Subject: Re: [PATCH v2 2/3] cpuidle:powernv: Add helper function to populate powernv idle states.

From: Gautham R Shenoy <[email-masked]>
Date: Wed, 2 Nov 2016 14:12:21 +0530

Hi Oliver,

Thanks for reviewing the patch!

On Tue, Nov 01, 2016 at 07:32:58PM +1100, Oliver O'Halloran wrote:
> On Thu, Oct 27, 2016 at 7:35 PM, Gautham R. Shenoy
> <[email-masked]> wrote:
> > From: "Gautham R. Shenoy" <[email-masked]>
> >
> > In the current code for powernv_add_idle_states, there is a lot of code
> > duplication while initializing an idle state in powernv_states table.
> >
> > Add an inline helper function to populate the powernv_states[] table for
> > a given idle state. Invoke this for populating the "Nap", "Fastsleep"
> > and the stop states in powernv_add_idle_states.
> >
> > Signed-off-by: Gautham R. Shenoy <[email-masked]>
> > ---
> >  drivers/cpuidle/cpuidle-powernv.c | 82 +++++++++++++++++++++++----------------
> >  include/linux/cpuidle.h           |  1 +
> >  2 files changed, 49 insertions(+), 34 deletions(-)
> >
> > diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> > index 7fe442c..11b22b9 100644
> > --- a/drivers/cpuidle/cpuidle-powernv.c
> > +++ b/drivers/cpuidle/cpuidle-powernv.c
> > @@ -167,6 +167,28 @@ static int powernv_cpuidle_driver_init(void)
> >         return 0;
> >  }
> >
> > +static inline void add_powernv_state(int index, const char *name,
> > +                                    unsigned int flags,
> > +                                    int (*idle_fn)(struct cpuidle_device *,
> > +                                                   struct cpuidle_driver *,
> > +                                                   int),
> > +                                    unsigned int target_residency,
> > +                                    unsigned int exit_latency,
> > +                                    u64 psscr_val)
> > +{
> > +       strncpy(powernv_states[index].name, name, CPUIDLE_NAME_LEN);
> > +       strncpy(powernv_states[index].desc, name, CPUIDLE_NAME_LEN);
> 
> If the supplied name is equal to CPUIDLE_NAME_LEN then strncpy() won't
> terminate the string. The least annoying fix is to memset() the whole
> structure to zero and set n to CPUIDLE_NAME_LEN - 1.

I will change this to use strlcpy as Paul suggested in the reply.

> 
> > +       powernv_states[index].flags = flags;
> > +       powernv_states[index].target_residency = target_residency;
> > +       powernv_states[index].exit_latency = exit_latency;
> > +       powernv_states[index].enter = idle_fn;
> > +
> > +       if (idle_fn != stop_loop)
> > +               return;
> 
> This can probably be deleted. The nap/sleep loops don't look at the
> psscr setting and you've passed in a dummy value of zero anyway.

The subsequent patch adds the missing bits to the psscr_val if we are
running on the older firmware. But in any case, as you rightly pointed
out we don't use psscr_table in nap/sleep loops. So this can go.

> 
> > +
> > +       stop_psscr_table[index] = psscr_val;
> > +}
> > +
> >  static int powernv_add_idle_states(void)
> >  {
> >         struct device_node *power_mgt;
> > @@ -236,6 +258,7 @@ static int powernv_add_idle_states(void)
> >                 "ibm,cpu-idle-state-residency-ns", residency_ns, dt_idle_states);
> >
> >         for (i = 0; i < dt_idle_states; i++) {
> > +               unsigned int exit_latency, target_residency;
> >                 /*
> >                  * If an idle state has exit latency beyond
> >                  * POWERNV_THRESHOLD_LATENCY_NS then don't use it
> > @@ -244,27 +267,30 @@ static int powernv_add_idle_states(void)
> >                 if (latency_ns[i] > POWERNV_THRESHOLD_LATENCY_NS)
> >                         continue;
> >
> > +               exit_latency = ((unsigned int)latency_ns[i]) / 1000;
> > +               target_residency = (!rc) ? ((unsigned int)residency_ns[i]) : 0;
> > +               /*
> > +                * Firmware passes residency values in ns.
> > +                * cpuidle expects it in us.
> > +                */
> > +               target_residency /= 1000;
> > +
> >                 /*
> >                  * Cpuidle accepts exit_latency and target_residency in us.
> 
> This comment says the same thing as the one above.

Will clean this up to reflect the state of the code.

> 
> >                  * Use default target_residency values if f/w does not expose it.
> >                  */
> >                 if (flags[i] & OPAL_PM_NAP_ENABLED) {
> > +                       target_residency = 100;
> 
> Hmm, the above comment says that we should only use the default value
> for target_residency if firmware hasn't provided a value. Is there a
> reason we always use the hard coded value?

Ah, good catch! I should be setting target_residency to the default
value only if it is not set by the firmware. Will fix this.

