[PATCH v3 0/2] Add capability to append to property

[Ayush Singh <ayush@beagleboard.org>]

Allow appending values to a property instead of overriding the previous
values of property.

Currently, we have /delete-node/ and /delete-property/, but lack
/append-property/. Hence we end up having to repeat all existing values
when appending to a property (e.g. see [1] appending to clocks from
[2]).

This functionality is also important for creating a device tree based
implementation to support different types of addon-boards such as
mikroBUS, Grove [3], etc.

In practice, it looks as follows:

```
dts-v1/;

/ {
	str-prop = "0";
};

/ {
	/append-property/ str-prop = "1";
};
```

Open items
- Appending to non-existent property:

  I think it is better to create a new property if the property does not
  exist instead of giving an error.
  If the default is an error, then the condition, "create a property if
  it does not exist, else append" cannot be expressed. I think this
  behaviour is desirable with more complex overlays required for
  supporting addon boards using devicetree.

[3] https://lore.kernel.org/linux-arm-kernel/20240702164403.29067-1-afd@ti.com/
[2] https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/renesas/r8a77951-salvator-xs.dts#L39
[1] https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/renesas/r8a77951.dtsi#L3334

Signed-off-by: Ayush Singh <ayush@beagleboard.org>

---
Changes in v3:
- Add support for annotations. Works similar to nodes (since they
  already append by default).
- Link to v2: https://lore.kernel.org/r/20240830-append-v2-0-ec1e03f110ad@beagleboard.org

Changes in v2:
- Add comment for append struct member.
- Small code improvements
- Improve test
- Link to v1: https://lore.kernel.org/r/20240827-append-v1-0-d7a126ef1be3@beagleboard.org

---
Ayush Singh (2):
      dtc: Add /append-property/
      tests: Add test for append-property

 dtc-lexer.l           |  7 +++++++
 dtc-parser.y          |  6 ++++++
 dtc.h                 |  5 +++++
 livetree.c            | 36 +++++++++++++++++++++++++++++-------
 tests/append_prop.dts | 21 +++++++++++++++++++++
 tests/run_tests.sh    |  7 +++++++
 6 files changed, 75 insertions(+), 7 deletions(-)
---
base-commit: 99031e3a4a6e479466ae795790b44727434ca27d
change-id: 20240827-append-f614fe3261f9

Best regards,
-- 
Ayush Singh <ayush@beagleboard.org>