Messages in this thread | | | Date | Fri, 14 Oct 2011 12:09:00 -0700 | From | David Daney <> | Subject | Re: [PATCH 2/5] drivercore: Add driver probe deferral mechanism |
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On 10/14/2011 12:03 PM, Grant Likely wrote: > On Fri, Oct 14, 2011 at 12:56 PM, David Daney<ddaney.cavm@gmail.com> wrote: >> On 10/14/2011 10:20 AM, Grant Likely wrote: >>> >>> On Fri, Oct 14, 2011 at 10:33 AM, Alan Stern<stern@rowland.harvard.edu> >>> 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. >
Indeed. Thanks for the confirmation.
David Daney
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