Guarantee udelay(N) spins at least N microseconds

[Russell King - ARM Linux]

On Fri, Apr 10, 2015 at 10:01:35PM +0200, Mason wrote:
> There is, however, an important difference between loop-based
> delays and timer-based delays; CPU frequencies typically fall
> in the 50-5000 MHz range, while timer frequencies typically
> span tens of kHz up to hundreds of MHz. For example, 90 kHz
> is sometimes provided in multimedia systems (MPEG TS).

Why would you want to use such a slowly clocked counter for something
which is supposed to be able to produce delays in the micro-second and
potentially the nanosecond range?

get_cycles(), which is what the timer based delay is based upon, is
supposed to be a _high resolution counter_, preferably running at
the same kind of speeds as the CPU, though with a fixed clock rate.
It most definitely is not supposed to be in the kHz range.

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