Re: [PATCH RFC 1/2] of: property: fw_devlink: Follow GPIO nexus maps

[Bartosz Golaszewski <brgl@kernel.org>]

On Wed, 2 Sep 2026 15:22:36 +0200, Ernest Van Hoecke
<ernestvanhoecke@gmail.com> said:
> On Wed, Sep 02, 2026 at 05:30:19AM -0700, Bartosz Golaszewski wrote:
>> On Wed, 2 Sep 2026 13:41:39 +0200, Ernest Van Hoecke
>> <ernestvanhoecke@gmail.com> said:
>> > From: Ernest Van Hoecke <ernest.vanhoecke@toradex.com>
>> >
>> > GPIO consumers use of_parse_phandle_with_args_map() to resolve specifiers
>> > through gpio-map properties. fw_devlink instead parses GPIO properties as
>>
>> Unlike PWM, there's no such thing as "gpio-map" properties.
>>
> Hi Bartosz,
>
> bd6f2fd5a1d5 ("of: Support parsing phandle argument lists through a
> nexus node") added support for nexus nodes, and then c11e6f0f04db ("gpio:
> Support gpio nexus dt bindings") added support for "gpio-map".
>
> Herve later added support for pwm nexus dt bindings modeled on the GPIO
> support in e71e46a6f19c ("pwm: Add support for pwm nexus dt bindings").
>
> Please let me know if I misunderstood something.
>

No, sorry, it's me who didn't get that part correctly.

>> > direct phandle references, so it records the nexus node as the supplier
>> > rather than the mapped GPIO provider.
>> >
>>
>> Can you point me to an example? I'm not sure what a nexus node is in the
>> context of GPIO.
>
> Stephen gave an example usage in his commit message implementing
> of_parse_phandle_with_args_map():
> 	soc {
> 	        soc_gpio1: gpio-controller1 {
> 	                #gpio-cells = <2>;
> 	        };
>
> 	        soc_gpio2: gpio-controller2 {
> 	                #gpio-cells = <2>;
> 	        };
> 	};
>
> 	connector: connector {
> 	        #gpio-cells = <2>;
> 	        gpio-map = <0 0 &soc_gpio1 1 0>,
> 	                   <1 0 &soc_gpio2 4 0>,
> 	                   <2 0 &soc_gpio1 3 0>,
> 	                   <3 0 &soc_gpio2 2 0>;
> 	        gpio-map-mask = <0xf 0x0>;
>         	gpio-map-pass-thru = <0x0 0x1>
> 	};
>
> 	expansion_device {
>         	reset-gpios = <&connector 2 GPIO_ACTIVE_LOW>;
> 	};
>
> Admittedly, this hasn't seen much (any?) actual use in the device trees
> yet.
>
> We (Toradex) would like to use it to specify a LVDS connector on our
> boards. This connector appears on different carrier boards that all mate
> with the same display and have the same pinout. The only potential
> difference is which PWMs and GPIOs are connected to the connector.
>
> There, specifying the LVDS connector as a nexus node on the relevant
> carrier board DTS/DTSI would allow us to reuse the same display overlay.
> That example usage is given by Leonardo Costa here:
> https://lore.kernel.org/all/juuc4af7ndbajcl7gzf4tg5qz2q2j5tt3rvql4jbauradujrre@gc5nbdhhixaf/
> Note how we have the connector on imx8mp-verdin-dev.dtsi but could also
> add it to other boards, i.e: imx8mp-verdin-mallow.dtsi
>
> Note that in that example we used the "tdx,verdin-lvds-connector"
> compatible for the connector. Since this is a nexus node and just a
> dumb connector without driver, not having a compatible would make sense.
> In a final implementation we could specify a compatible + binding if
> that specifies the ABI better. It is not entirely clear to me what is
> preferred at the moment, but that is disconnected from this patch
> series.
>

In that case it makes sense I guess and good to see someone actually using it
eventually.

Bartosz