way we
> > treat parent/child devices. The child's state will always be set to
> > RPM_SUSPENDED, before we try to suspend its parent by calling
> > rpm_idle() for it in rpm_suspend().
> >
> > Rafael, what's your take on this? Would it make sense to align the
> > behavior for consumer/supplier-links in rpm_suspend() according to
> > child/parents?
>
> Suspending the suppliers before changing the consumer RPM status to
> "suspended" is indeed incorrect, which is something I overlooked when
> writing the code in question.
>
> Fortunately, it seems to be relatively easy to address.
>
> Please see the appended tentative patch (untested).  It also avoids reading
> runtime_status outside the lock which is arguably fishy.

Great, thanks for your quick reply!

A minor comment on the below change, but otherwise feel free add my
reviewed-by tag.

Kind regards
Uffe

>
> ---
>  drivers/base/power/runtime.c |   24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
>
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -330,7 +330,11 @@ static int __rpm_callback(int (*cb)(stru
>
>         if (dev->power.irq_safe) {
>                 spin_unlock(&dev->power.lock);
> +       } else if (!use_links) {
> +               spin_unlock_irq(&dev->power.lock);
>         } else {
> +               bool get = dev->power.runtime_status == RPM_RESUMING;
> +
>                 spin_unlock_irq(&dev->power.lock);
>
>                 /*
> @@ -340,7 +344,7 @@ static int __rpm_callback(int (*cb)(stru
>                  * routine returns, so it is safe to read the status outside of
>                  * the lock.
>                  */
> -               if (use_links && dev->power.runtime_status == RPM_RESUMING) {
> +               if (get) {
>                         idx = device_links_read_lock();
>
>                         retval = rpm_get_suppliers(dev);
> @@ -355,7 +359,21 @@ static int __rpm_callback(int (*cb)(stru
>
>         if (dev->power.irq_safe) {
>                 spin_lock(&dev->power.lock);
> +       } if (!use_links) {

This should be an "else if", I think.

> +               spin_lock_irq(&dev->power.lock);
>         } else {
> +               bool put;
> +
> +               spin_lock_irq(&dev->power.lock);
> +
> +               put = dev->power.runtime_status == RPM_SUSPENDING && !retval;
> +               if (put)
> +                       __update_runtime_status(dev, RPM_SUSPENDED);
> +               else
> +                       put = dev->power.runtime_status == RPM_RESUMING && retval;
> +
> +               spin_unlock_irq(&dev->power.lock);
> +
>                 /*
>                  * If the device is suspending and the callback has returned
>                  * success, drop the usage counters of the suppliers that have
> @@ -363,9 +381,7 @@ static int __rpm_callback(int (*cb)(stru
>                  *
>                  * Do that if resume fails too.
>                  */
> -               if (use_links
> -                   && ((dev->power.runtime_status == RPM_SUSPENDING && !retval)
> -                   || (dev->power.runtime_status == RPM_RESUMING && retval))) {
> +               if (put) {
>                         idx = device_links_read_lock();
>
>   fail:
>
>
>