Subject: [PATCH RFC 2/3] PM / Domains: Support atomic PM domains

From: [email-masked] (Krzysztof Kozlowski)
Date: Sun, 07 Jun 2015 18:21:04 +0900

W dniu 05.06.2015 o 07:29, Lina Iyer pisze:
> Power Domains currently support turning on/off only in process context.
> This restricts the usage of PM domains to devices and domains that
> could be powered on/off in irq disabled contexts as the mutexes used in
> GenPD allows for cpu sleep while waiting for locks.

I can find also other use case: currently the power domain with irq_safe
devices is always powered on. With the patch it could be powered off (of
course if the driver/mach code is irq-safe).

> 
> Genpd inherently provides support for devices, domain hierarchy and can
> be used to represent cpu clusters like in ARM's big.Little, where, each
> cpu cluster is in its domain, with supporting caches and other
> peripheral hardware. Multiple such domains could be part of another
> domain. Because mutexes are used to protect and synchronize domain
> operations and cpu idle operations are inherently atomic, the use of
> genpd is not possible for runtime suspend and resume of the pm domain.
> Replacing the locks to spinlocks would allow cpu domain to be be powered
> off to save power, when all the cpus are powered off.
> 
> However, not all domains can operate in irq-safe contexts and usually
> would need to sleep during domain operations. So genpd has to support
> both the cases, where the domain is or is not irq-safe. The irq-safe
> attribute is therefore domain specific.
> 
> To achieve domain specific locking, set the GENPD_FLAG_IRQ_SAFE flag
> while defining the domain. This determines if the domain should use a
> spinlock instead of a mutex. Locking is abstracted through
> genpd_lock_domain() and genpd_unlock_domain() functions that use the
> flag to determine the locking to be used for this domain.
> 
> The restriction this imposes on the domain hierarchy is that subdomains
> and all devices in the hierarchy also be irq-safe. Non irq-safe domains
> may continue to have irq-safe devices, but not the other way around.

So an irq-safe device can be put in irq-safe subdomain which can be a
child of non-irq-safe topdomain?

> 
> Cc: Ulf Hansson <[email-masked]>
> Cc: Rafael J. Wysocki <[email-masked]>
> Cc: Kevin Hilman <[email-masked]>
> Signed-off-by: Lina Iyer <[email-masked]>
> ---
>  drivers/base/power/domain.c | 200 ++++++++++++++++++++++++++++++++++----------
>  include/linux/pm_domain.h   |  11 ++-

Documentation should also be reflected.

