AW: AW: [PATCH 1/2] dt-bindings: i2c: Add i2c-shared-gpio

[<markus.stockhausen@gmx.de>]

> Von: Wolfram Sang <wsa+renesas@sang-engineering.com> 
> Gesendet: Samstag, 9. Mai 2026 19:39
> An: markus.stockhausen@gmx.de; Bartosz Golaszewski <brgl@kernel.org>
> Cc: 'Rob Herring' <robh@kernel.org>; andi.shyti@kernel.org;
linux-i2c@vger.kernel.org
> Betreff: Re: AW: [PATCH 1/2] dt-bindings: i2c: Add i2c-shared-gpio
>...
>
> Now, the GPIO subsystem since recently allows for shared GPIOs[1]. This
> sounds like the proper approach to me. Sadly, I can't help much because
> I have not used this API so far. So, it seems you rather need a GPIO
> expert... CCing Bart.
>
> @Bart: is it possible to share a GPIO so that multiple i2c-gpio
> instances can use the same GPIO as SCL? Use case is explained in the
> cover letter[2].

Thanks fort he hint. That looks partly promising. I gave this a quick try 
on Kernel 6.18 in OpenWrt. Set the target to HAVE_SHARED_GPIOS. 
Finally added several backports (deadlock stalled the boot). Now it at 
least starts.

This dts:

	i2c0: i2c-sfp0 {
                compatible = "i2c-gpio";
                #address-cells = <1>;
                #size-cells = <0>;

                scl-gpios = <&gpio1 31 (GPIO_ACTIVE_HIGH |
GPIO_OPEN_DRAIN)>;
                sda-gpios = <&gpio1 6 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
	};

	i2c1: i2c-sfp1 {
                compatible = "i2c-gpio";
                #address-cells = <1>;
                #size-cells = <0>;

                scl-gpios = <&gpio1 31 (GPIO_ACTIVE_HIGH |
GPIO_OPEN_DRAIN)>;
                sda-gpios = <&gpio1 7 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
	};

Gives these messages:

[    2.048352] i2c-gpio i2c-sfp0: Slow GPIO pins might wreak havoc into
I2C/SMBus bus timing
[    2.058333] i2c-gpio i2c-sfp0: using lines 542 (SDA) and 573 (SCL)
[    2.066139] i2c-gpio i2c-sfp1: Slow GPIO pins might wreak havoc into
I2C/SMBus bus timing
[    2.076333] i2c-gpio i2c-sfp1: using lines 543 (SDA) and 574 (SCL)
[    2.084817] sfp sfp-p9: Host maximum power 1.0W
[    2.091419] sfp sfp-p10: Host maximum power 1.0W
[    2.200954] In rtldsa_vlan_setup
[    2.397223] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.407907] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.418605] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.429275] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.439937] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.450584] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.461223] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.471875] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1
[    2.482539] gpio-574 (scl): gpio_set_open_drain_value_commit: Error in
set_value for open drain err -1

I assume I must dig deeper here.

Markus