Re: [PATCH 3/9] PM / Domains: Support IRQ safe PM domains

[Kevin Hilman <khilman@kernel.org>]

Lina Iyer <lina.iyer@linaro.org> writes:

> Generic Power Domains currently support turning on/off only in process
> context. This prevents the usage of PM domains for domains that could be
> powered on/off in a context where IRQs are disabled. Many such domains
> exist today and do not get powered off, when the IRQ safe devices in
> that domain are powered off, because of this limitation.
>
> However, not all domains can operate in IRQ safe contexts. Genpd
> therefore, has to support both cases where the domain may or may not
> operate in IRQ safe contexts. Configuring genpd to use an appropriate
> lock for that domain, would allow domains that have IRQ safe devices to
> runtime suspend and resume, in atomic context.
>
> To achieve domain specific locking, set the domain's ->flag to
> GENPD_FLAG_IRQ_SAFE while defining the domain. This indicates that genpd
> should use a spinlock instead of a mutex for locking the domain. Locking
> is abstracted through genpd_lock() and genpd_unlock() functions that use
> the flag to determine the appropriate lock to be used for that domain.
> Domains that have lower latency to suspend and resume and can operate
> with IRQs disabled may now be able to save power, when the component
> devices and sub-domains are idle at runtime.
>
> The restriction this imposes on the domain hierarchy is that sub-domains
> and all devices in the IRQ safe domain's hierarchy also have to be IRQ
> safe, so that we dont try to lock a mutex, while holding a spinlock.
> Non-IRQ safe domains may continue to have devices and sub-domains that
> may or may not be IRQ safe.
>
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: Kevin Hilman <khilman@linaro.org>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Cc: Krzysztof Kozłowski <k.kozlowski@samsung.com>
> Signed-off-by: Lina Iyer <lina.iyer@linaro.org>

Approach seems good to me, some cosmetic issues below...

> ---
>  Documentation/power/devices.txt |  11 ++-
>  drivers/base/power/domain.c     | 201 +++++++++++++++++++++++++++++++---------
>  include/linux/pm_domain.h       |  11 ++-
>  3 files changed, 178 insertions(+), 45 deletions(-)
>
> diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
> index 8ba6625..6d8318c 100644
> --- a/Documentation/power/devices.txt
> +++ b/Documentation/power/devices.txt
> @@ -607,7 +607,16 @@ individually.  Instead, a set of devices sharing a power resource can be put
>  into a low-power state together at the same time by turning off the shared
>  power resource.  Of course, they also need to be put into the full-power state
>  together, by turning the shared power resource on.  A set of devices with this
> -property is often referred to as a power domain.
> +property is often referred to as a power domain. A power domain may also be
> +nested inside another power domain.
> +
> +Devices, by default, operate in process context and if a device can operate in
> +IRQ safe context, has to be explicitly set as IRQ safe. Power domains by
> +default, operate in process context but could have devices that are IRQ safe.
> +Such power domains cannot be powered on/off during runtime PM. On the other
> +hand, an IRQ safe PM domain that can be powered on/off and suspend or resumed
> +in an atomic context, may contain IRQ safe devices. Such domains may only
> +contain IRQ safe devices or IRQ safe sub-domains.
>  
>  Support for power domains is provided through the pm_domain field of struct
>  device.  This field is a pointer to an object of type struct dev_pm_domain,
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index ef8d19f..221feb0 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -53,6 +53,74 @@
>  static LIST_HEAD(gpd_list);
>  static DEFINE_MUTEX(gpd_list_lock);
>  
> +static inline int genpd_lock_noirq(struct generic_pm_domain *genpd,
> +					unsigned int subclass)

I don't like the _noirq naming, as in the context of suspend/resume,
that means no *device* IRQs, not no IRQs at all.  Maybe _atomic is
better, or _nosleep? or ...

