Input: add support for the FlySky FS-iA6B RC receiver

This patch adds support for the FlySky FS-iA6B RC receiver (serial IBUS).

It allows the usage of the FlySky FS-i6 and other AFHDS compliant remote
controls as a joystick input device.

To use it, a patch to inputattach which adds the FS-iA6B as a 115200 baud
serial device is required. I will upstream it after this patch is merged.

More information about the hardware can be found here:

https://notsyncing.net/?p=blog&b=2018.linux-fsia6b

Signed-off-by: Markus Koch <markus@notsyncing.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

MAINTAINERS

@@ -12394,6 +12394,12 @@ S:	Maintained
 F:	Documentation/input/devices/pxrc.rst
 F:	drivers/input/joystick/pxrc.c
 
+FLYSKY FSIA6B RC RECEIVER
+M:	Markus Koch <markus@notsyncing.net>
+L:	linux-input@vger.kernel.org
+S:	Maintained
+F:	drivers/input/joystick/fsia6b.c
+
 PHONET PROTOCOL
 M:	Remi Denis-Courmont <courmisch@gmail.com>
 S:	Supported

drivers/input/joystick/Kconfig

@@ -362,4 +362,14 @@ config JOYSTICK_PXRC
 	  To compile this driver as a module, choose M here: the
 	  module will be called pxrc.
 
+config JOYSTICK_FSIA6B
+	tristate "FlySky FS-iA6B RC Receiver"
+	select SERIO
+	help
+	  Say Y here if you use a FlySky FS-i6 RC remote control along with the
+	  FS-iA6B RC receiver as a joystick input device.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called fsia6b.
+
 endif

drivers/input/joystick/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_JOYSTICK_AS5011)		+= as5011.o
 obj-$(CONFIG_JOYSTICK_ANALOG)		+= analog.o
 obj-$(CONFIG_JOYSTICK_COBRA)		+= cobra.o
 obj-$(CONFIG_JOYSTICK_DB9)		+= db9.o
+obj-$(CONFIG_JOYSTICK_FSIA6B)		+= fsia6b.o
 obj-$(CONFIG_JOYSTICK_GAMECON)		+= gamecon.o
 obj-$(CONFIG_JOYSTICK_GF2K)		+= gf2k.o
 obj-$(CONFIG_JOYSTICK_GRIP)		+= grip.o
@@ -23,7 +24,7 @@ obj-$(CONFIG_JOYSTICK_JOYDUMP)		+= joydump.o
 obj-$(CONFIG_JOYSTICK_MAGELLAN)		+= magellan.o
 obj-$(CONFIG_JOYSTICK_MAPLE)		+= maplecontrol.o
 obj-$(CONFIG_JOYSTICK_PSXPAD_SPI)	+= psxpad-spi.o
-obj-$(CONFIG_JOYSTICK_PXRC)			+= pxrc.o
+obj-$(CONFIG_JOYSTICK_PXRC)		+= pxrc.o
 obj-$(CONFIG_JOYSTICK_SIDEWINDER)	+= sidewinder.o
 obj-$(CONFIG_JOYSTICK_SPACEBALL)	+= spaceball.o
 obj-$(CONFIG_JOYSTICK_SPACEORB)		+= spaceorb.o
@@ -32,7 +33,7 @@ obj-$(CONFIG_JOYSTICK_TMDC)		+= tmdc.o
 obj-$(CONFIG_JOYSTICK_TURBOGRAFX)	+= turbografx.o
 obj-$(CONFIG_JOYSTICK_TWIDJOY)		+= twidjoy.o
 obj-$(CONFIG_JOYSTICK_WARRIOR)		+= warrior.o
+obj-$(CONFIG_JOYSTICK_WALKERA0701)	+= walkera0701.o
 obj-$(CONFIG_JOYSTICK_XPAD)		+= xpad.o
 obj-$(CONFIG_JOYSTICK_ZHENHUA)		+= zhenhua.o
-obj-$(CONFIG_JOYSTICK_WALKERA0701)	+= walkera0701.o
 

