On Tue, Jul 2, 2019 at 5:03 PM David Collins <collinsd@xxxxxxxxxxxxxx> wrote: > > Hello Saravana, > > On 7/1/19 5:48 PM, Saravana Kannan wrote: > ... > > TODO: > > - For the case of consumer child sub-nodes being added by a parent > > device after late_initcall_sync we might be able to address that by > > recursively parsing all child nodes and adding all their suppliers as > > suppliers of the parent node too. The parent probe will add the > > children before its probe is completed and that will prevent the > > supplier's sync_state from being executed before the children are > > probed. > > > > But I'll write that part once I see how this series is received. > > I don't think that this scheme will work in all cases. It can also lead > to probing deadlock. > > Here is an example: > > Three DT devices (top level A with subnodes B and C): > /A > /A/B > /A/C > C is a consumer of B. > > When device A is created, a search of its subnodes will find the link from > C to B. Since device B hasn't been created yet, of_link_to_suppliers() > will fail and add A to the wait_for_suppliers list. This will cause the > probe of A to fail with -EPROBE_DEFER (thanks to the check in > device_links_check_suppliers()). As a result device B will not be created > and device A will never probe. > > You could try to resolve this situation by detecting the cycle and *not* > adding A to the wait_for_suppliers list. However, that would get us back > to the problem we had before. A would be allowed to probe which would > then result in devices being added for B and C. If the device for B is > added before C, then it would be allowed to immediately probe and > (assuming this all takes place after late_initcall_sync thanks to modules) > its sync_state() callback would be called since no consumer devices are > linked to B. > > Please note that to change this example from theoretical to practical, > replace "A" with apps_rsc, "B" with pmi8998-rpmh-regulators, and "C" with > pm8998-rpmh-regulators in [1]. Interesting use case. First, to clarify my TODO: I was initially thinking of the recursive "up-heritance" of suppliers from child to parent to handle cases where the supplier is a device from some other top level device (or its child). My thinking has evolved a bit on that. I think the parent needs to inherit only from it's immediate children and not its grandchildren (the child is responsible for handling grandchildren suppliers). I'll also have to make sure I don't try to create a link from a parent device to one of its child device nodes (should be easy to check). Anyway, going back to your case, for dependencies between child nodes of a parent, can't the parent just populate them in the right order? You can loop through the children and add them in multiple stages. I'll continue to think if I can come up with anything nicer on the drivers, but even if we can't come up with anything better, we can still make sync_state() work. Cheers, Saravana > > Take care, > David > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/qcom/sdm845-mtp.dts?h=v5.2-rc7#n55 > > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project
