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    SubjectRe: [PATCH v3 0/4] Solve postboot supplier cleanup and optimize probe ordering
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    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].

    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

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    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
    a Linux Foundation Collaborative Project

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