> +	__acquires(&genpd->slock)
> +{
> +	unsigned long flags;
> +
> +	if (subclass > 0)
> +		spin_lock_irqsave_nested(&genpd->slock, flags, subclass);
> +	else
> +		spin_lock_irqsave(&genpd->slock, flags);
> +
> +	genpd->lock_flags = flags;
> +	return 0;
> +}
> +
> +static inline void genpd_unlock_noirq(struct generic_pm_domain *genpd)
> +	__releases(&genpd->slock)
> +{
> +	spin_unlock_irqrestore(&genpd->slock, genpd->lock_flags);
> +}
> +
> +static inline int genpd_lock_irq(struct generic_pm_domain *genpd,
> +					unsigned int subclass)
> +	__acquires(&genpd->mlock)
> +{
> +	if (subclass > 0)
> +		mutex_lock_nested(&genpd->mlock, subclass);
> +	else
> +		mutex_lock(&genpd->mlock);
> +	return 0;
> +}
> +
> +static inline int genpd_lock_interruptible_irq(struct generic_pm_domain *genpd)
> +	__acquires(&genpd->mlock)
> +{
> +	return mutex_lock_interruptible(&genpd->mlock);
> +}
> +
> +static inline void genpd_unlock_irq(struct generic_pm_domain *genpd)
> +	__releases(&genpd->mlock)
> +{
> +	mutex_unlock(&genpd->mlock);
> +}
> +
> +static inline int genpd_lock(struct generic_pm_domain *genpd)
> +{
> +	return genpd->irq_safe ? genpd_lock_noirq(genpd, 0)
> +			: genpd_lock_irq(genpd, 0);
> +}
> +
> +static inline int genpd_lock_nested(struct generic_pm_domain *genpd)
> +{
> +	return genpd->irq_safe ? genpd_lock_noirq(genpd, SINGLE_DEPTH_NESTING)
> +			: genpd_lock_irq(genpd, SINGLE_DEPTH_NESTING);
> +}
> +
> +static inline int genpd_lock_interruptible(struct generic_pm_domain *genpd)
> +{
> +	return genpd->irq_safe ? genpd_lock_noirq(genpd, 0)
> +			: genpd_lock_interruptible_irq(genpd);
> +}
> +
> +static inline void genpd_unlock(struct generic_pm_domain *genpd)
> +{
> +	return genpd->irq_safe ? genpd_unlock_noirq(genpd)
> +			: genpd_unlock_irq(genpd);
> +}
> +
>  static struct generic_pm_domain *pm_genpd_lookup_name(const char *domain_name)
>  {
>  	struct generic_pm_domain *genpd = NULL, *gpd;
> @@ -273,9 +341,9 @@ int pm_genpd_poweron(struct generic_pm_domain *genpd)
>  {
>  	int ret;
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock(genpd);
>  	ret = __pm_genpd_poweron(genpd);
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  	return ret;
>  }
>  
> @@ -335,9 +403,9 @@ 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(genpd);
>  			genpd->max_off_time_changed = true;
> -			mutex_unlock(&genpd->lock);
> +			genpd_unlock(genpd);
>  		}
>  
>  		dev = dev->parent;
> @@ -394,7 +462,13 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
>  		if (stat > PM_QOS_FLAGS_NONE)
>  			return -EBUSY;
>  
> -		if (!pm_runtime_suspended(pdd->dev) || pdd->dev->power.irq_safe)
> +		/*
> +		 * We do not want to power off the domain if the device is
> +		 * not suspended or an IRQ safe device is part of this
> +		 * non-IRQ safe domain.
> +		 */
> +		if (!pm_runtime_suspended(pdd->dev) ||
> +			(pdd->dev->power.irq_safe && !genpd->irq_safe))
>  			not_suspended++;

The !irq_safe check should maybe spit a warning via WARN_ONCE(), as this
would be useful in debugging domains that are not shutting down.

>  	}
>  
> @@ -460,9 +534,9 @@ 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(genpd);
>  	pm_genpd_poweroff(genpd);
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  }
>  
>  /**
> @@ -500,17 +574,19 @@ static int pm_genpd_runtime_suspend(struct device *dev)
>  	}
>  
>  	/*
> -	 * If power.irq_safe is set, this routine will be run with interrupts
> -	 * off, so it can't use mutexes.
> +	 * If power.irq_safe is set, this routine may be run with
> +	 * IRQ disabled, so suspend only if the power domain is
> +	 * irq_safe.
>  	 */
> -	if (dev->power.irq_safe)
> +	if (dev->power.irq_safe && !genpd->irq_safe)
>  		return 0;

Similarily, a WARN_ONCE() will probably be helpful here.

