[PATCHv2] omap2+: pm: cpufreq: Fix loops_per_jiffy calculation

[Russell King - ARM Linux]

On Tue, Jun 28, 2011 at 03:45:22PM -0700, Santosh Shilimkar wrote:
> The udelay code doesn't use the per-cpu lpj variable. It uses the global
> lpj. Secondly the calibration of no. of loops to be done is
> precalculateed so overwrite shouldn't impact the scenario you mentioned.
>
> Though it has an issue where, pre-calculated loops can become short/long
> based on new clock change which impacts both CPU's on OMAP, when the  
> other CPU is in in the middle of u-delay routine..

And there's also the issue where you can start a udelay loop on one CPU,
be pre-empted and end up running it on a different CPU running at a
different speed.

The thing to bear in mind is that udelays are approximate at best - I did
some investigation into the accuracy of the loops_per_jiffy calculation,
and it _will_ produce shorter delays than expected by the fact that
what is being calibrated is the udelay() loop _plus_ the timer interrupt
overhead.