Hi,
On 24-03-18 15:19, Lukas Wunner wrote:
On Sat, Mar 24, 2018 at 12:07:10PM +0100, Hans de Goede wrote:
On 24-03-18 09:02, Lukas Wunner wrote:
On Mon, Mar 19, 2018 at 10:02:36PM +0100, Hans de Goede wrote:
The pm_runtime_set_suspended() call in bcm_close() is intended as a
counterpart to the pm_runtime_set_active() call from bcm_request_irq()
(which gets called from bcm_setup()).
The pm_runtime_set_active() call only happens if our pre-requisites for
doing runtime-pm are met. This commit adds the same check to the
pm_runtime_set_suspended() call to avoid the runtime-pm state getting
stuck in suspended after after a bcm_close().
Have you actually observed the state getting stuck in suspended?
I'm asking because I don't quite see how this could happen:
pm_runtime_set_suspended() becomes a no-op unless runtime PM is disabled.
Now, a few lines further up in bcm_close(), pm_runtime_disable() is only
called under the conditions you're adding here. If it's not called,
pm_runtime_set_suspended() doesn't have any effect anyway so adding the
conditions is pointless. Am I missing something?
All devices start with runtime-pm disabled and on devices without
an IRQ we never enable it. So when the pm_runtime_set_suspended()
gets called runtime-pm is still in its initial disabled state.
Okay but the device's initial state is set to RPM_SUSPENDED by
pm_runtime_init() and AFAICS neither the platform nor acpi buses
subsequently set it to RPM_ACTIVE, so the device is in suspended
state anyway, unless I've overlooked some detail.
Ah, no you're right, I assumed that devices would default to
RPM_ACTIVE (which corresponds to value 0), but you are right
they are set to suspended by default.
So this patch can be dropped.
Marcel: It would still be nice to get the second patch from
this series merged.
Which raises another question, bcm_suspend() only calls
bcm_suspend_device() if it's runtime active. So devices
without IRQ, which are always in runtime suspended state,
are apparently never orderly put to sleep on ->suspend.
No that is not a problem, pm_runtime_active() is defined as:
static inline bool pm_runtime_active(struct device *dev)
{
return dev->power.runtime_status == RPM_ACTIVE
|| dev->power.disable_depth;
}
On devices without an IRQ we never enable runtime_pm, so
dev->power.disable_depth stays at its initial value of 1 and
this function will return 1.
Also, if the device is always in suspended state, there's nothing
that keeps the UART in active state. Has anyone ever actually
tested if this driver works without IRQ?
AFAIK the code deciding to suspend parents also uses
pm_runtime_active()
The reason why I was worried about the suspended status field is
because there also is pm_runtime_status_suspended() which only
checks the status field, but I guess that is only used in
special cases.
Related: I notice that bcm_resume() calls pm_runtime_set_active().
Doesn't that have the effect that if the device is not opened and
the system goes to sleep, the device is kept in runtime active state
after resume and thus prevents the UART from runtime suspending until
the device is opened?
AFAIK this just tells runtime pm that we've woken up the device
(which we have), so that it does not call bcm_resume_device() *again*
on the first runtime_pm_get().
That's odd, by default the PM core runtime resumes a device before
going to system sleep, the only exception is if the devices uses
the "direct_complete" procedure, which requires that ->prepare
returns a positive int. The platform bus doesn't even have a
->prepare hook, so never uses direct complete AFAICS, and the acpi
bus uses direct_complete only under certain conditions and even then
devices seem to be resumed to runtime active state when the system wakes,
according to the code comment in acpi_subsys_resume_noirq().
So the pm_runtime_set_active() in bcm_resume() looks odd to me.
This code precedes my involvement in the driver, I agree this looks
a bit weird.
The pm_runtime_enable() will start the
autosuspend timer I believe (I could be wrong I'm not an expert on this)
and then we will autosuspend again after the timer expires.
No, pm_runtime_enable() doesn't do that, but device_complete calls
pm_runtime_put() as the last step when coming out of system sleep,
and that will start the autosuspend timer.
Ok.
Regards,
Hans
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
