On Tue, Oct 24, 2017 at 10:49 AM, Rafael J. Wysocki <r...@rjwysocki.net> wrote:
> On Tuesday, October 24, 2017 7:54:09 AM CEST Ramesh Thomas wrote:
>> On 2017-10-20 at 13:27:34 +0200, Rafael J. Wysocki wrote:
>> > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
>> >
[cut]
>> > @@ -63,10 +60,14 @@ static bool default_suspend_ok(struct de
>> >
>> > spin_unlock_irqrestore(&dev->power.lock, flags);
>> >
>> > - if (constraint_ns < 0)
>> > + if (constraint_ns == 0)
>> > return false;
>> >
>> > - constraint_ns *= NSEC_PER_USEC;
>> > + if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
>> > + constraint_ns = -1;
>> > + else
>> > + constraint_ns *= NSEC_PER_USEC;
>> > +
>> > /*
>> > * We can walk the children without any additional locking, because
>> > * they all have been suspended at this point and their
>> > @@ -76,14 +77,19 @@ static bool default_suspend_ok(struct de
>> > device_for_each_child(dev, &constraint_ns,
>> > dev_update_qos_constraint);
>> >
>> > - if (constraint_ns > 0) {
>> > - constraint_ns -= td->suspend_latency_ns +
>> > - td->resume_latency_ns;
>> > - if (constraint_ns == 0)
>> > - return false;
>> > + if (constraint_ns < 0) {
>> > + /* The children have no constraints. */
>> > + td->effective_constraint_ns =
>> > PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
>> > + td->cached_suspend_ok = true;
>> > + } else {
>> > + constraint_ns -= td->suspend_latency_ns +
>> > td->resume_latency_ns;
>> > + if (constraint_ns > 0) {
>> > + td->effective_constraint_ns = constraint_ns;
>> > + td->cached_suspend_ok = true;
>> > + } else {
>> > + td->effective_constraint_ns = 0;
>>
>> Previously effective_constraint_ns was left as -1 if constraint_ns becomes 0
>> Not sure if this change is intentional.
>
> Yes, it is.
>
>> I think at dev_update_qos_constraint, this can cause to skip call to
>> dev_pm_qos_read_value.
>
> I need to double check that.
If constraint_ns becomes 0 (or less) here, power cannot be removed
from the device, because it would add an unacceptable latency.
Thus effective_constraint_ns has to be 0 for it to indicate that
situation. If it was left at -1, it would mean "no requirement", but
that wouldn't be correct.
Thanks,
Rafael
