On Mon, May 16, 2016 at 3:18 PM, Pantelis Antoniou <pantelis.anton...@konsulko.com> wrote: > Add a description of the target root overlay method to the overlay > documention file. > > Signed-off-by: Pantelis Antoniou <pantelis.anton...@konsulko.com> > --- > Documentation/devicetree/overlay-notes.txt | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/Documentation/devicetree/overlay-notes.txt > b/Documentation/devicetree/overlay-notes.txt > index 6995fc1..3e8df30 100644 > --- a/Documentation/devicetree/overlay-notes.txt > +++ b/Documentation/devicetree/overlay-notes.txt > @@ -104,6 +104,10 @@ If your board has multiple slots/places where a single > overlay can work > and each slot is defined by a node, you can use the > of_overlay_create_target_index() method to select the target. > > +For overlays on probeable busses, use the of_overlay_create_target_root() > method > +in which you supply a device node as a target root, and which all target > +references in the overlay are performed relative to that node.
This needs a better explanation and an example. "Applying overlays to multiple places for probeable busses" is not sufficient. Describe what is the problem/flow, and then how does the implementation work. I don't think this problem is limited to probeable busses either. Not knowing the target to apply the overlay to is the same problem for connectors with non-probeable signals. I find a couple of things problematic with the implementation. There's no way to validate that an overlay should apply to a base node. If users just always make the target "/", then any overlay can apply to any location the nodes could apply anywhere. It requires a kernel change for every location you want to apply the overlay to. Maybe I don't understand the usecase. I feel like we are creating too many syntax's to apply overlays. I get that there are different usecases, but that doesn't necessarily mean the syntax needs to be different. > + > Overlay DTS Format > ------------------ > > @@ -141,3 +145,7 @@ contains the information required to map from a phandle > to a tree location. > Using a target index requires the use of a selector target on the call to > of_overlay_create_target_index(). I.e. passing an index of 0 will select the > target in the foo node, an index of 1 the bar node, etc. > + > +Note that when using the target root create method all target references must > +lie under the target root node. I.e. the overlay is not allowed to 'break' > out > +of the root. That is not enforceable though, right? Rob
