[PATCH V2 03/12] PM / Domains: Add on-off notifiers

[Rickard Andersson]

On 03/31/2013 12:17 AM, Rafael J. Wysocki wrote:
> On Thursday, March 28, 2013 05:11:29 PM Rickard Andersson wrote:
>> Some drivers needs to restore their context directly
>> when a power domain is activated. For example a driver
>> handling system bus settings must be able to restore
>> context before the bus is being used for the first time.
>> Other examples could be clock settings hardware blocks and
>> special debugging hardware blocks which should be restored
>> as early as possible in order to be able to debug direcly
>> from waking up. Typically these notifers are needed in
>> systems with CPU coupled power domains. The notifiers
>> are intended to be trigged by cpuidle driver or the
>> suspend ops hooks.
>>
>> The drivers that needs to use these notifiers are
>> some special cases. Most drivers should not use this
>> method and instead control their context via the
>> pm_runtime interface.
>>
>> Signed-off-by: Rickard Andersson<rickard.andersson at stericsson.com>
>> ---
>> I believe notifiers are the best solution to the problem of
>> restoring context early when waking up after sleep.
> I don't.

Some motivation would be good.
>> It is similar to what is done in /kernel/cpu_pm.c
> Which is causing tons of problems to happen.

What type of problems have you seen with the notifiers in 
"/kernel/cpu_pm.c"?
>> but but for a generic power domain instead.
> Which has a potential of being even worse.
>
>> An alternative solution could be to try to call the drivers
>> runtime_resume/runtime_suspend callbacks instead via genpd
>> from cpuidle or suspend/resume. I do not recommend that
>> solution for the following reasons:
>>
>> * Altered use of runtime PM. As it is today the driver itself
>>    controls when to runtime-suspend/runtime-resume.
> That's not correct.
>
>> * Runtime PM is disabled during late stages of suspend.
>> * Complicates runtime PM for a few special cases.
> Well, quite frankly, it is hard to say what problem this is supposed to
> address from your description.  Care to give some more details?
>
> Rafael
The problem is that some hardware blocks needs to be restored as early 
as possible after leaving the U8500 CPU coupled sleep state ApSleep (APE 
power domain being off). This is comparable to CPU needing early restore 
using "/kernel/cpu_pm.c" but for the APE power domain instead.
One could argue that one should save/restore the context directly in the 
cpuidle driver instead but that means duplicated code since hardware 
block registers will be modified both in the block driver and in the 
cpuidle driver. With the notifiers solution the cpuidle driver does not 
need to be aware of which hardware blocks that is being included in the 
APE power domain (needing early context restore), it is the same for 
system suspend/resume. Cpuidle and system suspend/resume should use the 
function pm_genpd_notify_power_on_off(..) to tell the system that it 
will change/has changed the state of a certain power domain.
Note that only a few of the hardware blocks in the APE power domain 
needs to use these notifiers, most drivers will do fine using pm_runtime.

If you for example look at patch "[PATCH V2 06/12] clk: ux500: Add PRCC 
power management" you can see that all PRCC clock registers are handled 
in the clock driver. There is no need to put duplicated code handling 
clocks context in "/arch/arm/mach-ux500/" for suspend/resume and 
cpuidle. Clock settings should be set directly as soon as possible after 
leaving the sleep state ApSleep, that is why the notifiers are being used.

If you do not think this mechanism is a way forward then please advice 
how you think is should be solved.

