Re: [RFC v1 0/3] driver-core: add asynch module loading support

From: Dmitry Torokhov
Date: Sun Aug 31 2014 - 16:14:16 EST

On Sun, Aug 31, 2014 at 12:31:40PM -0700, Greg KH wrote:
> On Sun, Aug 31, 2014 at 12:24:46PM -0700, Arjan van de Ven wrote:
> > >>before we added the current async approach the approach of async init calls was tried
> > >>At the time, Linus hated it and he was right, it was not the right thing.
> > >>
> > >>What is different this time to make this the right thing to do ?
> > >
> > >Because otherwise drivers still have to do this, but open code it. Let's say I
> > >have a long operations (i.e. for some touchpads it takes about 2 secs to reset
> > >and configure it). I can offload that part into async_schedule() so it does not
> > >stop initialization of the rest of the system (why would I want to delay
> > >initializing of USB or storage system until touchpad is ready?) but if that
> > >initialization fails we end up with partially bound driver and device that is
> > >not really operable. I would very much prefer async and sync cases be the same
> > >- if probe() fails the driver is not bound to the device.
> > >
> > >I think it is wrong to make async probing system-wide, but driver opt-in shoudl
> > >be fine and right thing to do.
> > >
> >
> > I am completely fine if we make basically an async wrapper for
> > pci_register_driver() and friends.. that would be convenient I suppose.
> >
> > (but then again, in reality very few drivers take real time to init... most already
> > do the heavy work in open(). Not all can, sure, but if you look at a
> > graph of a typical boot it's only a few that matter).

Input devices normally can't as we need to publish their capabilities before
users start opening them.

> > And many drivers need to register with a subsystem, and there's some ordering around that,
> > and that's why we ended up with the async cookie stuff, so that you can do the
> > heavy work in parallel, but order near the end at registeration-with-the-subsystem time.
> >
> > But doing this on an initcall level was wrong back then, and I have yet to hear
> > a reason why it would be right this time.
> It's still wrong, it's not what I was thinking about when talking this
> over with Luis and Dmitry, I think something got lost in the
> translation...

Right, all (well almost all) I wanted is for individual drivers to declare
their probe() functions asynchronous and driver core scheduling async attach
and properly handle failures from it.

As I mentioned, resume has similar issues...


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