Re: [PATCH V2] cpufreq: Disallow ->resolve_freq() for drivers providing ->target_index()

From: Steve Muckle
Date: Thu Jul 21 2016 - 20:34:23 EST

On Fri, Jul 22, 2016 at 02:18:54AM +0200, Rafael J. Wysocki wrote:
> > My thinking was that one of these two would be preferable:
> >
> > - Forcing ->target() drivers to install a ->resolve_freq callback,
> > enforcing this at cpufreq driver init time.
> That would have been possible, but your series didn't do that.
> > My understanding is
> > ->target() drivers are deprecated anyway
> No, they aren't.

Ok. I didn't follow Documentation/cpu-freq/cpu-drivers.txt section 1.5
then - it suggests something about target() is deprecated, perhaps it's
out of date.

> There simply are cases in which frequency tables are not workable
> (like the ACPI CPPC one).

Sure that makes sense.

> > and theren't aren't many of
> > them, though I don't know offhand exactly how many or how hard it
> > would be to do for each one.
> >
> > - Forcing callers (schedutil in this case) to check that either
> > ->target() or ->resolve_freq() is implemented. It means
> > catching and scrutinizing future callers of resolve_freq.
> But that doesn't reduce the number of checks in cpufreq_driver_resolve_freq().
> There still are three choices in there: return a frequency from the
> table (if present), or call ->resolve_freq (if implemented), or return
> target_freq (as the last resort).

Sorry, that should've been "check that either ->target_index() or
->resolve_freq() is implemented."

Implementing resolve_freq for the target() drivers and requiring it at
driver init time is probably the better way to go though. Perhaps I can
work on this at some point.