[PATCH v4 19/21] drivers/of: Support adding sub-tree

[Grant Likely]

On Mon, Jun 8, 2015 at 9:57 PM, Benjamin Herrenschmidt
<benh at kernel.crashing.org> wrote:
> On Sun, 2015-06-07 at 08:54 +0100, Grant Likely wrote:
>> > IE. conceptually, what overlays do today is quite rooted around the idea
>> > of having a fixed "base" DT and some pre-compiled DTB overlays that
>> > get added/removed. The design completely ignore the idea of a FW that
>> > maintains a "live" tree which we want to keep in sync, which is what we
>> > want to do here, or what we could do with a "live" open firmware
>> > implementation.
>>
>> Right, which is exactly the reason for the changeset/overlay split.
>> Overlays assume a fixed base, and that overlays are kind of like plug-in
>> modules. changeset makes no such assumption.
>
> So you suggest we create a function that takes an fdt and an "anchor" as input,
> and expands that FDT below that anchor, but does so by using the changeset API
> under the hood ?
>
> Even that looks somewhat tricky (turn that bit of FDT into a pile of changeset
> actions), however, I can see how we could create a new function inside changeset
> to attach a subtree.
>
> Ie. of_attach_subtree() (which could have it's own reconfig action but we
> don't care that much yet), which takes an expanded subtree and an anchor, and
> calls of_attach_node() in effect for all nodes in there.
>
> We could then have a two pass mechanism in our hotplug code:
>
>  - Expand the bit of fdt into a separate tree
>  - Use of_attach_subtree to "add" that subtree to the main tree
>
> What do you think ?

I like that.

g.