[U-Boot] [PATCH 3/5] fdt: Allow stacked overlays phandle references

[Pantelis Antoniou]

Hi Simon,

On Thu, 2017-07-06 at 21:58 -0600, Simon Glass wrote:
> On 30 June 2017 at 10:23, Pantelis Antoniou
> <pantelis.antoniou at konsulko.com> wrote:
> > This patch enables an overlay to refer to a previous overlay's
> > labels by performing a merge of symbol information at application
> > time.
> >
> > In a nutshell it allows an overlay to refer to a symbol that a previous
> > overlay has defined. It requires both the base and all the overlays
> > to be compiled with the -@ command line switch so that symbol
> > information is included.
> >
> > base.dts
> > --------
> >
> >         /dts-v1/;
> >         / {
> >                 foo: foonode {
> >                         foo-property;
> >                 };
> >         };
> >
> >         $ dtc -@ -I dts -O dtb -o base.dtb base.dts
> >
> > bar.dts
> > -------
> >
> >         /dts-v1/;
> >         /plugin/;
> >         / {
> >                 fragment at 1 {
> >                         target = <&foo>;
> >                         __overlay__ {
> >                                 overlay-1-property;
> >                                 bar: barnode {
> >                                         bar-property;
> >                                 };
> >                         };
> >                 };
> >         };
> >
> >         $ dtc -@ -I dts -O dtb -o bar.dtb bar.dts
> >
> > baz.dts
> > -------
> >
> >         /dts-v1/;
> >         /plugin/;
> >         / {
> >                 fragment at 1 {
> >                         target = <&bar>;
> >                         __overlay__ {
> >                                 overlay-2-property;
> >                                 baz: baznode {
> >                                         baz-property;
> >                                 };
> >                         };
> >                 };
> >         };
> >
> >         $ dtc -@ -I dts -O dtb -o baz.dtb baz.dts
> >
> > Applying the overlays:
> >
> >         $ fdtoverlay -i base.dtb -o target.dtb bar.dtb baz.dtb
> >
> > Dumping:
> >
> >         $ fdtdump target.dtb
> >         / {
> >             foonode {
> >                 overlay-1-property;
> >                 foo-property;
> >                 linux,phandle = <0x00000001>;
> >                 phandle = <0x00000001>;
> >                 barnode {
> >                     overlay-2-property;
> >                     phandle = <0x00000002>;
> >                     linux,phandle = <0x00000002>;
> >                     bar-property;
> >                     baznode {
> >                         phandle = <0x00000003>;
> >                         linux,phandle = <0x00000003>;
> >                         baz-property;
> >                     };
> >                 };
> >             };
> >             __symbols__ {
> >                 baz = "/foonode/barnode/baznode";
> >                 bar = "/foonode/barnode";
> >                 foo = "/foonode";
> >             };
> >         };
> >
> > Signed-off-by: Pantelis Antoniou <pantelis.antoniou at konsulko.com>
> > ---
> >  lib/libfdt/fdt_overlay.c | 148 ++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 147 insertions(+), 1 deletion(-)
> 
> Reviewed-by: Simon Glass <sjg at chromium.org>
> 
> I suppose that the upstream version has tests?
> 

Yes, and I could use a couple reviewers in the dtc mailing list.
 
> Does it make sense to implement this in the live tree instead, or do
> you need to modify the DT before relocation?
> 

There is a port of a patch that works on the live tree; I guess I can
port it to u-boot's live tree as well.

Speaking of which I've done quite a bit of work on a different live tree
implementation as well. I would propose we split off u-boot's one in a
library and port my changes there. That way we can have a definitive
live tree implementation, and in the future move dtc's internal live
tree to it as well. We keep on implementing the same functionality in
different flavors for years, let's consolidate, and start working on
ideas for the future.

> - Simon

Regards

-- Pantelis