Date: Thu, 25 Nov 2004 19:53:04 +0100
From: Pavel Machek <pavel@ucw.cz>
To: kernel list <linux-kernel@vger.kernel.org>,
       Nigel Cunningham <ncunningham@linuxmail.org>
Subject: Re: Suspend2 merge: 1/51: Device trees
Message-ID: <20041125185304.GA1260@elf.ucw.cz>
References: <20041125165413.GB476@openzaurus.ucw.cz>
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Hi!

> This patch allows the device tree to be split up into multiple trees. I
> don't really expect it to be merged, but it is an important part of
> suspend at the moment, and I certainly want to see something like it
> that will allow us to suspend some parts of the device tree and not
> others. Suspend2 uses it to keep alive the hard drive (or equivalent)
> that we're writing the image to while suspending other devices, thus
> improving the consistency of the image written.
> 
> I remember from last time this was posted that someone commented on
> exporting the default device tree; I haven't changed that yet.

Q: I do not understand why you have such strong objections to idea of
selective suspend.

A: Do selective suspend during runtime power managment, that's
okay. But
its useless for suspend-to-disk. (And I do not see how you could use
it for suspend-to-ram, I hope you do not want that).

Lets see, so you suggest to

* SUSPEND all but swap device and parents
* Snapshot
* Write image to disk
* SUSPEND swap device and parents
* Powerdown

Oh no, that does not work, if swap device or its parents uses DMA,
you've corrupted data. You'd have to do

* SUSPEND all but swap device and parents
* FREEZE swap device and parents
* Snapshot
* UNFREEZE swap device and parents
* Write
* SUSPEND swap device and parents

Which means that you still need that FREEZE state, and you get more
complicated code. (And I have not yet introduce details like system
devices).

								Pavel
-- 
People were complaining that M$ turns users into beta-testers...
...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl!
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