drivers/input/joystick/fsia6b.c

@@ -0,0 +1,231 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * FS-iA6B iBus RC receiver driver
+ *
+ * This driver provides all 14 channels of the FlySky FS-ia6B RC receiver
+ * as analog values.
+ *
+ * Additionally, the channels can be converted to discrete switch values.
+ * By default, it is configured for the offical FS-i6 remote control.
+ * If you use a different hardware configuration, you can configure it
+ * using the `switch_config` parameter.
+ */
+
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/serio.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#define DRIVER_DESC		"FS-iA6B iBus RC receiver"
+
+MODULE_AUTHOR("Markus Koch <markus@notsyncing.net>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define IBUS_SERVO_COUNT	14
+
+static char *switch_config = "00000022320000";
+module_param(switch_config, charp, 0444);
+MODULE_PARM_DESC(switch_config,
+		 "Amount of switch positions per channel (14 characters, 0-3)");
+
+static int fsia6b_axes[IBUS_SERVO_COUNT] = {
+	ABS_X, ABS_Y,
+	ABS_Z, ABS_RX,
+	ABS_RY, ABS_RZ,
+	ABS_HAT0X, ABS_HAT0Y,
+	ABS_HAT1X, ABS_HAT1Y,
+	ABS_HAT2X, ABS_HAT2Y,
+	ABS_HAT3X, ABS_HAT3Y
+};
+
+enum ibus_state { SYNC, COLLECT, PROCESS };
+
+struct ibus_packet {
+	enum ibus_state state;
+
+	int offset;
+	u16 ibuf;
+	u16 channel[IBUS_SERVO_COUNT];
+};
+
+struct fsia6b {
+	struct input_dev *dev;
+	struct ibus_packet packet;
+
+	char phys[32];
+};
+
+static irqreturn_t fsia6b_serio_irq(struct serio *serio,
+				    unsigned char data, unsigned int flags)
+{
+	struct fsia6b *fsia6b = serio_get_drvdata(serio);
+	int i;
+	int sw_state;
+	int sw_id = BTN_0;
+
+	fsia6b->packet.ibuf = (data << 8) | ((fsia6b->packet.ibuf >> 8) & 0xFF);
+
+	switch (fsia6b->packet.state) {
+	case SYNC:
+		if (fsia6b->packet.ibuf == 0x4020)
+			fsia6b->packet.state = COLLECT;
+		break;
+
+	case COLLECT:
+		fsia6b->packet.state = PROCESS;
+		break;
+
+	case PROCESS:
+		fsia6b->packet.channel[fsia6b->packet.offset] =
+				fsia6b->packet.ibuf;
+		fsia6b->packet.offset++;
+
+		if (fsia6b->packet.offset == IBUS_SERVO_COUNT) {
+			fsia6b->packet.offset = 0;
+			fsia6b->packet.state = SYNC;
+			for (i = 0; i < IBUS_SERVO_COUNT; ++i) {
+				input_report_abs(fsia6b->dev, fsia6b_axes[i],
+						 fsia6b->packet.channel[i]);
+
+				sw_state = 0;
+				if (fsia6b->packet.channel[i] > 1900)
+					sw_state = 1;
+				else if (fsia6b->packet.channel[i] < 1100)
+					sw_state = 2;
+
+				switch (switch_config[i]) {
+				case '3':
+					input_report_key(fsia6b->dev,
+							 sw_id++,
+							 sw_state == 0);
+					/* fall-through */
+				case '2':
+					input_report_key(fsia6b->dev,
+							 sw_id++,
+							 sw_state == 1);
+					/* fall-through */
+				case '1':
+					input_report_key(fsia6b->dev,
+							 sw_id++,
+							 sw_state == 2);
+				}
+			}
+			input_sync(fsia6b->dev);
+		} else {
+			fsia6b->packet.state = COLLECT;
+		}
+		break;
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int fsia6b_serio_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct fsia6b *fsia6b;
+	struct input_dev *input_dev;
+	int err;
+	int i, j;
+	int sw_id = 0;
+
+	fsia6b = kzalloc(sizeof(*fsia6b), GFP_KERNEL);
+	if (!fsia6b)
+		return -ENOMEM;
+
+	fsia6b->packet.ibuf = 0;
+	fsia6b->packet.offset = 0;
+	fsia6b->packet.state = SYNC;
+
+	serio_set_drvdata(serio, fsia6b);
+
+	input_dev = input_allocate_device();
+	if (!input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+	fsia6b->dev = input_dev;
+
+	snprintf(fsia6b->phys, sizeof(fsia6b->phys), "%s/input0", serio->phys);
+
+	input_dev->name = DRIVER_DESC;
+	input_dev->phys = fsia6b->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_FSIA6B;
+	input_dev->id.product = serio->id.id;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	for (i = 0; i < IBUS_SERVO_COUNT; i++)
+		input_set_abs_params(input_dev, fsia6b_axes[i],
+				     1000, 2000, 2, 2);
+
+	/* Register switch configuration */
+	for (i = 0; i < IBUS_SERVO_COUNT; i++) {
+		if (switch_config[i] < '0' || switch_config[i] > '3') {
+			dev_err(&fsia6b->dev->dev,
+				"Invalid switch configuration supplied for fsia6b.\n");
+			err = -EINVAL;
+			goto fail2;
+		}
+
+		for (j = '1'; j <= switch_config[i]; j++) {
+			input_set_capability(input_dev, EV_KEY, BTN_0 + sw_id);
+			sw_id++;
+		}
+	}
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(fsia6b->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+fail3:	serio_close(serio);
+fail2:	input_free_device(input_dev);
+fail1:	serio_set_drvdata(serio, NULL);
+	kfree(fsia6b);
+	return err;
+}
+
+static void fsia6b_serio_disconnect(struct serio *serio)
+{
+	struct fsia6b *fsia6b = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(fsia6b->dev);
+	kfree(fsia6b);
+}
+
+static const struct serio_device_id fsia6b_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_FSIA6B,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, fsia6b_serio_ids);
+
+static struct serio_driver fsia6b_serio_drv = {
+	.driver		= {
+		.name	= "fsia6b"
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= fsia6b_serio_ids,
+	.interrupt	= fsia6b_serio_irq,
+	.connect	= fsia6b_serio_connect,
+	.disconnect	= fsia6b_serio_disconnect
+};
+
+module_serio_driver(fsia6b_serio_drv)

include/uapi/linux/serio.h

@@ -82,5 +82,6 @@
 #define SERIO_EGALAX	0x3f
 #define SERIO_PULSE8_CEC	0x40
 #define SERIO_RAINSHADOW_CEC	0x41
+#define SERIO_FSIA6B	0x42
 
 #endif /* _UAPI_SERIO_H */