[PATCH] arm64: dts: mediatek: mt8188-geralt: enable touchpad

[Chen-Yu Tsai]

On Mon, May 4, 2026 at 3:28 PM Icenowy Zheng <zhengxingda at iscas.ac.cn> wrote:
>
> Despite the Ciri device's touchpad is on the detachable keyboard, the
> I2C HID device seen by Linux is emulated by ChromeOS EC and always
> present regardless of the presence of physical touchpad.

AFAIK it is actually an I2C HID device on the detachable keyboard.
The I2C bus is "tunneled" across the EC-EC connection. And if you
detach the keyboard, the I2C device will stop responding.

We have some downstream trickery to deal with this:

    https://crrev.com/c/6040044
    https://crrev.com/c/6040045

It basically involves registering the I2C device when the keyboard is
attached, and removing it when it is detached. We haven't gotten around
to upstreaming it though. I talked to Krzysztof about this design last
year, and I believe it was at least acceptable from DT point of view.

So this patch is somewhat incorrect, in that the trackpad should be
disabled by default, and its status should be toggled at runtime based
on the detachable keyboard events.

Otherwise if you boot the system without the keyboard, the driver will
probably fail to read the HID descriptor.


ChenYu

> Enable the device in the device tree.
>
> Signed-off-by: Icenowy Zheng <zhengxingda at iscas.ac.cn>
> ---
>  .../boot/dts/mediatek/mt8188-geralt.dtsi      | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/arch/arm64/boot/dts/mediatek/mt8188-geralt.dtsi b/arch/arm64/boot/dts/mediatek/mt8188-geralt.dtsi
> index 8e423504ec052..8f801454bf84c 100644
> --- a/arch/arm64/boot/dts/mediatek/mt8188-geralt.dtsi
> +++ b/arch/arm64/boot/dts/mediatek/mt8188-geralt.dtsi
> @@ -460,6 +460,18 @@ &i2c4 {
>         pinctrl-0 = <&i2c4_pins>;
>         clock-frequency = <400000>;
>         status = "okay";
> +
> +       /* The touchpad HID device is emulated by EC so it's always present */
> +       touchpad: touchpad at 56 {
> +               compatible = "hid-over-i2c";
> +               reg = <0x56>;
> +               hid-descr-addr = <0x0001>;
> +               interrupt-parent = <&pio>;
> +               interrupts = <148 IRQ_TYPE_LEVEL_LOW>;
> +               pinctrl-names = "default";
> +               pinctrl-0 = <&touchpad_int>;
> +               wakeup-source;
> +       };
>  };
>
>  &i2c5 {
> @@ -1131,6 +1143,14 @@ pins-bus {
>                 };
>         };
>
> +       touchpad_int: touchpad-int-pins {
> +               pins-ec-ap-touchpad-int-odl {
> +                       pinmux = <PINMUX_GPIO148__FUNC_B_GPIO148>;
> +                       input-enable;
> +                       bias-disable;
> +               };
> +       };
> +
>         uart0_pins: uart0-pins {
>                 pins-bus {
>                         pinmux = <PINMUX_GPIO31__FUNC_O_UTXD0>,
> --
> 2.52.0
>
>