Re: [RFC Add in_use attribute] Let the driver know if it's in use

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Thursday 16 April 2009, Michael Trimarchi wrote:
> Drivers on embedded systems would be smart enough
> to know that some of the devices should remain powered up, because
> they could still be useful even when the CPU wasn't running.
> The patch add the in_use attribute, that it can be used by the
> the drivers to avoid power down during suspend.

OK, so the idea is that in_use will be set by the user space for devices that
shouldn't be suspended.  Is this correct?

Assuming it is, I'd call the flag 'in_use' rather than 'is_inuse'.  Also, if
may_inuse is supposed to mean that we can set in_use for this device, I'd call
it 'in_use_valid', I'd make it be unset by default and I'd allow the driver to
unset it if it is going to react to 'in_use'.

> Signed-off-by: Michael Trimarchi <trimarchi@gandalf.sssup.it>
> Cc: "Alan Stern" <stern@rowland.harvard.edu>
> Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
> Cc: "Pavel Mackek" <pavel@ucw.cz>
> Cc: "Len Brown" <lenb@kernel.org>
> 
> ---
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index e73c92d..d67043b 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1124,6 +1124,49 @@ static struct device *next_device(struct klist_iter *i)
>  }
>  
>  /**
> + * device_visit_subtree - device subtree iterator.
> + * @root: root struct device.
> + * @data: data for the callback.
> + * @fn: function to be called for each device.
> + *
> + * Iterate the @parent's subtree devices, and call @fn for each,
> + * passing it @data.
> + *
> + */

Hmm, I'm not sure ig Greg is going to like it.

> +void device_visit_subtree(struct device *root, void *data,
> +			  int (*fn)(struct device *dev, void *data))
> +{
> +	struct klist_iter i;
> +	struct device *parent = root;

I'd call it 'current' or 'cur';

> +	struct device *child = NULL;
> +	int error;
> +
> +	klist_iter_init(&parent->p->klist_children, &i);
> +move_down:
> +	error = fn(parent, data);
> +	if (error && parent != root)

Shouldn't the iteration break on error?

> +		goto move_up;
> +
> +	pr_debug("device: '%s': %s\n", dev_name(parent), __func__);
> +
> +	child = next_device(&i);
> +	if (child) {
> +		parent = child;
> +		goto move_down;
> +	}
> +move_up:
> +	klist_iter_exit(&i);
> +	if (parent != root) {
> +		klist_iter_init_node(&parent->parent->p->klist_children, &i,
> +				     &parent->p->knode_parent);
> +		parent = next_device(&i);
> +		if (parent)
> +			goto move_down;
> +		klist_iter_exit(&i);
> +	}

Please find a way to reduce the number of gotos in this function.

Besides, I'm not sure if it's really necessary.  What's wrong with using
simply device_for_each_child() instead?

> +}
> +
> +/**
>   * device_for_each_child - device child iterator.
>   * @parent: parent struct device.
>   * @data: data for the callback.
> @@ -1207,6 +1250,7 @@ int __init devices_init(void)
>  	return -ENOMEM;
>  }
>  
> +EXPORT_SYMBOL_GPL(device_visit_subtree);
>  EXPORT_SYMBOL_GPL(device_for_each_child);
>  EXPORT_SYMBOL_GPL(device_find_child);
>  
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 69b4ddb..00ad150 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -64,6 +64,45 @@ void device_pm_unlock(void)
>  	mutex_unlock(&dpm_list_mtx);
>  }
>  
> +int device_set_may_inuse_enable(struct device *dev, void *data)

What exactly is the purpose of this function?

> +{
> +	pr_debug("PM: Device change in use status: %s\n", dev_name(dev));
> +
> +	/* if the device is suspend the subtree is in may_suspend status */
> +	if (dev->power.is_inuse)
> +		goto out;

   return 1; ?

> +
> +	dev->power.may_inuse = (unsigned int)data;

Can this conversion be avoided?

> +	return 0;
> +out:
> +	/* cut the entire subtree */
> +	return 1;
> +}
> +
> +/**
> + *	device_set_inuse_enable - Mark the device as used by userspace
> + *	application
> + */
> +int device_set_inuse_enable(struct device *dev, int enable)

We have bool for things like 'enable'.

> +{
> +	mutex_lock(&dpm_list_mtx);
> +
> +	/* the new status is equal the old one */
> +	if (dev->power.is_inuse == enable)
> +		goto out;
> +
> +	dev->power.is_inuse = enable;
> +
> +	/* Update device children to set the in use status */
> +	device_visit_subtree(dev, (void *)enable,
> +				device_set_may_inuse_enable);

Why not do:

    if (dev->power.in_use != enable) {
         dev->power.in_use = enable;
         device_visit_subtree(dev, (void *)enable, device_set_may_inuse_enable);
    }

Also, I think this 'enable' conversion isn't really necessary.  You can use two
separate helper functions for setting and unsetting and pass NULL as the second
argument.

