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

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

Hi Eduardo,

On Mon, Jan 05, 2015 at 09:04:09PM +0000, Eduardo Valentin wrote:
> On Mon, Jan 05, 2015 at 03:37:10PM +0000, Javi Merino wrote:
> > 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.
> > 
> 
> Thinking of the atomicity of each patch/commit, I would prefer you to
> move all documentation to a single patch then.

Ok, I'll move it to the patch that introduces the power allocator.

[...]
> > > > 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.
> 
> I don't know, maybe we should fix those misbehaving functions then? Can
> you please point them out?

This is not an exhaustive list but a quick grep only in thermal_core.c
yields:
  - get_tz_trend() doesn't check tz
  - get_thermal_instance() doesn't check tz or cdev
  - thermal_zone_device_update() doesn't check tz
  - thermal_zone_bind_cooling_device() doesn't check tz or cdev
  - thermal_zone_unbind_cooling_device() doesn't check tz or cdev
  - thermal_cdev_update() doesn't check cdev

> > > > +	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?
> 
> I believe functions in this header are exported. For functions used
> inside thermal core and code that goes builtin always, they go into
> drivers/thermal/thermal_core.h, and are not exported.

Ok, I'll move them to drivers/thermal/thermal_core.h .

Cheers,
Javi