> -	mutex_lock(&genpd->lock);
> +	genpd_lock(genpd);
> +
>  	genpd->in_progress++;
>  	pm_genpd_poweroff(genpd);
>  	genpd->in_progress--;
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  
>  	return 0;
>  }
> @@ -535,15 +611,18 @@ 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) {
> +	/*
> +	 * As we dont power off a non IRQ safe domain, which holds
> +	 * an IRQ safe device, we dont need to restore power to it.
> +	 */
> +	if (dev->power.irq_safe && !genpd->irq_safe) {
>  		timed = false;
>  		goto out;
>  	}
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock(genpd);
>  	ret = __pm_genpd_poweron(genpd);
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  
>  	if (ret)
>  		return ret;
> @@ -743,14 +822,14 @@ static int pm_genpd_prepare(struct device *dev)
>  	if (resume_needed(dev, genpd))
>  		pm_runtime_resume(dev);
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock(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(genpd);
>  
>  	if (genpd->suspend_power_off) {
>  		pm_runtime_put_noidle(dev);
> @@ -768,12 +847,12 @@ static int pm_genpd_prepare(struct device *dev)
>  
>  	ret = pm_generic_prepare(dev);
>  	if (ret) {
> -		mutex_lock(&genpd->lock);
> +		genpd_lock(genpd);
>  
>  		if (--genpd->prepared_count == 0)
>  			genpd->suspend_power_off = false;
>  
> -		mutex_unlock(&genpd->lock);
> +		genpd_unlock(genpd);
>  		pm_runtime_enable(dev);
>  	}
>  
> @@ -1130,13 +1209,13 @@ static void pm_genpd_complete(struct device *dev)
>  	if (IS_ERR(genpd))
>  		return;
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock(genpd);
>  
>  	run_complete = !genpd->suspend_power_off;
>  	if (--genpd->prepared_count == 0)
>  		genpd->suspend_power_off = false;
>  
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  
>  	if (run_complete) {
>  		pm_generic_complete(dev);
> @@ -1280,11 +1359,17 @@ 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;
>  
> +	if (genpd->irq_safe && !dev->power.irq_safe) {
> +		dev_err(dev,
> +			"Devices in an IRQ safe domain have to be IRQ safe.\n");

This should also dump the PM domain, something like:

            dev_err(dev, "PM domain %s is IRQ safe; device has to be IRQ safe.\n")

> +		return -EINVAL;
> +	}
> +
>  	gpd_data = genpd_alloc_dev_data(dev, genpd, td);
>  	if (IS_ERR(gpd_data))
>  		return PTR_ERR(gpd_data);
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock(genpd);
>  
>  	if (genpd->prepared_count > 0) {
>  		ret = -EAGAIN;
> @@ -1301,7 +1386,7 @@ int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
>  	list_add_tail(&gpd_data->base.list_node, &genpd->dev_list);
>  
>   out:
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  
>  	if (ret)
>  		genpd_free_dev_data(dev, gpd_data);
> @@ -1345,7 +1430,7 @@ int pm_genpd_remove_device(struct generic_pm_domain *genpd,
>  	gpd_data = to_gpd_data(pdd);
>  	dev_pm_qos_remove_notifier(dev, &gpd_data->nb);
>  
> -	mutex_lock(&genpd->lock);
> +	genpd_lock(genpd);
>  
>  	if (genpd->prepared_count > 0) {
>  		ret = -EAGAIN;
> @@ -1360,14 +1445,14 @@ int pm_genpd_remove_device(struct generic_pm_domain *genpd,
>  
>  	list_del_init(&pdd->list_node);
>  
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  
>  	genpd_free_dev_data(dev, gpd_data);
>  
>  	return 0;
>  
>   out:
> -	mutex_unlock(&genpd->lock);
> +	genpd_unlock(genpd);
>  	dev_pm_qos_add_notifier(dev, &gpd_data->nb);
>  
>  	return ret;
> @@ -1388,12 +1473,24 @@ int pm_genpd_add_subdomain(struct generic_pm_domain *genpd,
>  	    || genpd == subdomain)
>  		return -EINVAL;
>  
> +	/*
> +	 * If the domain can be powered on/off in an IRQ safe
> +	 * context, ensure that the subdomain can also be
> +	 * powered on/off in that context.
> +	 */
> +	if (genpd->irq_safe && !subdomain->irq_safe) {
> +		WARN("Sub-domain (%s) in an IRQ-safe domain (%s)"
> +				"have to be IRQ safe\n",

s/have/has/

> +				subdomain->name, genpd->name);
> +		return -EINVAL;
> +	}
> +

Kevin