On 11 September 2015 at 14:08, Mark Brown <broonie@xxxxxxxxxx> wrote: > On Mon, Sep 07, 2015 at 02:23:29PM +0200, Tomeu Vizoso wrote: >> Walks the OF tree up and finds the closest ancestor that has a struct >> device associated with it, probing it if isn't bound to a driver yet. > >> The above should ensure that the dependency represented by the passed OF >> node is available, because probing a device should cause its descendants >> to be probed as well (when they get registered). > > I'm still not seeing how this works for MFDs where the MFD binding is > present directly in DT. The same problem should happen with simple-bus nodes such as nvidia,tegra124-host1x in which children devices are represented in the DT (and registered right after their parent) and depend on their parent for their operation. Looked at why it wasn't being a problem in my tests and Thierry mentioned that tegra_host1x_driver takes care of the synchronization between the bus and their children. So children would make use of the bus only once it has finished probing and is ready to work (the init and exit callbacks in host1x_client_ops signal when the bus is safe to use). AFAICS, this is a must currently for correct operation in simple-bus and simple-mfd situations, because probing order is currently very unpredictable and it's totally possible for the probing of a child to start before the probing of its parent has finished (if async probing is enabled or if a module is loaded that registers a child's driver at the wrong time). I would prefer if the core would take care of making sure that parents are always probed before their children, but the unconditional locking of the parent device stands in the way. Regards, Tomeu -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
