Re: [RFC 1/1] ARM: print MHz in /proc/cpuinfo

[Sudeep Holla]

On 08/06/16 20:31, Jon Mason wrote:
> On Wed, Jun 08, 2016 at 09:34:06AM +0100, Sudeep Holla wrote:
> > On 07/06/16 22:08, Jon Mason wrote:
> > > Query the CPU core clock in the device tree to determine the core clock
> > > speed.
> >
> > How do guarantee that it's the current frequency of the CPU ?
>
> I am basing it on the assumption (perhaps incorrect) that the clock in
> the CPU DT corresponds to the one determining the CPU clock rate.  And,
> that this clock rate is accurate in describing the speed at which the
> CPU is currently running.

As you already noticed, it's not always correct.

[..]

> > What if they just don't have in DT but have DVFS support ?
>
> This can be extended to cover DVFS or SMC calls or anything else.
> This was simply a first step to cover what appeared to be the most
> prevalent case.

Using DVFS/CPUFreq makes this DT based approach irrelevant.

> > Also whey do we need this support when the user-space can query the
> > CPUFreq sysfs which is more accurate and maintains the current running
> > frequency ?
>
> This is exactly what x86 is doing to provide its value in
> /proc/cpuinfo.  I could easily augment this patch to call
> cpufreq_quick_get(), if it returns 0, then call clk_get_rate().  If
> both return 0, then simply not print out anything (which would cover
> all of the possibilities).  Or, I could have it just call
> cpufreq_quick_get() to get the value.

Agree x86 has, may be for legacy reasons. It even has CPUFreq sysfs
entries which is architecture agnostic while /proc/cpuinfo is more
architecture based. So applications that want to be portable across
architectures must choose the generic CPUFreq sysfs path rather than
some x86 based cpuinfo.

--
Regards,
Sudeep