Re: [PATCH v7] cpufreq: Add SFI based cpufreq driver support

["Kasagar, Srinidhi" <srinidhi.kasagar@intel.com>]

On Wed, Dec 17, 2014 at 05:12:43PM -0500, Len Brown wrote:
> >> policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
> >
> > But we know the transition latency of this system. Why should we
> > claim it as "unknown"? The sfi_freq_table_entry has latency
> > field - does it not make irrelevant then?
> 
> I wrote the SFI spec.
> If I did it again, I would not include the latency field in the FREQ table,
> because Linux does not need it.
> 
> >> ondemand will compare this to TRANSITION_LATENCY_LIMIT (10 * 1000 * 1000)
> >> and since -1 is less than 10,000,000; it will be happy.
> >>
> >> > +       for (i = 0; i < num_freq_table_entries; i++) {
> >> > +               /* detect transition latency */
> >> > +               if ((sfi_cpufreq_array[i].latency * 1000) >
> >> > +                   policy->cpuinfo.transition_latency)
> >> > +                       policy->cpuinfo.transition_latency =
> >> > +                               sfi_cpufreq_array[i].latency * 1000;
> >>
> >> delete above 5 lines.  every SFI system will have latency
> >> plenty lower than that required by ondemand governor.
> 
> There is effectively no customer for the information being provided,
> as there are only two possible outcomes:
> 
> 1. The largest value in the table is < 10ms, and ondemand loads
> 2. The largest value in the table is > 10ms and ondemand fails to load.
> #1 is how it should always work on all known SFI platforms.
> #2 is a firmware bug.
> 
> Well, we can do #1 with 1 line, and at the same time eliminate
> exposure to firmware bugs in #2.

Ok, as we know the latency of this system (as 100 us), I will hardcode this
with 1 line and remove the rest of detection stuff..

Srinidhi