On Fri, Oct 14, 2011 at 12:56 PM, David Daney <ddaney.cavm@xxxxxxxxx> wrote: > On 10/14/2011 10:20 AM, Grant Likely wrote: >> >> On Fri, Oct 14, 2011 at 10:33 AM, Alan Stern<stern@xxxxxxxxxxxxxxxxxxx> >> wrote: >>> >>> On Fri, 14 Oct 2011, Grant Likely wrote: >>> >>>>> How can a device acquire children before it has a driver? >>>> >>>> There are a few potential situations in embedded systems (or at least >>>> nothing currently prevents it) where platform setup code constructs a >>>> device hierarchy without the aid of device drivers, and it is still >>>> possible for a parent device to be attached to a driver. IIUC, SPARC >>>> creates an entire hierarchy of platform_devices from all the nodes in >>>> the OpenFirmware device tree, and any of those devices can be bound to >>>> a driver. I don't like that approach, but at the very least it needs >>>> to be guarded against. >>> >>> Do these devices ever require deferred probes? >> >> Yes, they very well might. However, I'm happy with the limitation >> that only leaf devices can take advantage of probe deferral. >> > > > I have: > > I2C-Bus-A > +--Mux-I2C (controlled by parent I2C-Bus-A) > +---I2C-Bus-1 > | +--GPIO-Expander-A > | > +---I2C-Bus-2 > +--GPIO-Expander-B > > These all have a parent/child relationship so no deferral is needed, so far > so good. > > > Then this: > > MDIO-Bus-A > +---Mux-MDIO (controlled by GPIO-Expander-A) > +---MDIO-Bus-1 > | > +---MDIO-Bus-2 > +---PHY-1 > | > +---PHY-2 > > In this case the driver for Mux-MDIO needs to be deferred until *both* > MDIO-Bus-A's driver *and* GPIO-Expander-B's driver are loaded. A perfect > use case for the patch. > > Would you consider Mux-MDIO to be a 'leaf device'? If not, then I have real > problems with 'the limitation that only leaf devices can take advantage of > probe deferral' leaf device **at the time of its driver probe**. :-) After the device has all of its dependencies met, it can freely add child devices. In your case, the child devices will get added by the Mux-MDIO device driver, so all is good. g. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
