Re: [PATCH 1/3] driver core: enable drivers to use deferred probe from init

Luis R. Rodriguez
2014-07-28T18:49:04Z

On Mon, Jul 28, 2014 at 06:30:29PM +0000, Yuval Mintz wrote:
> > On Mon, Jul 28, 2014 at 06:52:48PM +0200, Luis R. Rodriguez wrote:
> > > On Mon, Jul 28, 2014 at 03:46:32PM +0000, Yuval Mintz wrote:
> > > > Sorry for not being clear, but I didn't meant 'what guarantees that the device
> > > > will be added to the deferred probe', but rather what guarantees that the
> > > > deferred workqueue will be scheduled.
> > > >
> > > > To the best of my knowledge the deferring mechanism works only if one device
> > > > is dependent upon another, e.g., for Multi-function devices where one device
> > > > probe is dependent upon the others - which are soon-to-be probed.
> > >
> > > The workqueue will be kicked when driver_deferred_probe_trigger() gets
> > > poked, we do that in the late_initcall(deferred_probe_initcall), it
> > > also gets flushed there with a flush_workqueue(deferred_wq).
>
> > But come to think of it that will work well for devices already plugged in
> > so indeed I think that driver_deferred_probe_add() needs a check added
> > for for if (!driver_deferred_probe_enable) then we have to
> > driver_deferred_probe_trigger(). The driver_deferred_probe_enable is set
> > to false upon init, but later on late init it gets set to true so with
> > that check we'd only generate the trigger after late init call.
>
> > I can fold that in the v2.
>
> > Luis
>
> But what about modules being added after the init-calls? If they try try to use this
> mechanism, what guarantees they'll eventually get probed?

bus_probe_device --> device_attach() -->
__device_attach() --> driver_probe_device() -->
__driver_probe_device() --> driver_deferred_probe_add()

And with the new hunk I mentioned I'd add then we'd trigger the
workqueue if its after late init. The change is in v2 series.

Luis