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 > > bootgraph.pl > > 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... Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
