Re: [PATCH 1/2] fdt: Allow stacked overlays phandle references

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Fri, Jul 14, 2017 at 10:21:01AM +0300, Pantelis Antoniou wrote:
> Hi Frank,
> 
> On Thu, 2017-07-13 at 14:40 -0700, Frank Rowand wrote:
> > On 07/13/17 14:22, Phil Elwell wrote:
> > > On 13/07/2017 21:07, Frank Rowand wrote:
> > >> On 07/13/17 12:38, Phil Elwell wrote:
> > >>
> 
> [snip]
> 
> > > hope an inability to solve the problem posed by this advanced usage won't
> > > prevent a solution to a simpler problem from being accepted.
> 
> I have waited until people started commenting on this patchset before
> replying.
> 
> I think we agree on a few things to keep the discussion moving forward.
> 
> 1. Stacked overlays are useful and make overlays easier to use.

Agreed.

> 2. Changing the overlay symbols format now would be unwise.

Agreed.  At least, I don't think updating the symbols alone would be
silly without revisiting everything in the overlay format and making
something completely new.

> 3. A number of extensions have been put forward/requested.
> 
> 3.1. There should be a method to place a symbol on a node that didn't
> have one originally (due to vendor supplying broken DTB or being
> generated by firmware at runtime).

There already is.  An overlay can update *anything* in the base tree,
including the /__symbols__ node.  Of course you need the exact path of
the node to tag in the base tree, but you were always going to need
that.

> 3.2. Scoping symbol visibility in case of clashes. This can the ability
> to put multiple path references to a single label/symbol. i.e.
> foo = "/path/bar", "/path/bar/baz";
> Resolving the ambiguity would require the caller to provide it's
> 'location' on the tree. I.e. a device under /path/bar/baz would resolve
> to the latter. It is a big change semantically.

I think this would be a nice idea, but trying to do it as a update to
the existing overlay format will be really difficult verging on
impossible.

Better to keep this in mind as a design goal for a new format to
replace overlays.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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