Re: [linux-pm] [patch/rft 2.6.17-rc2] swsusp resume must not device_suspend()

[David Brownell <david-b@pacbell.net>]

On Tuesday 25 April 2006 6:16 pm, Nigel Cunningham wrote:
> Hi.
> 
> On Wednesday 26 April 2006 09:55, David Brownell wrote:
> > On Tuesday 25 April 2006 3:18 pm, Nigel Cunningham wrote:
> > > I saw the 2 suspends, 1 resume comment in another part of the thread, but
> > > don't believe a driver would be able to detect that 2 suspends and 1
> > > resume call had been made - at least not without some non volatile ram.
> >
> > The extra suspend is just IMO a symptom of sloppiness, like a "here may be
> > bugs" sign.  Not necessarily an issue in its own right.
> >
> > In fact if you count carefully, it's three suspends and one resume:  one
> > suspend before calling swsusp_resume, one inside swsusp_resume -- replaced
> > by my patch -- and a correctly matched pair in the kernel being resumed.
> 
> That doesn't sound right. Let' see - where's this third one?

I see your point ... device_suspend() and device_power_down() really
do the same thing, but to different sets of devices.  A nastily deceptive
naming convention that I may want to fix someday.

So it's not quite fair counting those separately.  Three suspend calls,
sure ... but only two per device.


> > Also, about non-volatile RAM.  Not necessary ... the device hardware holds
> > all the relevant state.  The problem is that swsusp is now trashing it with
> > those suspend calls before resuming the real kernel.  On the plus side, we
> > already have code being used to resolve the identical issue for kexec(),
> > and all my patch does is to use it.
> 
> If devices really do get powered down, then they won't retain the state. If 
> they don't actually powerdown, then I see your point.

While the system is restarting into the snapshot, there's no powerdown.
(Because device_power_down doesn't actually power down devices.)  Q.E.D.

- Dave



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