[PATCH 0/2] Register virtual GPIO keys for VNC

[marlonwu@126.com]

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From: Menglong Wu <marlonwu@126.com>

Test platform
-------------
Kernel: 4.14.98
Rootfs: BusyBox 1.29
QT: 4.7
x11vnc: 0.9.16

Purpose
-------------

To emulate a full ANSI keyboard on embedded devices without physical 
keyboards.
The server responds to key events via x11vnc.
This resolves the limitation where embedded systems only register a few 
GPIO keys, making them unable to process full keyboard inputs.

documented in Documentation/devicetree/bindings/input/vnc-virtual-input.yaml

Scenario
-------------

- /dev/input/event1: Physical GPIO buttons

- /dev/input/event2: Physical touchscreen

Assume my-pcb.dts defines two GPIO-based hardware keys (A and B).
When the VNC server x11vnc is started, a remote PC connects via a VNC 
client and attempts to send key inputs.
Since the Linux kernel only recognizes two keys, the UI on the embedded 
device only responds to ‘A’ and ‘B’.

Start x11vnc server:

```
    x11vnc -noipv6 -rawfb /dev/fb0 -forever -clip 640x480+0+0 \
      -pipeinput UINPUT:touch,tslib_cal=/etc/pointercal,\
      direct_key=/dev/input/event1,\
      direct_abs=/dev/input/event2
```

Monitor key events:

```
    hexdump /dev/input/event1
```

Original my-pcb.dts:


```
    gpio_keys {
        compatible = "gpio-keys";
        pinctrl-0 = <&pinctrl_gpio_keys>;

        key-a {
            label = "btn-key-a";
            gpios = <&gpio1 10 GPIO_ACTIVE_HIGH>;
            linux,code = <KEY_A>;
        };
        key-b {
            label = "btn-key-b";
            gpios = <&gpio1 11 GPIO_ACTIVE_HIGH>;
            linux,code = <KEY_A>;
        };
    };
```


Solution
-------------

Modify my-pcb.dts to support a virtual ANSI keyboard:

```
    #include "vnc-virtual-input.dtsi"

    // Originally, the DTS relied on physical GPIO keys
    gpio_keys {
        // Disable the original physical key node
        status = "disable";
    };

    // The virtual GPIO DTS node now integrates physical GPIO
    vnc_key {
        compatible = "gpio-keys";
        pinctrl-0 = <&pinctrl_gpio_keys>;
        
        key-a {
            label = "btn-key-a";
            gpios = <&gpio1 10 GPIO_ACTIVE_HIGH>;
            linux,code = <KEY_A>;
        };
        key-b {
            label = "btn-key-b";
            gpios = <&gpio1 11 GPIO_ACTIVE_HIGH>;
            linux,code = <KEY_A>;
        };
    }
```
Menglong Wu (2):
  dt-bindings vnc virtual input
  ARM: dts: Add virtual GPIO input for VNC keyboard

 .../bindings/input/vnc-virtual-input.txt      | 153 +++++
 .../bindings/input/vnc-virtual-input.yaml     |  86 +++
 MAINTAINERS                                   |   8 +
 arch/arm/boot/dts/vnc-virtual-input.dtsi      | 569 ++++++++++++++++++
 4 files changed, 816 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/input/vnc-virtual-input.txt
 create mode 100644 Documentation/devicetree/bindings/input/vnc-virtual-input.yaml
 create mode 100644 arch/arm/boot/dts/vnc-virtual-input.dtsi

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