Re: [RFC PATCH v6 5/9] thermal: extend the cooling device API to include power information

[Javi Merino <javi.merino@arm.com>]

On Tue, Dec 23, 2014 at 03:14:11PM +0000, Eduardo Valentin wrote:
> Hi Javi
> 
> On Fri, Dec 05, 2014 at 07:04:16PM +0000, Javi Merino wrote:
> > Add three optional callbacks to the cooling device interface to allow
> > them to express power.  In addition to the callbacks, add helpers to
> > identify cooling devices that implement the power cooling device API.
> > 
> > Cc: Zhang Rui <rui.zhang@intel.com>
> > Cc: Eduardo Valentin <edubezval@gmail.com>
> > Signed-off-by: Javi Merino <javi.merino@arm.com>
> > ---
> >  Documentation/thermal/power_allocator.txt | 27 ++++++++++++++++++++++
> >  drivers/thermal/thermal_core.c            | 38 +++++++++++++++++++++++++++++++
> >  include/linux/thermal.h                   | 12 ++++++++++
> >  3 files changed, 77 insertions(+)
> >  create mode 100644 Documentation/thermal/power_allocator.txt
> > 
> > diff --git a/Documentation/thermal/power_allocator.txt b/Documentation/thermal/power_allocator.txt
> > new file mode 100644
> > index 000000000000..d3bb79050c27
> > --- /dev/null
> > +++ b/Documentation/thermal/power_allocator.txt
> > @@ -0,0 +1,27 @@
> > +Cooling device power API
> > +========================
> 
> Readers of this file need extra context here, IMO.

Patch 7 adds text before and after this section that provides that
context.

> > +
> > +Cooling devices controlled by this governor must supply the additional
> 
> What governor? the files says power allocator, and the title says,
> cooling device power API...

Correct, because that's added in the patch that introduces the power
allocator governor.  Therefore, it's not a problem for the readers of
this file but for the readers of the patches.  I can move this hunk to
patch 7 and introduce all the documentation at once if you think
that's clearer.

> > +"power" API in their `cooling_device_ops`.  It consists on three ops:
> > +
> 
> 
> 
> > +1. u32 get_actual_power(struct thermal_cooling_device *cdev);
> > +@cdev: The `struct thermal_cooling_device` pointer
> > +
> > +`get_actual_power()` returns the power currently consumed by the
> > +device in milliwatts.
> > +
> > +2. u32 state2power(struct thermal_cooling_device *cdev, unsigned long
> > +        state);
> > +@cdev: The `struct thermal_cooling_device` pointer
> > +@state: A cooling device state
> > +
> > +Convert cooling device state @state into power consumption in
> > +milliwatts.
> > +
> > +3. unsigned long power2state(struct thermal_cooling_device *cdev,
> > +        u32 power);
> > +@cdev: The `struct thermal_cooling_device` pointer
> > +@power: power in milliwatts
> > +
> > +Calculate a cooling device state that would make the device consume at
> > +most @power mW.
> 
> I believe it would be more helpful if you could provide extra context in
> which the above functions are called, and for what.

Ok, will do.

> > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> > index 9021cb72a13a..c490f262ea7f 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -866,6 +866,44 @@ emul_temp_store(struct device *dev, struct device_attribute *attr,
> >  static DEVICE_ATTR(emul_temp, S_IWUSR, NULL, emul_temp_store);
> >  #endif/*CONFIG_THERMAL_EMULATION*/
> >  
> > +/**
> > + * power_actor_get_max_power() - get the maximum power that a cdev can consume
> > + * @cdev:	pointer to &thermal_cooling_device
> > + *
> > + * Calculate the maximum power consumption in milliwats that the
> > + * cooling device can currently consume.  If @cdev doesn't support the
> > + * power_actor API, this function returns 0.
> > + */
> > +u32 power_actor_get_max_power(struct thermal_cooling_device *cdev)
> > +{
> > +	if (!cdev_is_power_actor(cdev))
> > +		return 0;
> > +
> > +	return cdev->ops->state2power(cdev, 0);
> > +}
> > +
> > +/**
> > + * power_actor_set_power() - limit the maximum power that a cooling device can consume
> > + * @cdev:	pointer to &thermal_cooling_device
> > + * @power:	the power in milliwatts
> > + *
> > + * Set the cooling device to consume at most @power milliwatts.
> > + *
> > + * Returns: 0 on success, -EINVAL if the cooling device does not
> > + * implement the power actor API or -E* for other failures.
> > + */
> > +int power_actor_set_power(struct thermal_cooling_device *cdev, u32 power)
> > +{
> > +	unsigned long state;
> > +
> > +	if (!cdev_is_power_actor(cdev))
> > +		return -EINVAL;
> > +
> > +	state = cdev->ops->power2state(cdev, power);
> > +
> > +	return cdev->ops->set_cur_state(cdev, state);
> > +}
> > +
> >  static DEVICE_ATTR(type, 0444, type_show, NULL);
> >  static DEVICE_ATTR(temp, 0444, temp_show, NULL);
> >  static DEVICE_ATTR(mode, 0644, mode_show, mode_store);
> > diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> > index 2c14ab1f5c0d..1155457caf52 100644
> > --- a/include/linux/thermal.h
> > +++ b/include/linux/thermal.h
> > @@ -142,6 +142,9 @@ struct thermal_cooling_device_ops {
> >  	int (*get_max_state) (struct thermal_cooling_device *, unsigned long *);
> >  	int (*get_cur_state) (struct thermal_cooling_device *, unsigned long *);
> >  	int (*set_cur_state) (struct thermal_cooling_device *, unsigned long);
> > +	u32 (*get_actual_power) (struct thermal_cooling_device *);
> > +	u32 (*state2power) (struct thermal_cooling_device *, unsigned long);
> > +	unsigned long (*power2state) (struct thermal_cooling_device *, u32);
> >  };
> >  
> >  struct thermal_cooling_device {
> > @@ -322,6 +325,15 @@ void thermal_zone_of_sensor_unregister(struct device *dev,
> >  }
> >  
> >  #endif
> > +
> > +static inline bool cdev_is_power_actor(struct thermal_cooling_device *cdev)
> > +{
> 
> What would happen if one pass cdev == NULL?

Is it really worth checking it here instead of just making the caller
pass a valid cdev?  There are a number of functions in the thermal
framework that don't check for valid cdevs or thermal zone pointers
and I don't see why this one is different.

> > +	return cdev->ops->get_actual_power && cdev->ops->state2power &&
> > +		cdev->ops->power2state;
> > +}
> > +
> > +u32 power_actor_get_max_power(struct thermal_cooling_device *);
> > +int power_actor_set_power(struct thermal_cooling_device *, u32);
> >  struct thermal_zone_device *thermal_zone_device_register(const char *, int, int,
> >  		void *, struct thermal_zone_device_ops *,
> >  		const struct thermal_zone_params *, int, int);
> 
> I am assuming the above two new functions are expected to be used also
> outside thermal core, right? If yes, I'd suggest exporting them. 

I don't expect it for the time being.  Wouldn't it be preferable to
export them when its needed instead?

Cheers,
Javi