Re: [PATCH 2/2] Fix console handling during suspend/resume

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > Here's what you actually did say:
> > ---------
> >
> > > To have DMAs stopped, you need to "freeze" the devices.
> > 
> > No you don't. 
> > 
> > You need to stop the high-level _queues_, but that's something totally 
> > different from actually stopping the _devices_.
> 
> Right. 
> 
> What you _do_ need to do, is stop the user-level actions.

Well, user-level actions are stopped because of refrigerator.

> Before you suspend, you need to make the machine quiescent, in other 
> words. The devices are still working, but you really really don't want to 
> do this while things are still _happening_.
> 
> Now, with suspend-to-RAM, I suspect we could even avoid that until the 
> very last phase (ie the actual suspend code). But quite frankly, from a 
> pure debuggability standpoint, I do think we want to basically try to make 
> everything as quiet as humanly possible.

Suspend-to-RAM theoretically does not need any kind of stopping, and
on ppc (IIRC) no stopping is really done. For suspend-to-disk, both
user actions (so that they do not write to disk after atomic copy is
done) and DMA (so that atomic image is not corrupted) needs to be
stopped.

> So think about what we do now: We special-case X, and we special-case the 
> save-to-disk device, and we special-case the console printouts, and we 
> special-case a lot of other things, AND WE STILL GOT IT WRONG. Try
> using 

Actually no, we are not special-casing the disk device. There was
discussion about doing that, but it is not going to happen.

X are special, because they are user-level hardware driver. If/when we
meet more user-level hardware drivers, we'll have to invent something
extensible.
								Pavel

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