Choosing between DELAY(useconds) and pause()
jhb at freebsd.org
Mon Sep 26 14:01:00 UTC 2011
On Friday, September 23, 2011 11:21:06 am Gavin Atkinson wrote:
> On Thu, 2011-09-22 at 20:07 +0200, Hans Petter Selasky wrote:
> > On Thursday 22 September 2011 19:55:23 David Somayajulu wrote:
> > > It appears that the pause() function cannot be used in driver functions
> > > which are invoked early in the boot process. Is there is a kernel api
> > > which a device driver can use to determine whether to use pause() or
> > > DELAY(), for delays which are say greater than 10hz - may be even 1 hz ?
> > Maybe you want to use something like this:
> > if (cold)
> > DELAY()
> > else
> > pause()
> > In your code.
> Note that this still shouldn't be done in your suspend/resume paths, as
> "cold" isn't set there, however there also appears to be no guarantee
> that pause() will ever return (as you could be running after the timer
> has been suspended, or before it resumes).
> I'm not sure what the correct answer is for suspend/resume code.
Hmmm, on x86 the timers are explicitly shutdown after the DEVICE_SUSPEND()
pass over the tree and re-enabled before DEVICE_RESUME(). Perhaps this has
changed in HEAD though with the eventtimers stuff. I do think it is best
however, to use DELAY() in the suspend/resume path always regardless.
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