>  2 files changed, 164 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index dfd7595..8b89d15 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -50,6 +50,71 @@
>  static LIST_HEAD(gpd_list);
>  static DEFINE_MUTEX(gpd_list_lock);
>  
> +static inline int genpd_lock_domain_noirq(struct generic_pm_domain *genpd,
> +					unsigned int subclass)
> +	__acquires(&genpd->slock)
> +{
> +	unsigned long flags;
> +
> +	if (unlikely(subclass > 0))
> +		spin_lock_irqsave_nested(&genpd->slock, flags, subclass);
> +	else
> +		spin_lock_irqsave(&genpd->slock, flags);
> +
> +	genpd->flags = flags;
> +
> +	return 0;
> +}
> +
> +static inline int genpd_unlock_domain_noirq(struct generic_pm_domain *genpd)
> +	__releases(&genpd->slock)
> +{
> +	spin_unlock_irqrestore(&genpd->slock, genpd->lock_flags);
> +	return 0;
> +}
> +
> +static inline int genpd_lock_domain_irq(struct generic_pm_domain *genpd,
> +					unsigned int subclass)
> +	__acquires(&genpd->mlock)
> +{
> +	if (unlikely(subclass > 0))
> +		mutex_lock_nested(&genpd->mlock, subclass);
> +	else
> +		mutex_lock(&genpd->mlock);
> +
> +	return 0;
> +}
> +
> +static inline int genpd_lock_domain_interruptible_irq(
> +				struct generic_pm_domain *genpd)
> +	__acquires(&genpd->mlock)
> +{
> +	return mutex_lock_interruptible(&genpd->mlock);
> +}
> +
> +static inline int genpd_unlock_domain_irq(struct generic_pm_domain *genpd)
> +	__releases(&genpd->mlock)
> +{
> +	mutex_unlock(&genpd->mlock);
> +	return 0;
> +}
> +
> +#define genpd_lock_domain(genpd)				\
> +	(genpd->irq_safe ? genpd_lock_domain_noirq(genpd, 0)	\
> +			: genpd_lock_domain_irq(genpd, 0))
> +
> +#define genpd_lock_domain_nested(genpd)				\
> +	(genpd->irq_safe ? genpd_lock_domain_noirq(genpd, SINGLE_DEPTH_NESTING)\
> +			: genpd_lock_domain_irq(genpd, SINGLE_DEPTH_NESTING))
> +
> +#define genpd_unlock_domain(genpd)				\
> +	(genpd->irq_safe ? genpd_unlock_domain_noirq(genpd)	\
> +			: genpd_unlock_domain_irq(genpd))
> +
> +#define genpd_lock_domain_interruptible(genpd)			\
> +	(genpd->irq_safe ? genpd_lock_domain_noirq(genpd, 0)	\
> +			: genpd_lock_domain_interruptible_irq(genpd))

Why macros? You are not using here benefits of a macro and they are
called just like ordinary functions.

You added "domain" prefix but genpd already contains this. genod_lock(),
genpd_lock_nested() etc. should be sufficient, unless there is a
conflict, similar name planned or you plan to lock something else
(genpd_lock_device?).

> +
>  static struct generic_pm_domain *pm_genpd_lookup_name(const char *domain_name)
>  {
>  	struct generic_pm_domain *genpd = NULL, *gpd;
> @@ -262,9 +327,9 @@ int pm_genpd_poweron(struct generic_pm_domain *genpd)
>  {
>  	int ret;
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock_domain(genpd);
>  	ret = __pm_genpd_poweron(genpd);
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock_domain(genpd);
>  	return ret;
>  }
>  
> @@ -326,9 +391,9 @@ static int genpd_dev_pm_qos_notifier(struct notifier_block *nb,
>  		spin_unlock_irq(&dev->power.lock);
>  
>  		if (!IS_ERR(genpd)) {
> -			mutex_lock(&genpd->lock);
> +			genpd_lock_domain(genpd);
>  			genpd->max_off_time_changed = true;
> -			mutex_unlock(&genpd->lock);
> +			genpd_unlock_domain(genpd);
>  		}
>  
>  		dev = dev->parent;
> @@ -387,7 +452,7 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
>  			return -EBUSY;
>  
>  		if (pdd->dev->driver && (!pm_runtime_suspended(pdd->dev)
> -		    || pdd->dev->power.irq_safe))
> +			|| (pdd->dev->power.irq_safe && !genpd->irq_safe)))
>  			not_suspended++;
>  	}
>  
> @@ -453,9 +518,9 @@ static void genpd_power_off_work_fn(struct work_struct *work)
>  
>  	genpd = container_of(work, struct generic_pm_domain, power_off_work);
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock_domain(genpd);
>  	pm_genpd_poweroff(genpd);

Ipm_genpd_poweroff() calls __pm_genpd_save_device() which grabs mutex.
At least in next-20150604 but maybe the patches, which this depends on,
changed it?

> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock_domain(genpd);
>  }
>  
>  /**
> @@ -478,12 +543,8 @@ static int pm_genpd_runtime_suspend(struct device *dev)
>  	if (IS_ERR(genpd))
>  		return -EINVAL;
>  
> -	/*
> -	 * We can't allow to power off the PM domain if it holds an irq_safe
> -	 * device. That's beacuse we use mutexes to protect data while power
> -	 * off and on the PM domain, thus we can't execute in atomic context.
> -	 */
> -	if (dev->power.irq_safe)
> +	/* We can't allow to power off a domain that is also not irq safe. */
> +	if (dev->power.irq_safe && !genpd->irq_safe)
>  		return -EBUSY;
>  
>  	stop_ok = genpd->gov ? genpd->gov->stop_ok : NULL;
> @@ -500,11 +561,19 @@ static int pm_genpd_runtime_suspend(struct device *dev)
>  		return ret;
>  	}
>  
> -	mutex_lock(&genpd->lock);
> +	/*
> +	 * If power.irq_safe is set, this routine will be run with interrupts
> +	 * off, so suspend only if the power domain is irq_safe.
> +	 */
> +	if (dev->power.irq_safe && !genpd->irq_safe)
> +		return 0;
> +
> +	genpd_lock_domain(genpd);
> +
>  	genpd->in_progress++;
>  	pm_genpd_poweroff(genpd);
>  	genpd->in_progress--;
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock_domain(genpd);
>  
>  	return 0;
>  }
> @@ -528,13 +597,16 @@ static int pm_genpd_runtime_resume(struct device *dev)
>  	if (IS_ERR(genpd))
>  		return -EINVAL;
>  
> -	/* If power.irq_safe, the PM domain is never powered off. */
> -	if (dev->power.irq_safe)
> +	/*
> +	 * If power.irq_safe and domain is not, then
> +	 * the PM domain is never powered off.
> +	 */
> +	if (dev->power.irq_safe && !genpd->irq_safe)
>  		return genpd_start_dev_no_timing(genpd, dev);
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock_domain(genpd);
>  	ret = __pm_genpd_poweron(genpd);
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock_domain(genpd);
>  
>  	if (ret)
>  		return ret;
> @@ -729,14 +801,14 @@ static int pm_genpd_prepare(struct device *dev)
>  	if (resume_needed(dev, genpd))
>  		pm_runtime_resume(dev);
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock_domain(genpd);
>  
>  	if (genpd->prepared_count++ == 0) {
>  		genpd->suspended_count = 0;
>  		genpd->suspend_power_off = genpd->status == GPD_STATE_POWER_OFF;
>  	}
>  
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock_domain(genpd);
>  
>  	if (genpd->suspend_power_off) {
>  		pm_runtime_put_noidle(dev);
> @@ -754,12 +826,12 @@ static int pm_genpd_prepare(struct device *dev)
>  
>  	ret = pm_generic_prepare(dev);
>  	if (ret) {
> -		mutex_lock(&genpd->lock);
> +		genpd_lock_domain(genpd);
>  
>  		if (--genpd->prepared_count == 0)
>  			genpd->suspend_power_off = false;
>  
> -		mutex_unlock(&genpd->lock);
> +		genpd_unlock_domain(genpd);
>  		pm_runtime_enable(dev);
>  	}
>  
> @@ -1116,13 +1188,13 @@ static void pm_genpd_complete(struct device *dev)
>  	if (IS_ERR(genpd))
>  		return;
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock_domain(genpd);
>  
>  	run_complete = !genpd->suspend_power_off;
>  	if (--genpd->prepared_count == 0)
>  		genpd->suspend_power_off = false;
>  
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock_domain(genpd);
>  
>  	if (run_complete) {
>  		pm_generic_complete(dev);
> @@ -1266,11 +1338,18 @@ int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
>  	if (IS_ERR_OR_NULL(genpd) || IS_ERR_OR_NULL(dev))
>  		return -EINVAL;
>  
> +	/* Devices in an IRQ safe PM Domain have to be irq safe too */

Why? Can you add this information here? Previously there was a reason in
case of irq_safe devices which you removed leaving only policy.

Best regards,
Krzysztof