Input: driver for Adafruit Seesaw Gamepad

Adds a driver for a mini gamepad that communicates over i2c, the gamepad
has bidirectional thumb stick input and six buttons.

The gamepad chip utilizes the open framework from Adafruit called 'Seesaw'
to transmit the ADC data for the joystick and digital pin state for the
buttons. I have only implemented the functionality required to receive the
thumb stick and button state.

Steps in reading the gamepad state over i2c:
1. Reset the registers
2. Set the pin mode of the pins specified by the `BUTTON_MASK` to input
`BUTTON_MASK`: A bit-map for the six digital pins internally
connected to the joystick buttons.
3. Enable internal pullup resistors for the `BUTTON_MASK`
4. Bulk set the pin state HIGH for `BUTTON_MASK`
5. Poll the device for button and joystick state done by:
`seesaw_read_data(struct i2c_client *client, struct seesaw_data *data)`

Product page:
https://www.adafruit.com/product/5743
Arduino driver:
https://github.com/adafruit/Adafruit_Seesaw

Driver tested on RPi Zero 2W

Reviewed-by: Thomas Weißschuh <[e-mail]>
Signed-off-by: Anshul Dalal <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

MAINTAINERS

···
 W:	https://ez.analog.com/linux-software-drivers
 F:	drivers/input/touchscreen/ad7879.c
 
+ADAFRUIT MINI I2C GAMEPAD
+M:	Anshul Dalal <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	Documentation/devicetree/bindings/input/adafruit,seesaw-gamepad.yaml
+F:	drivers/input/joystick/adafruit-seesaw.c
+
 ADDRESS SPACE LAYOUT RANDOMIZATION (ASLR)
 M:	Jiri Kosina <[e-mail]>
 S:	Maintained

drivers/input/joystick/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called sensehat_joystick.
 
+config JOYSTICK_SEESAW
+	tristate "Adafruit Mini I2C Gamepad with Seesaw"
+	depends on I2C
+	select INPUT_SPARSEKMAP
+	help
+	  Say Y here if you want to use the Adafruit Mini I2C Gamepad.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called adafruit-seesaw.
+
 endif

drivers/input/joystick/Makefile

···
 obj-$(CONFIG_JOYSTICK_PSXPAD_SPI)	+= psxpad-spi.o
 obj-$(CONFIG_JOYSTICK_PXRC)		+= pxrc.o
 obj-$(CONFIG_JOYSTICK_QWIIC)		+= qwiic-joystick.o
+obj-$(CONFIG_JOYSTICK_SEESAW)		+= adafruit-seesaw.o
 obj-$(CONFIG_JOYSTICK_SENSEHAT)	+= sensehat-joystick.o
 obj-$(CONFIG_JOYSTICK_SIDEWINDER)	+= sidewinder.o
 obj-$(CONFIG_JOYSTICK_SPACEBALL)	+= spaceball.o