> +
> +out:
> +	mutex_unlock(&dpm_list_mtx);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(device_set_inuse_enable);
> +
>  /**
>   *	device_pm_add - add a device to the list of active devices
>   *	@dev:	Device to be added to the list
> @@ -78,6 +117,13 @@ void device_pm_add(struct device *dev)
>  		if (dev->parent->power.status >= DPM_SUSPENDING)
>  			dev_warn(dev, "parent %s should not be sleeping\n",
>  				 dev_name(dev->parent));
> +		if (device_is_inuse(dev->parent)) {
> +			mutex_unlock(&dpm_list_mtx);
> +			/* if the parent has suspend disable, propagate it
> +			 * to the new child */
> +			device_set_may_inuse_enable(dev, (void *)1);

The conversion is just terrible.  I'd very much prefer it to be
device_set_in_use_possible_enable(dev, true).

> +			mutex_lock(&dpm_list_mtx);
> +		}
>  	} else if (transition_started) {
>  		/*
>  		 * We refuse to register parentless devices while a PM
> diff --git a/drivers/base/power/power.h b/drivers/base/power/power.h
> index c7cb4fc..e7d21bb 100644
> --- a/drivers/base/power/power.h
> +++ b/drivers/base/power/power.h
> @@ -3,6 +3,11 @@ static inline void device_pm_init(struct device *dev)
>  	dev->power.status = DPM_ON;
>  }
>  
> +static inline int device_is_inuse(struct device *dev)
> +{
> +	return dev->power.is_inuse || dev->power.may_inuse;
> +}

OK, so what's the meaning of is_inuse and may_inuse?

>  #ifdef CONFIG_PM_SLEEP
>  
>  /*
> diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> index 596aeec..45d7f60 100644
> --- a/drivers/base/power/sysfs.c
> +++ b/drivers/base/power/sysfs.c
> @@ -43,6 +43,34 @@
>  static const char enabled[] = "enabled";
>  static const char disabled[] = "disabled";
>  
> +static ssize_t inuse_show(struct device *dev, struct device_attribute *attr,
> +				char *buf)
> +{
> +	return sprintf(buf, "%s\n", device_is_inuse(dev)
> +		? enabled : disabled);
> +}
> +
> +static ssize_t
> +inuse_store(struct device *dev, struct device_attribute *attr,
> +		const char *buf, size_t n)
> +{
> +	char *cp;
> +	int len = n;
> +
> +	cp = memchr(buf, '\n', n);
> +	if (cp)
> +		len = cp - buf;
> +	if (len == sizeof enabled - 1
> +			&& strncmp(buf, enabled, sizeof enabled - 1) == 0)
> +		device_set_inuse_enable(dev, 1);
> +	else if (len == sizeof disabled - 1
> +			&& strncmp(buf, disabled, sizeof disabled - 1) == 0)
> +		device_set_inuse_enable(dev, 0);
> +	else
> +		return -EINVAL;
> +	return n;
> +}
> +
>  static ssize_t
>  wake_show(struct device * dev, struct device_attribute *attr, char * buf)
>  {
> @@ -76,10 +104,11 @@ wake_store(struct device * dev, struct device_attribute *attr,
>  }
>  
>  static DEVICE_ATTR(wakeup, 0644, wake_show, wake_store);
> -
> +static DEVICE_ATTR(in_use, 0644, inuse_show, inuse_store);
>  
>  static struct attribute * power_attrs[] = {
>  	&dev_attr_wakeup.attr,
> +	&dev_attr_in_use.attr,
>  	NULL,
>  };
>  static struct attribute_group pm_attr_group = {
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 2918c0e..84a2bab 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -496,6 +496,9 @@ extern struct device *device_find_child(struct device *dev, void *data,
>  extern int device_rename(struct device *dev, char *new_name);
>  extern int device_move(struct device *dev, struct device *new_parent,
>  		       enum dpm_order dpm_order);
> +extern int device_set_inuse_enable(struct device *dev, int enable);
> +extern void device_visit_subtree(struct device *root, void *data,
> +				 int (*fn)(struct device *dev, void *data));
>  
>  /*
>   * Root device objects for grouping under /sys/devices
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 1d4e2d2..85f3fb2 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -319,6 +319,9 @@ struct dev_pm_info {
>  	pm_message_t		power_state;
>  	unsigned		can_wakeup:1;
>  	unsigned		should_wakeup:1;
> +	unsigned		is_inuse:1;
> +	unsigned		may_inuse:1;
> +
>  	enum dpm_state		status;		/* Owned by the PM core */
>  #ifdef	CONFIG_PM_SLEEP
>  	struct list_head	entry;

Thanks,
Rafael