linux-kernel - Re: [PATCH v4 4/5] thermal: power_allocator: don't require tzp to be present for the thermal zone

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Date:	Fri, 28 Aug 2015 17:28:08 +0100
From:	Javi Merino <javi.merino@....com>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Chung-yih Wang <cywang@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punit Agrawal <Punit.Agrawal@....com>,
	Eduardo Valentin <edubezval@...il.com>,
	Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH v4 4/5] thermal: power_allocator: don't require tzp to be
 present for the thermal zone

On Fri, Aug 28, 2015 at 03:18:20AM +0100, Daniel Kurtz wrote:
> On Wed, Aug 26, 2015 at 9:26 PM, Javi Merino <javi.merino@....com> wrote:
> > Thermal zones created using thermal_zone_device_create() may not have
> > tzp.  As the governor gets its parameters from there, allocate it while
> > the governor is bound to the thermal zone so that it can operate in it.
> > In this case, tzp is freed when the thermal zone switches to another
> > governor.
> >
> > Cc: Zhang Rui <rui.zhang@...el.com>
> > Cc: Eduardo Valentin <edubezval@...il.com>
> > Signed-off-by: Javi Merino <javi.merino@....com>
> > ---
> >
> > While this would be easier to do by just ignoring the thermal zone if
> > there was no tzp, I think the approach in this patch provides a better
> > behavior.
> 
> Why?
> Just ignoring the thermal zone seems reasonable and simpler.

>From the developer point of view, I agree that it's simpler.  What I
want to avoid is the system integrator getting different behaviors
based on the presence of tzp when the thermal zone was created.  If
the integrator was to configure this from userspace, they would only
be able to do so if the thermal zone was created with tzp.  I don't
like this distinction, I prefer the consistency from the user point of
view that this patch gives.

Cheers,
Javi

> >  drivers/thermal/power_allocator.c | 32 +++++++++++++++++++++++++++-----
> >  1 file changed, 27 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/thermal/power_allocator.c b/drivers/thermal/power_allocator.c
> > index 2dfb8ade4d1b..85ce0aac9a41 100644
> > --- a/drivers/thermal/power_allocator.c
> > +++ b/drivers/thermal/power_allocator.c
> > @@ -58,6 +58,8 @@ static inline s64 div_frac(s64 x, s64 y)
> >
> >  /**
> >   * struct power_allocator_params - parameters for the power allocator governor
> > + * @allocated_tzp:     whether we have allocated tzp for this thermal zone and
> > + *                     it needs to be freed on unbind
> >   * @err_integral:      accumulated error in the PID controller.
> >   * @prev_err:  error in the previous iteration of the PID controller.
> >   *             Used to calculate the derivative term.
> > @@ -70,6 +72,7 @@ static inline s64 div_frac(s64 x, s64 y)
> >   *                                     controlling for.
> >   */
> >  struct power_allocator_params {
> > +       bool allocated_tzp;
> >         s64 err_integral;
> >         s32 prev_err;
> >         int trip_switch_on;
> > @@ -530,8 +533,7 @@ static void allow_maximum_power(struct thermal_zone_device *tz)
> >   * Initialize the PID controller parameters and bind it to the thermal
> >   * zone.
> >   *
> > - * Return: 0 on success, -EINVAL if the thermal zone doesn't have tzp or -ENOMEM
> > - * if we ran out of memory.
> > + * Return: 0 on success, or -ENOMEM if we ran out of memory.
> >   */
> >  static int power_allocator_bind(struct thermal_zone_device *tz)
> >  {
> > @@ -539,13 +541,20 @@ static int power_allocator_bind(struct thermal_zone_device *tz)
> >         struct power_allocator_params *params;
> >         unsigned long control_temp;
> >
> > -       if (!tz->tzp)
> > -               return -EINVAL;
> > -
> >         params = kzalloc(sizeof(*params), GFP_KERNEL);
> >         if (!params)
> >                 return -ENOMEM;
> >
> > +       if (!tz->tzp) {
> > +               tz->tzp = kzalloc(sizeof(*tz->tzp), GFP_KERNEL);
> 
> Why bother to allocate this dummy struct?
> Can't we just leave tz->tzp as NULL, and do a NULL check where needed?
> 
> > +               if (!tz->tzp) {
> > +                       ret = -ENOMEM;
> > +                       goto free_params;
> > +               }
> > +
> > +               params->allocated_tzp = true;
> > +       }
> > +
> >         if (!tz->tzp->sustainable_power)
> >                 dev_warn(&tz->device, "power_allocator: sustainable_power will be estimated\n");
> >
> > @@ -562,11 +571,24 @@ static int power_allocator_bind(struct thermal_zone_device *tz)
> >         tz->governor_data = params;
> >
> >         return 0;
> > +
> > +free_params:
> > +       kfree(params);
> > +
> > +       return ret;
> >  }
> >
> >  static void power_allocator_unbind(struct thermal_zone_device *tz)
> >  {
> > +       struct power_allocator_params *params = tz->governor_data;
> > +
> >         dev_dbg(&tz->device, "Unbinding from thermal zone %d\n", tz->id);
> > +
> > +       if (params->allocated_tzp) {
> > +               kfree(tz->tzp);
> > +               tz->tzp = NULL;
> > +       }
> > +
> >         kfree(tz->governor_data);
> >         tz->governor_data = NULL;
> >  }
> > --
> > 1.9.1
> >
> 
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