drivers/input/joystick/adafruit-seesaw.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2023 Anshul Dalal <[e-mail]>
+ *
+ * Driver for Adafruit Mini I2C Gamepad
+ *
+ * Based on the work of:
+ *	Oleh Kravchenko (Sparkfun Qwiic Joystick driver)
+ *
+ * Datasheet: https://cdn-learn.adafruit.com/downloads/pdf/gamepad-qt.pdf
+ * Product page: https://www.adafruit.com/product/5743
+ * Firmware and hardware sources: https://github.com/adafruit/Adafruit_Seesaw
+ *
+ * TODO:
+ *	- Add interrupt support
+ */
+
+#include <asm/unaligned.h>
+#include <linux/bits.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/input.h>
+#include <linux/input/sparse-keymap.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#define SEESAW_DEVICE_NAME		"seesaw-gamepad"
+
+#define SEESAW_ADC_BASE			0x0900
+
+#define SEESAW_GPIO_DIRCLR_BULK		0x0103
+#define SEESAW_GPIO_BULK		0x0104
+#define SEESAW_GPIO_BULK_SET		0x0105
+#define SEESAW_GPIO_PULLENSET		0x010b
+
+#define SEESAW_STATUS_HW_ID		0x0001
+#define SEESAW_STATUS_SWRST		0x007f
+
+#define SEESAW_ADC_OFFSET		0x07
+
+#define SEESAW_BUTTON_A			0x05
+#define SEESAW_BUTTON_B			0x01
+#define SEESAW_BUTTON_X			0x06
+#define SEESAW_BUTTON_Y			0x02
+#define SEESAW_BUTTON_START		0x10
+#define SEESAW_BUTTON_SELECT		0x00
+
+#define SEESAW_ANALOG_X			0x0e
+#define SEESAW_ANALOG_Y			0x0f
+
+#define SEESAW_JOYSTICK_MAX_AXIS	1023
+#define SEESAW_JOYSTICK_FUZZ		2
+#define SEESAW_JOYSTICK_FLAT		4
+
+#define SEESAW_GAMEPAD_POLL_INTERVAL_MS	16
+#define SEESAW_GAMEPAD_POLL_MIN		8
+#define SEESAW_GAMEPAD_POLL_MAX		32
+
+static const unsigned long SEESAW_BUTTON_MASK =
+	BIT(SEESAW_BUTTON_A) | BIT(SEESAW_BUTTON_B) | BIT(SEESAW_BUTTON_X) |
+	BIT(SEESAW_BUTTON_Y) | BIT(SEESAW_BUTTON_START) |
+	BIT(SEESAW_BUTTON_SELECT);
+
+struct seesaw_gamepad {
+	struct input_dev *input_dev;
+	struct i2c_client *i2c_client;
+};
+
+struct seesaw_data {
+	u16 x;
+	u16 y;
+	u32 button_state;
+};
+
+static const struct key_entry seesaw_buttons_new[] = {
+	{ KE_KEY, SEESAW_BUTTON_A, .keycode = BTN_SOUTH },
+	{ KE_KEY, SEESAW_BUTTON_B, .keycode = BTN_EAST },
+	{ KE_KEY, SEESAW_BUTTON_X, .keycode = BTN_NORTH },
+	{ KE_KEY, SEESAW_BUTTON_Y, .keycode = BTN_WEST },
+	{ KE_KEY, SEESAW_BUTTON_START, .keycode = BTN_START },
+	{ KE_KEY, SEESAW_BUTTON_SELECT, .keycode = BTN_SELECT },
+	{ KE_END, 0 }
+};
+
+static int seesaw_register_read(struct i2c_client *client, u16 reg, void *buf,
+				int count)
+{
+	__be16 register_buf = cpu_to_be16(reg);
+	struct i2c_msg message_buf[2] = {
+		{
+			.addr = client->addr,
+			.flags = client->flags,
+			.len = sizeof(register_buf),
+			.buf = (u8 *)&register_buf,
+		},
+		{
+			.addr = client->addr,
+			.flags = client->flags | I2C_M_RD,
+			.len = count,
+			.buf = (u8 *)buf,
+		},
+	};
+	int ret;
+
+	ret = i2c_transfer(client->adapter, message_buf,
+			   ARRAY_SIZE(message_buf));
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int seesaw_register_write_u8(struct i2c_client *client, u16 reg,
+				    u8 value)
+{
+	u8 write_buf[sizeof(reg) + sizeof(value)];
+	int ret;
+
+	put_unaligned_be16(reg, write_buf);
+	write_buf[sizeof(reg)] = value;
+
+	ret = i2c_master_send(client, write_buf, sizeof(write_buf));
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int seesaw_register_write_u32(struct i2c_client *client, u16 reg,
+				     u32 value)
+{
+	u8 write_buf[sizeof(reg) + sizeof(value)];
+	int ret;
+
+	put_unaligned_be16(reg, write_buf);
+	put_unaligned_be32(value, write_buf + sizeof(reg));
+	ret = i2c_master_send(client, write_buf, sizeof(write_buf));
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int seesaw_read_data(struct i2c_client *client, struct seesaw_data *data)
+{
+	__be16 adc_data;
+	__be32 read_buf;
+	int err;
+
+	err = seesaw_register_read(client, SEESAW_GPIO_BULK,
+				   &read_buf, sizeof(read_buf));
+	if (err)
+		return err;
+
+	data->button_state = ~be32_to_cpu(read_buf);
+
+	err = seesaw_register_read(client,
+				   SEESAW_ADC_BASE |
+					(SEESAW_ADC_OFFSET + SEESAW_ANALOG_X),
+				   &adc_data, sizeof(adc_data));
+	if (err)
+		return err;
+	/*
+	 * ADC reads left as max and right as 0, must be reversed since kernel
