Implement button push using servo motors controlled via pwm (#55)

1. Add to /boot/config.txt
```
dtoverlay=pwm
```

2. Create /etc/udev/rules.d/99-kvmd-pwm.rules
```
SUBSYSTEM=="pwm*", ACTION=="add", RUN+="/bin/chgrp -R kvmd /sys%p", RUN+="/bin/chmod -R g=u /sys%p"
SUBSYSTEM=="pwm*", ACTION=="change", ENV{TRIGGER}!="none", RUN+="/bin/chgrp -R kvmd /sys%p", RUN+="/bin/chmod -R g=u /sys%p"
```

3. Connect Servo motor like SG90 PWM connection to RPi GPIO18, +5V and GND to a 5V and GND pin on header

4. Add to /etc/kvmd/override.yaml
```
kvmd:
    gpio:
        drivers:
            servo1:
                type: pwm
                pwm_chip: 0                  # PWM Chip Number
                pwm_period: 20000000         # Servo Motor SG90 Period in nano-seconds
                duty_cycle_push: 1500000     # Servo Motor SG90 duty_cycle for pushing button
                duty_cycle_release: 1000000  # Servo Motor SG90 duty_cycle for releasing button
        scheme:
            short_press:
                driver: servo1
                pin: 0                       # Pin number is the PWM channel number on the PWM Chip
                mode: output
                switch: false
                pulse:
                    delay: 0.5
                    max_delay: 2
            long_press:
                driver: servo1
                pin: 0                       # Pin number is the PWM channel number on the PWM Chip
                mode: output
                switch: false
                pulse:
                    delay: 2
                    max_delay: 2
            extra_long_press:
                driver: servo1
                pin: 0                       # Pin number is the PWM channel number on the PWM Chip
                mode: output
                switch: false
                pulse:
                    delay: 10
                    max_delay: 20
        view:
            header:
                title: Controls
            table:
                - ["#Servo - Short Press", "short_press|Press"]
                - ["#Servo - Long Press", "long_press|Press"]
                - ["#Servo - Extra Long Press", "extra_long_press|Press"]
```

1 files changed, 126 insertions, 0 deletions

diff --git a/kvmd/plugins/ugpio/pwm.py b/kvmd/plugins/ugpio/pwm.py
new file mode 100644
index 00000000..90e7a50d
--- /dev/null
+++ b/kvmd/plugins/ugpio/pwm.py
@@ -0,0 +1,126 @@
+# ========================================================================== #
+#                                                                            #
+#    KVMD - The main Pi-KVM daemon.                                          #
+#                                                                            #
+#    Copyright (C) 2018-2021  Maxim Devaev <[email protected]>               #
+#                             Shantur Rathore <[email protected]>                #
+#                                                                            #
+#    This program is free software: you can redistribute it and/or modify    #
+#    it under the terms of the GNU General Public License as published by    #
+#    the Free Software Foundation, either version 3 of the License, or       #
+#    (at your option) any later version.                                     #
+#                                                                            #
+#    This program is distributed in the hope that it will be useful,         #
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of          #
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           #
+#    GNU General Public License for more details.                            #
+#                                                                            #
+#    You should have received a copy of the GNU General Public License       #
+#    along with this program.  If not, see <https://www.gnu.org/licenses/>.  #
+#                                                                            #
+# ========================================================================== #
+
+from periphery import PWM
+
+from typing import Dict
+from typing import Optional
+from typing import Set
+
+from ...logging import get_logger
+
+from ... import tools
+from ... import aiotools
+
+from ...yamlconf import Option
+
+from ...validators.basic import valid_int_f0
+
+from . import GpioDriverOfflineError
+from . import UserGpioModes
+from . import BaseUserGpioDriver
+
+
+# =====
+class Plugin(BaseUserGpioDriver):
+
+    def __init__(  # pylint: disable=super-init-not-called
+        self,
+        instance_name: str,
+        notifier: aiotools.AioNotifier,
+
+        pwm_chip: int,
+        pwm_period: int,
+        duty_cycle_push: int,
+        duty_cycle_release: int,
+    ) -> None:
+
+        super().__init__(instance_name, notifier)
+
+        self.__pwm_chip = pwm_chip
+        self.__pwm_period = pwm_period
+        self.__duty_cycle_push = duty_cycle_push
+        self.__duty_cycle_release = duty_cycle_release
+
+        self.__channels: Dict[int, Optional[bool]] = {}
+
+        self.__channel_pwm: Dict[int, PWM] = {}
+
+    @classmethod
+    def get_plugin_options(cls) -> Dict:
+        return {
+            "pwm_chip": Option(0, type=valid_int_f0),
+            "pwm_period": Option(20000000, type=valid_int_f0),
+            "duty_cycle_push": Option(1500000, type=valid_int_f0),
+            "duty_cycle_release": Option(1000000, type=valid_int_f0),
+        }
+
+    @classmethod
+    def get_modes(cls) -> Set[str]:
+        return set([UserGpioModes.OUTPUT])
+
+    def register_input(self, pin: int, debounce: float) -> None:
+        raise RuntimeError(f"Unsupported mode 'input' for pin={pin} on {self}")
+
+    def register_output(self, pin: int, initial: Optional[bool]) -> None:
+        self.__channels[pin] = initial
+
+    def prepare(self) -> None:
+        logger = get_logger(0)
+
+        for (pin, initial) in self.__channels.items():
+            try:
+                logger.info("Probing pwm chip %d channel %d ...", self.__pwm_chip, pin)
+                pwm = PWM(self.__pwm_chip, pin)
+                self.__channel_pwm[pin] = pwm
+                pwm.period_ns = self.__pwm_period
+                pwm.duty_cycle_ns = self.__duty_cycle_push if initial else self.__duty_cycle_release
+                pwm.enable()
+
+            except Exception as err:
+                logger.error("Can't get pwm chip %d channel %d: %s",
+                             self.__pwm_chip, pin, tools.efmt(err))
+
+    async def run(self) -> None:
+        await aiotools.wait_infinite()
+
+    async def cleanup(self) -> None:
+        for (pin, _) in self.__channels.items():
+            self.__channel_pwm[pin].disable()
+            self.__channel_pwm[pin].close()
+
+    async def read(self, pin: int) -> bool:
+        try:
+            return self.__channel_pwm[pin].duty_cycle_ns == self.__duty_cycle_push
+        except Exception:
+            raise GpioDriverOfflineError(self)
+
+    async def write(self, pin: int, state: bool) -> None:
+        try:
+            self.__channel_pwm[pin].duty_cycle_ns = self.__duty_cycle_push if state else self.__duty_cycle_release
+        except Exception:
+            raise GpioDriverOfflineError(self)
+
+    def __str__(self) -> str:
+        return f"PWM({self._instance_name})"
+
+    __repr__ = __str__