Thanks
Rickard
>
>> ---
>>   drivers/base/power/domain.c | 63 +++++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/pm_domain.h   | 22 ++++++++++++++++
>>   2 files changed, 85 insertions(+)
>>
>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>> index acc3a8d..91e3b7d 100644
>> --- a/drivers/base/power/domain.c
>> +++ b/drivers/base/power/domain.c
>> @@ -1956,6 +1956,68 @@ int pm_genpd_name_detach_cpuidle(const char *name)
>>   	return pm_genpd_detach_cpuidle(pm_genpd_lookup_name(name));
>>   }
>>
>> +/**
>> + * pm_genpd_register_on_off_notifier - Register to early power on /
>> + * late power off notifications.
>> + * Only use this function if absolutly needed. It is only intended to be
>> + * used for power domains that are coupled with the CPU, that is, power
>> + * domains being controlled from cpuidle and the platform suspend ops hooks.
>> + * Also only devices that needs their context to be restored directly when
>> + * leaving a sleep state should use this method. Most devices should be
>> + * fine handling their context and power domains via pm_runtime.
>> + * @dev: Device to register.
>> + * @nb: Notifier block to be registered.
>> + */
>> +int pm_genpd_register_on_off_notifier(struct device *dev,
>> +				      struct notifier_block *nb)
>> +{
>> +	struct generic_pm_domain *genpd;
>> +
>> +	dev_dbg(dev, "%s()\n", __func__);
>> +
>> +	genpd = dev_to_genpd(dev);
>> +
>> +	return atomic_notifier_chain_register(&genpd->on_off_notifier, nb);
>> +}
>> +
>> +/**
>> + * pm_genpd_unregister_on_off_notifier - Unregister to early power on /
>> + * late power off notification.
>> + * @dev: Device to unregister.
>> + * @nb: Notifier block to be unregistered.
>> + */
>> +int pm_genpd_unregister_on_off_notifier(struct device *dev,
>> +					struct notifier_block *nb)
>> +{
>> +	struct generic_pm_domain *genpd;
>> +
>> +	dev_dbg(dev, "%s()\n", __func__);
>> +
>> +	genpd = dev_to_genpd(dev);
>> +
>> +	return atomic_notifier_chain_unregister(&genpd->on_off_notifier, nb);
>> +}
>> +
>> +/**
>> + * pm_genpd_notify_power_on_off - Notify that the CPU coupled power
>> + * domain is going to be powered off or has been powered on.5D
>> + * Intended users of this function are cpuidle drivers and the platform
>> + * suspend operations implementation.
>> + * @genpd: pm domain that will change state.
>> + * @power_on_off: true = has been powered on, false = will power off.
>> + */
>> +int pm_genpd_notify_power_on_off(struct generic_pm_domain *genpd,
>> +				 bool power_on_off)
>> +{
>> +	if (IS_ERR_OR_NULL(genpd))
>> +		return -EINVAL;
>> +
>> +	atomic_notifier_call_chain((&genpd->on_off_notifier),
>> +				   power_on_off, NULL);
>> +
>> +	return 0;
>> +}
>> +
>>   /* Default device callbacks for generic PM domains. */
>>
>>   /**
>> @@ -2137,6 +2199,7 @@ void pm_genpd_init(struct generic_pm_domain *genpd,
>>   	atomic_set(&genpd->sd_count, 0);
>>   	genpd->status = is_off ? GPD_STATE_POWER_OFF : GPD_STATE_ACTIVE;
>>   	init_waitqueue_head(&genpd->status_wait_queue);
>> +	ATOMIC_INIT_NOTIFIER_HEAD(&genpd->on_off_notifier);
>>   	genpd->poweroff_task = NULL;
>>   	genpd->resume_count = 0;
>>   	genpd->device_count = 0;
>> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
>> index 7c1d252..bf5e7d514 100644
>> --- a/include/linux/pm_domain.h
>> +++ b/include/linux/pm_domain.h
>> @@ -82,6 +82,7 @@ struct generic_pm_domain {
>>   	bool cached_power_down_ok;
>>   	struct device_node *of_node; /* Node in device tree */
>>   	struct gpd_cpu_data *cpu_data;
>> +	struct atomic_notifier_head on_off_notifier;
>>   };
>>
>>   static inline struct generic_pm_domain *pd_to_genpd(struct dev_pm_domain *pd)
>> @@ -159,6 +160,12 @@ extern int pm_genpd_attach_cpuidle(struct generic_pm_domain *genpd, int state);
>>   extern int pm_genpd_name_attach_cpuidle(const char *name, int state);
>>   extern int pm_genpd_detach_cpuidle(struct generic_pm_domain *genpd);
>>   extern int pm_genpd_name_detach_cpuidle(const char *name);
>> +extern int pm_genpd_register_on_off_notifier(struct device *dev,
>> +					     struct notifier_block *nb);
>> +extern int pm_genpd_unregister_on_off_notifier(struct device *dev,
>> +					struct notifier_block *nb);
>> +extern int pm_genpd_notify_power_on_off(struct generic_pm_domain *genpd,
>> +				  bool power_on_off);
>>   extern void pm_genpd_init(struct generic_pm_domain *genpd,
>>   			  struct dev_power_governor *gov, bool is_off);
>>
>> @@ -243,6 +250,21 @@ static inline int pm_genpd_name_detach_cpuidle(const char *name)
>>   {
>>   	return -ENOSYS;
>>   }
>> +static inline int pm_genpd_register_on_off_notifier(struct device *dev,
>> +						    struct notifier_block *nb)
>> +{
>> +	return -ENOSYS;
>> +}
>> +static inline int pm_genpd_unregister_on_off_notifier(struct device *dev,
>> +						      struct notifier_block *nb)
>> +{
>> +	return -ENOSYS;
>> +}
>> +static inline int pm_genpd_notify_power_on_off(struct generic_pm_domain *genpd,
>> +					       bool power_on_off)
>> +{
>> +	return -ENOSYS;
>> +}
>>   static inline void pm_genpd_init(struct generic_pm_domain *genpd,
>>   				 struct dev_power_governor *gov, bool is_off)
>>   {
>>