Re: [PATCH/RFC] via-pmu: remove mdelays from suspend/resume code

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2008-04-04 at 21:21 +0200, Johannes Berg wrote:
> On Fri, 2008-04-04 at 10:20 -0700, Brad Boyer wrote:
> > On Thu, Apr 03, 2008 at 05:44:44PM +0200, Johannes Berg wrote:
> > > I don't see a reason for either of those mdelay()s, is there any? Works
> > > fine for me without them...
> > 
> > Which hardware revisions did you test? I suspect the mdelay calls were
> > added to work around timing issues in one of the older PMU chips. Some
> > of them are very timing sensitive, and sleep in particular is basically
> > a pile of steps that got hacked until they worked on older systems.
> 
> Mine's a 5,6 powerbook with PMU firmware 0x0c. The mdelay(100) seems
> fairly large though for a point where we're out of pmu code already, and
> the other one doesn't really seem too pmu related anyway. In any case,
> just wanted to float that, don't see a particular need for it.

One of those was meant to let devices settle. The reason is that when
waking from sleep, a lot of HW on the mobo is actually powered up (it
was down during sleep). This delay comes from half paranoia / half
experience, and is meant to ensure all those chips got a chance to
settle and complete their power-on reset sequence before we start
banging all over the place.

Cheers,
Ben.