Re: [PATCH v3 5/5] powernv:cpufreq: Implement the driver->get() method

[Gautham R Shenoy <ego@linux.vnet.ibm.com>]

On Fri, Mar 21, 2014 at 03:01:29PM +0530, Viresh Kumar wrote:
> On Thu, Mar 20, 2014 at 5:41 PM, Gautham R. Shenoy
> <ego@linux.vnet.ibm.com> wrote:
> > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> >
> > The current frequency of a cpu is reported through the sysfs file
> > cpuinfo_cur_freq. This requires the driver to implement a
> > "->get(unsigned int cpu)" method which will return the current
> > operating frequency.
> >
> > Implement a function named powernv_cpufreq_get() which reads the local
> > pstate from the PMSR and returns the corresponding frequency.
> >
> > Set the powernv_cpufreq_driver.get hook to powernv_cpufreq_get().
> >
> > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> > ---
> >  drivers/cpufreq/powernv-cpufreq.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> 
> Please merge these fixups with the first patch which is creating the driver.
> I understand that a different guy has created this patch and so wanted
> to have a patch on his name but its really difficult to review this
way.

Heh! Well, that wasn't the reason why this was sent out as a separate
patch, but never mind. Though I don't understand why it would be
difficult to review the patch though.

> Better add your signed-off in the first patch instead. Sending such changes
> once the driver is mainlined looks fine.

Sure, this makes sense.

> 
> > diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> > index 46bee8a..ef6ed8c 100644
> > --- a/drivers/cpufreq/powernv-cpufreq.c
> > +++ b/drivers/cpufreq/powernv-cpufreq.c
> > @@ -206,6 +206,43 @@ static inline void set_pmspr(unsigned long sprn, unsigned long val)
> >         BUG();
> >  }
> >
> > +/*
> > + * Computes the current frequency on this cpu
> > + * and stores the result in *ret_freq.
> > + */
> > +static void powernv_read_cpu_freq(void *ret_freq)
> > +{
> > +       unsigned long pmspr_val;
> > +       s8 local_pstate_id;
> > +       int *cur_freq, freq, pstate_id;
> > +
> > +       cur_freq = (int *)ret_freq;
> 
> You don't need cur_freq variable at all..

I don't like it either. But the compiler complains without this hack
:-(

> 
> > +       pmspr_val = get_pmspr(SPRN_PMSR);
> > +
> > +       /* The local pstate id corresponds bits 48..55 in the PMSR.
> > +         * Note: Watch out for the sign! */
> > +       local_pstate_id = (pmspr_val >> 48) & 0xFF;
> > +       pstate_id = local_pstate_id;
> 
> similarly local_pstate_id

well, I am interested in the bits 48..55 of pmspr_val. That's the
pstate_id which can be negative. So I'll like to keep
local_pstate_id. 
> 
> > +
> > +       freq = pstate_id_to_freq(pstate_id);
> > +       pr_debug("cpu %d pmsr %lx pstate_id %d frequency %d \n",
> > +               smp_processor_id(), pmspr_val, pstate_id, freq);
> > +       *cur_freq = freq;
> 
> Move above print here after a blank line. Also remove freq variable as
> well and use *cur_freq directly.. And then you can rename it to freq
as well.

We can get rid of freq and use *cur_freq in its place.


Thanks for the detailed review.

--
Regards
gautham.