> 
> >                         /* Add NAP state */
> > -                       strcpy(powernv_states[nr_idle_states].name, "Nap");
> > -                       strcpy(powernv_states[nr_idle_states].desc, "Nap");
> > -                       powernv_states[nr_idle_states].flags = 0;
> > -                       powernv_states[nr_idle_states].target_residency = 100;
> > -                       powernv_states[nr_idle_states].enter = nap_loop;
> > +                       add_powernv_state(nr_idle_states, "Nap",
> > +                                         CPUIDLE_FLAG_NONE, nap_loop,
> > +                                         target_residency, exit_latency, 0);
> >                 } else if ((flags[i] & OPAL_PM_STOP_INST_FAST) &&
> >                                 !(flags[i] & OPAL_PM_TIMEBASE_STOP)) {
> > -                       strncpy(powernv_states[nr_idle_states].name,
> > -                               names[i], CPUIDLE_NAME_LEN);
> > -                       strncpy(powernv_states[nr_idle_states].desc,
> > -                               names[i], CPUIDLE_NAME_LEN);
> > -                       powernv_states[nr_idle_states].flags = 0;
> > -
> > -                       powernv_states[nr_idle_states].enter = stop_loop;
> > -                       stop_psscr_table[nr_idle_states] = psscr_val[i];
> > +                       add_powernv_state(nr_idle_states, names[i],
> > +                                         CPUIDLE_FLAG_NONE, stop_loop,
> > +                                         target_residency, exit_latency,
> > +                                         psscr_val[i]);
> >                 }
> >
> >                 /*
> > @@ -274,32 +300,20 @@ static int powernv_add_idle_states(void)
> >  #ifdef CONFIG_TICK_ONESHOT
> >                 if (flags[i] & OPAL_PM_SLEEP_ENABLED ||
> >                         flags[i] & OPAL_PM_SLEEP_ENABLED_ER1) {
> > +                       target_residency = 300000;
> 
> Same comment as above.
> 
> >                         /* Add FASTSLEEP state */
> > -                       strcpy(powernv_states[nr_idle_states].name, "FastSleep");
> > -                       strcpy(powernv_states[nr_idle_states].desc, "FastSleep");
> > -                       powernv_states[nr_idle_states].flags = CPUIDLE_FLAG_TIMER_STOP;
> > -                       powernv_states[nr_idle_states].target_residency = 300000;
> > -                       powernv_states[nr_idle_states].enter = fastsleep_loop;
> > +                       add_powernv_state(nr_idle_states, "FastSleep",
> > +                                         CPUIDLE_FLAG_TIMER_STOP,
> > +                                         fastsleep_loop,
> > +                                         target_residency, exit_latency, 0);
> >                 } else if ((flags[i] & OPAL_PM_STOP_INST_DEEP) &&
> >                                 (flags[i] & OPAL_PM_TIMEBASE_STOP)) {
> > -                       strncpy(powernv_states[nr_idle_states].name,
> > -                               names[i], CPUIDLE_NAME_LEN);
> > -                       strncpy(powernv_states[nr_idle_states].desc,
> > -                               names[i], CPUIDLE_NAME_LEN);
> > -
> > -                       powernv_states[nr_idle_states].flags = CPUIDLE_FLAG_TIMER_STOP;
> > -                       powernv_states[nr_idle_states].enter = stop_loop;
> > -                       stop_psscr_table[nr_idle_states] = psscr_val[i];
> > +                       add_powernv_state(nr_idle_states, names[i],
> > +                                         CPUIDLE_FLAG_TIMER_STOP, stop_loop,
> > +                                         target_residency, exit_latency,
> > +                                         psscr_val[i]);
> >                 }
> >  #endif
> > -               powernv_states[nr_idle_states].exit_latency =
> > -                               ((unsigned int)latency_ns[i]) / 1000;
> > -
> > -               if (!rc) {
> > -                       powernv_states[nr_idle_states].target_residency =
> > -                               ((unsigned int)residency_ns[i]) / 1000;
> > -               }
> > -
> >                 nr_idle_states++;
> >         }
> >  out:
> > diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> > index bb31373..c4e10f8 100644
> > --- a/include/linux/cpuidle.h
> > +++ b/include/linux/cpuidle.h
> > @@ -62,6 +62,7 @@ struct cpuidle_state {
> >  };
> >
> >  /* Idle State Flags */
> > +#define CPUIDLE_FLAG_NONE       (0x00)
> >  #define CPUIDLE_FLAG_COUPLED   (0x02) /* state applies to multiple cpus */
> >  #define CPUIDLE_FLAG_TIMER_STOP (0x04)  /* timer is stopped on this state */
> >
> > --
> > 1.9.4
> >
> 
> Looks good otherwise.
> 
> Reviewed-by: Oliver O'Halloran <[email-masked]>

Thanks again!

--
Regards
gautham.