Re: [GIT PULL] PM updates for 2.6.33

Rafael J. Wysocki
2009-12-07T20:46:42Z

On Monday 07 December 2009, Linus Torvalds wrote:
>
> On Mon, 7 Dec 2009, Rafael J. Wysocki wrote:
> >
> > > The advantage: untouched drivers don't change ANY SEMANTICS AT ALL.
> >
> > This also was true for my patchset.
>
> That's simply not trye.
>
> You set async_suspend on every single PCI driver. I object very heavily to
> it.

That was a mistake, I admit.

However, it was done in a separate patch that (1) was not necessary and (2)
shouldn't have been there. Sorry for making the mistake of including that into
the patchset. So I understand your objection to that and let's not get back to
this again, ok?

> You also introduce this whole big "callback when ready", and
> "non-topoligical PM dependency chain" thing. Which I also object to.

These things are also non-essential. Acutally they wasn't there in the initial
version of my patches and were added after people had complained that it had
not been parallel enough and hadn't take the off-tree dependecies into account.

I could remove these things either and quite easily.

> Notice how with the simpler "lock parent" model, you _can_ actually encode
> non-topological dependencies, but you do it by simply read-locking
> whatever other independent device you want. So if an architecture has some
> system devices that have odd rules, that architecture can simply encode
> those rules in its suspend() functions.

I'm not arguing against that. In fact, my only worry were that additional
suspend/resume callbacks I really wouldn't like to introduce. But since you've
found a way of doing things without them, I'm totally fine with this approach.

> It doesn't need to expose it to the device layer - because the device
> layer won't even care. The code will just automatically "do the right
> thing" without even having that notion of PM dependencies at any other
> level than the driver that knows about it.
>
> No registration, no callbacks, no nothing.
>
> > In my patchset the drivers didn't need to do all that stuff. The only thing
> > they needed, if they wanted their suspend/resume to be executed
> > asynchronously, was to set the async_suspend flag.
>
> In my patchset, the drivers don't need to either.
>
> The _only_ thing that would do this is something like the USB layer. We're
> talking ten lines of code or so. And you get rid of all the PM
> dependencies and all the infrastructure - because the model is so simple
> that it doesn't need any.

It just uses a different way of representing these things, perhaps more
efficiently.

> (Well, except for the infrastructure to run things asynchronously, but
> that was kind of my point from the very beginning: we can just re-use all
> that existing async infrastructure. We already have that).

So I guess the only thing we need at the core level is to call
async_synchronize_full() after every stage of suspend/resume, right?

Rafael