[PATCH v2 2/2] ARM: delay: allow timer-based delay implementation to be selected

Will Deacon will.deacon at arm.com
Fri Jul 13 08:08:57 EDT 2012

On Fri, Jul 13, 2012 at 01:04:27PM +0100, Shilimkar, Santosh wrote:
> On Fri, Jul 13, 2012 at 4:43 PM, Will Deacon <will.deacon at arm.com> wrote:
> > I was anticipating that the platform would set the initial loops_per_jiffy
> > value if it requires udelays before loop calibration and the default of 4k
> > is wildly off.
> >
> > If people need loops_per_jiffy to be updated at the same time as lpj_fine,
> > I can post that as a separate patch (below) as Russell has merged v2 of these
> > patches into his delay branch. That said, I'd certainly like to know if this
> > is actually a real problem (and can't be solved by choosing a compromise value
> > as the initial loops_per_jiffy). I think Shinya was doing some tests so
> > I'll wait to see how those went.
> >
> I just tried the suggested change + two patches.
> I haven't gone through the complete discussion but quick test of your patches
> on OMAP5, shows me, the BOGOMIPS is completely wrong. Looks like
> you are not updating the  'loops_per_jiffy' in the calibration loop.

What is your bogomips reading and what frequency is your architected timer
ticking at? loops_per_jiffy is updated by calibrate_delay in
init/calibrate.c so we shouldn't need to worry about that (the diff I posted
in my last email is just for udelay calls between switching to the timer and
doing the calibration).

> What Am I missing ?

Well, your bogomips number will probably be *much* lower than before, so
don't be surprised by that.


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