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>

5 files changed, 251 insertions, 2 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 677ef41cb012..cdd25b0a1218 100644
--- a/MAINTAINERS
+++ b/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
diff --git a/drivers/input/joystick/Kconfig b/drivers/input/joystick/Kconfig
index 72b932901d00..312b854b5506 100644
--- a/drivers/input/joystick/Kconfig
+++ b/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
diff --git a/drivers/input/joystick/Makefile b/drivers/input/joystick/Makefile
index dd0492ebbed7..8656023f6ef5 100644
--- a/drivers/input/joystick/Makefile
+++ b/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
 
diff --git a/drivers/input/joystick/fsia6b.c b/drivers/input/joystick/fsia6b.c
new file mode 100644
index 000000000000..e78c4c768990
--- /dev/null
+++ b/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)
diff --git a/include/uapi/linux/serio.h b/include/uapi/linux/serio.h
index a0cac1d8670d..50e991952c97 100644
--- a/include/uapi/linux/serio.h
+++ b/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 */