Boolean type properties are usually considered true if present and false
when they do not exist. This works well for many in-tree board dts and
existing drivers.
    
When users need to overrride boolean values from included dts,
/delete-property/ is recommend. This however does not work in overlays
(addons).

Geert pointed out [1] that there are several invitations for using
strings "true" and "false" on boolean properties: [1], [2], [3].

Add support for a string value "false" to be considered false on boolean
properties by changing of_property_read_bool implementation.

Affected by this issue is AM642 HummingBoard-T overlay to enable usb-3.1
function. This is an alternative solution to dropping
it's disfynctional overlay [1].

[1] https://lore.kernel.org/linux-devicetree/CAMuHMdWY0J7uooeRbUGwjkeCLd2UVyN9dtDWUkg5pJ3sAULdsQ@mail.gmail.com/
[2] Documentation/devicetree/bindings/sound/rt5651.txt
[3] Documentation/devicetree/bindings/sound/pcm3060.txt
[4] arch/arm/boot/dts/ti/omap/am335x-baltos.dtsi
[5] https://lore.kernel.org/linux-devicetree/20241101-am64-hb-fix-overlay-v1-1-080b98b057b6@solid-run.com/

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Closes: https://lore.kernel.org/linux-devicetree/CAMuHMdXTgpTnJ9U7egC2XjFXXNZ5uiY1O+WxNd6LPJW5Rs5KTw@mail.gmail.com
Fixes: bbef42084cc1 ("arm64: dts: ti: hummingboard-t: add overlays for m.2 pci-e and usb-3")
Signed-off-by: Josua Mayer <josua@solid-run.com>

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jon Nettleton <jon@solid-run.com>
Cc: Yazan Shhady <yazan.shhady@solid-run.com>
Cc: rabeeh@solid-run.com

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
Josua Mayer (2):
      of: add support for value "false" to of_property_read_bool
      arm64: dts: ti: k3-am642-hummingboard-t-usb3: fix overlay boolean value

 arch/arm64/boot/dts/ti/k3-am642-hummingboard-t-usb3.dtso |  2 +-
 drivers/of/property.c                                    |  2 +-
 include/linux/of.h                                       | 13 ++++++++-----
 3 files changed, 10 insertions(+), 7 deletions(-)
---
base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
change-id: 20241112-am64-overlay-bool-60a35da933f7

Best regards,
-- 
Josua Mayer <josua@solid-run.com>

On Tue, Nov 12, 2024 at 12:41 AM Josua Mayer <josua@solid-run.com> wrote:
>
> Boolean type properties are usually considered true if present and false
> when they do not exist. This works well for many in-tree board dts and
> existing drivers.
>
> When users need to overrride boolean values from included dts,
> /delete-property/ is recommend. This however does not work in overlays
> (addons).

As soon as someone needs to delete a non-boolean property, we're back
to the same problem. If you want to fix it, you need to fix it for any
property.


> Geert pointed out [1] that there are several invitations for using
> strings "true" and "false" on boolean properties: [1], [2], [3].

There's always bad examples...

> Add support for a string value "false" to be considered false on boolean
> properties by changing of_property_read_bool implementation.

Any existing s/w will treat 'foo = "false"' as true. It's an ABI.

Rob