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From: Roland Dreier <rdreier@cisco.com>
To: Timur Tabi <timur@freescale.com>
Subject: Re: [PATCH v5] introduce macro spin_event_timeout()
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Date: Tue, 10 Mar 2009 22:09:59 -0700
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	(Timur Tabi's message of "Tue, 10 Mar 2009 19:22:28 -0500")
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Cc: Scott Wood <scottwood@freescale.com>, linuxppc-dev@ozlabs.org
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 > Alan did have one valid point though.  Determining how long to loop
 > for is architecture-specific.  Using jiffies is bad, because even one
 > jiffy is too long.  Adding a udelay() inside the loop means that it
 > only checks he condition every microsecond.  So the real solution is
 > to use keep looping until a certain amount of time has passed.  This
 > means using an architecture-specific timebase register.

Are there really cases where spinning for 1 jiffy is too long of a
timeout?  It might make sense for the parameter passed in to be in terms
of microseconds but I have a hard time coming up with a case where
having the real timeout be 40 msecs or whatever 1 jiffy ends up being is
a real problem -- after all, this helper is intended for the case where
we expect the condition to become true much sooner than the worst case.

 - R.