Quoting Pavan Kondeti (2022-06-20 01:54:15) > +Felipe, Bjorn > > On Thu, Jun 16, 2022 at 10:15:49AM -0700, Matthias Kaehlcke wrote: > > On Thu, Jun 16, 2022 at 02:41:10PM +0530, Pavan Kondeti wrote: > > > > Good point! It doesn't really ensure that the child is probed (actually it > > won't be probed and DL_FLAG_AUTOPROBE_CONSUMER doesn't make sense here), it > > could happen that dwc3_qcom_probe() is deferred multiple times, but eventually > > the PHYs should be ready and dwc3_probe() be invoked through > > of_platform_populate(). > > This is a generic problem i.e if a parent can only proceed after the child > devices are bounded (i.e probed successfully), how to ensure this behavior > from the parent's probe? Since we can't block the parent probe (async probe is > not the default behavior), we have to identify the condition that the children > are deferring probe, so that parent also can do that. > > Can we add a API in drivers core to tell if a device probe is deferred or > not? This can be done by testing list_empty(&dev->p->deferred_probe) under > deferred_probe_mutex mutex. The parent can return EPROBE_DEFER based on this > API return value. > > Another alternative would be explicitly checking if the child device suppliers > are ready or not before adding child device. That would require decoupling > of_platform_populate() to creating devices and adding devices. > > Note that this problem is not just limited to suppliers not ready. if the > dwc3-qcom is made asynchronous probe, then its child also probed > asynchronously and there is no guarantee that child would be probed by the > time of_platform_populate() is returned. The bus notifier might come handy > in this case. The parent can register for this notifier and waiting for > the children device's BUS_NOTIFY_BOUND_DRIVER/BUS_NOTIFY_DRIVER_NOT_BOUND > notifications. This would also work in our case, if we move to > of_platform_populate() outside the probe(). > > Would like to hear other people thoughts on this. > I'm not following very closely but it sounds like a problem that may be solved by using the component driver code (see include/linux/component.h). That would let you move anything that needs to be done once the child devices probe to the aggregate driver 'bind' function (see struct component_master_ops::bind).
