Re: [PATCH v2 2/8] dt-bindings: arm: apple: Add apple,pmgr binding

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On 27/10/2021 03.25, Rob Herring wrote:
On Mon, Oct 25, 2021 at 11:47:12PM +0900, Hector Martin wrote:
+  compatible:
+    items:
+      - enum:
+          - apple,t8103-pmgr
+          - apple,t8103-minipmgr
+      - const: apple,pmgr
+      - const: syscon
+      - const: simple-mfd


'simple-mfd' means 'there's nothing in this node that any of the child
nodes depend on'. You should be somewhat certain as dropping it later
creates compatibility issues.

Hmm, I see simple-mfd turns this into a bus which I guess allows child nodes to be probed without the parent node doing anything special (then we use syscon_node_to_regmap to get the syscon instantiated). Do you have a example use case for doing this without simple-mfd?

At this point I can't think of anything we'd need from the parent node, especially if we end up using this syscon strictly for pwrstate subnodes (which seems likely at this point). One thing that comes to mind is telling the PMP (a coprocessor in charge of power metrics/management) about some domains being turned on/off, which is apparently a thing, but that wouldn't even be in this node; that'd have to be a phandle property in the child nodes referencing a PMP/coprocessor node elsewhere (none of which is implemented right now, and which should be backwards compatible once it is).

If it turns out we do have a dep of some sort in the end, could we just have the child node driver return -EPROBE_DEFER until the parent is probed and has made whatever service available? That would allow us to keep simple-mfd, right?

If it works for you, I'll also just squash the two bindings into one commit for the next spin, since there is a direct dependency at this point and it should make things easier. Otherwise, I can just swap the order if you prefer it that way.

Ack on the other formatting changes; if the rest of the series looks good to the other folks I'll try to respin this into a v3 soon, to see if we can sneak it in by 5.16, since it'd be nice to have the power domain stuff in there :)

--
Hector Martin (marcan@xxxxxxxxx)
Public Key: https://mrcn.st/pub



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