+	 * expects reports in opposite order.
+	 */
+	data->x = SEESAW_JOYSTICK_MAX_AXIS - be16_to_cpu(adc_data);
+
+	err = seesaw_register_read(client,
+				   SEESAW_ADC_BASE |
+					(SEESAW_ADC_OFFSET + SEESAW_ANALOG_Y),
+				   &adc_data, sizeof(adc_data));
+	if (err)
+		return err;
+
+	data->y = be16_to_cpu(adc_data);
+
+	return 0;
+}
+
+static void seesaw_poll(struct input_dev *input)
+{
+	struct seesaw_gamepad *private = input_get_drvdata(input);
+	struct seesaw_data data;
+	int err, i;
+
+	err = seesaw_read_data(private->i2c_client, &data);
+	if (err) {
+		dev_err_ratelimited(&input->dev,
+				    "failed to read joystick state: %d\n", err);
+		return;
+	}
+
+	input_report_abs(input, ABS_X, data.x);
+	input_report_abs(input, ABS_Y, data.y);
+
+	for_each_set_bit(i, &SEESAW_BUTTON_MASK,
+			 BITS_PER_TYPE(SEESAW_BUTTON_MASK)) {
+		if (!sparse_keymap_report_event(input, i,
+						data.button_state & BIT(i),
+						false))
+			dev_err_ratelimited(&input->dev,
+					    "failed to report keymap event");
+	}
+
+	input_sync(input);
+}
+
+static int seesaw_probe(struct i2c_client *client)
+{
+	struct seesaw_gamepad *seesaw;
+	u8 hardware_id;
+	int err;
+
+	err = seesaw_register_write_u8(client, SEESAW_STATUS_SWRST, 0xFF);
+	if (err)
+		return err;
+
+	/* Wait for the registers to reset before proceeding */
+	usleep_range(10000, 15000);
+
+	seesaw = devm_kzalloc(&client->dev, sizeof(*seesaw), GFP_KERNEL);
+	if (!seesaw)
+		return -ENOMEM;
+
+	err = seesaw_register_read(client, SEESAW_STATUS_HW_ID,
+				   &hardware_id, sizeof(hardware_id));
+	if (err)
+		return err;
+
+	dev_dbg(&client->dev, "Adafruit Seesaw Gamepad, Hardware ID: %02x\n",
+		hardware_id);
+
+	/* Set Pin Mode to input and enable pull-up resistors */
+	err = seesaw_register_write_u32(client, SEESAW_GPIO_DIRCLR_BULK,
+					SEESAW_BUTTON_MASK);
+	if (err)
+		return err;
+	err = seesaw_register_write_u32(client, SEESAW_GPIO_PULLENSET,
+					SEESAW_BUTTON_MASK);
+	if (err)
+		return err;
+	err = seesaw_register_write_u32(client, SEESAW_GPIO_BULK_SET,
+					SEESAW_BUTTON_MASK);
+	if (err)
+		return err;
+
+	seesaw->i2c_client = client;
+	seesaw->input_dev = devm_input_allocate_device(&client->dev);
+	if (!seesaw->input_dev)
+		return -ENOMEM;
+
+	seesaw->input_dev->id.bustype = BUS_I2C;
+	seesaw->input_dev->name = "Adafruit Seesaw Gamepad";
+	seesaw->input_dev->phys = "i2c/" SEESAW_DEVICE_NAME;
+	input_set_drvdata(seesaw->input_dev, seesaw);
+	input_set_abs_params(seesaw->input_dev, ABS_X,
+			     0, SEESAW_JOYSTICK_MAX_AXIS,
+			     SEESAW_JOYSTICK_FUZZ, SEESAW_JOYSTICK_FLAT);
+	input_set_abs_params(seesaw->input_dev, ABS_Y,
+			     0, SEESAW_JOYSTICK_MAX_AXIS,
+			     SEESAW_JOYSTICK_FUZZ, SEESAW_JOYSTICK_FLAT);
+
+	err = sparse_keymap_setup(seesaw->input_dev, seesaw_buttons_new, NULL);
+	if (err) {
+		dev_err(&client->dev,
+			"failed to set up input device keymap: %d\n", err);
+		return err;
+	}
+
+	err = input_setup_polling(seesaw->input_dev, seesaw_poll);
+	if (err) {
+		dev_err(&client->dev, "failed to set up polling: %d\n", err);
+		return err;
+	}
+
+	input_set_poll_interval(seesaw->input_dev,
+				SEESAW_GAMEPAD_POLL_INTERVAL_MS);
+	input_set_max_poll_interval(seesaw->input_dev, SEESAW_GAMEPAD_POLL_MAX);
+	input_set_min_poll_interval(seesaw->input_dev, SEESAW_GAMEPAD_POLL_MIN);
+
+	err = input_register_device(seesaw->input_dev);
+	if (err) {
+		dev_err(&client->dev, "failed to register joystick: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+static const struct i2c_device_id seesaw_id_table[] = {
+	{ SEESAW_DEVICE_NAME },
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(i2c, seesaw_id_table);
+
+static const struct of_device_id seesaw_of_table[] = {
+	{ .compatible = "adafruit,seesaw-gamepad"},
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, seesaw_of_table);
+
+static struct i2c_driver seesaw_driver = {
+	.driver = {
+		.name = SEESAW_DEVICE_NAME,
+		.of_match_table = seesaw_of_table,
+	},
+	.id_table = seesaw_id_table,
+	.probe = seesaw_probe,
+};
+module_i2c_driver(seesaw_driver);
+
+MODULE_AUTHOR("Anshul Dalal <[e-mail]>");
+MODULE_DESCRIPTION("Adafruit Mini I2C Gamepad driver");
+MODULE_LICENSE("GPL");