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

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@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@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@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@konsulko.com

lib/libfdt/fdt_overlay.c | 148 ++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 147 insertions(+), 1 deletion(-)

Reviewed-by: Simon Glass sjg@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