Broken bitbang 1-wire on Amlogic after kernel update

[Nikita Maslo]

Hi,

I was running linux-6.12.67 on a hardkernel odroid-c2 (Amlogic S905) Amlogic board with DS18B20 on
w1-gpio (1-Wire bitbang), everything worked fine. After updating the
kernel, 1-wire stopped working the DS18B20 fails to enumerate or
reads back the broken-bus, and dmesg
gets flooded with WARNINGs from gpiod_set_value/gpiod_get_value
called from w1_gpio_write_bit/w1_gpio_read_bit.

Hardware: Hardkernel ODROID-C2 (Amlogic S905).
Kernel:   linux-6.18.15 (also reproduces on linux-6.12.69; last
          known-good for me was linux-6.12.67).

Device tree fragment used:

    / {
        onewire {
            compatible = "w1-gpio";
            gpios = <&gpio GPIOX_17 GPIO_ACTIVE_HIGH>;
        };
    };

dmesg, captured on ODROID-C2 / linux-6.18.15:

  [   59.102855] ------------[ cut here ]------------
  [   59.102891] WARNING: CPU: 0 PID: 1145 at drivers/gpio/gpiolib.c:3880 gpiod_set_value+0x78/0x88
  [   59.103569] CPU: 0 UID: 0 PID: 1145 Comm: w1_bus_master1 Tainted: G        WC          6.18.15-current-meson64 #8 PREEMPT
  [   59.103618] Hardware name: Hardkernel ODROID-C2 (DT)
  [   59.103658] pc : gpiod_set_value+0x78/0x88
  [   59.103687] lr : w1_gpio_write_bit+0x20/0x38 [w1_gpio]
  [   59.104161] Call trace:
  [   59.104175]  gpiod_set_value+0x78/0x88 (P)
  [   59.104210]  w1_gpio_write_bit+0x20/0x38 [w1_gpio]
  [   59.104238]  w1_reset_bus+0x84/0xe0 [wire]
  [   59.104272]  w1_search+0x88/0x2a0 [wire]
  [   59.104304]  w1_search_devices+0x54/0x90 [wire]
  [   59.104336]  w1_search_process_cb+0x84/0x170 [wire]
  [   59.104368]  w1_process+0x1c0/0x238 [wire]
  [   59.104400]  kthread+0x14c/0x218
  [   59.104432]  ret_from_fork+0x10/0x20
  [   59.104464] ---[ end trace 0000000000000000 ]---

A symmetric WARN at gpiolib.c:3501 fires from gpiod_get_value via
w1_gpio_read_bit on every read slot.

After a little researching, the suspect commit looks like:

28f240683871 ("pinctrl: meson: mark the GPIO controller as sleeping")

I also tested bitbang i2c-gpio on the same hardware after the update,
it seems to keep working.