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

[Nigel Cunningham <nigel@suspend2.net>]

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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?

			Real				Effective
SUSPEND

Pre-copy		suspend(freeze)		suspend(freeze)
			powerdown(freeze)	powerdown(freeze)

Post-copy		powerup
			resume

Powerdown	shutdown_prepare/kernel_power_off/...

RESUME

			bios & kernel init

Pre-restore		suspend(freeze)
			powerdown(freeze)

Post-restore	powerup			powerup
			resume			resume


> Raising two points:  (1) for those who think suspend is right, you can
> think of it as replacing one of the extra ones with
> kernel_restart_prepare(); and (2) not very much code interacts with that
> restart prep, that's a sane audit problem.
>
>
> 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.

Regards,

Nigel
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