Input: adafruit-seesaw - only report buttons that changed state

If a button has not changed its state when we poll the device the
driver does not need to report it. While duplicate events will be
filtered out by the input core anyway we can do it very cheaply
directly in the driver.

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

drivers/input/joystick/adafruit-seesaw.c

···
 #define SEESAW_GAMEPAD_POLL_MIN		8
 #define SEESAW_GAMEPAD_POLL_MAX		32
 
-static const unsigned long SEESAW_BUTTON_MASK =
+static const u32 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;
+	u32 button_state;
 };
 
 struct seesaw_data {
···
 	return 0;
 }
 
+static int seesaw_open(struct input_dev *input)
+{
+	struct seesaw_gamepad *private = input_get_drvdata(input);
+
+	private->button_state = 0;
+
+	return 0;
+}
+
 static void seesaw_poll(struct input_dev *input)
 {
 	struct seesaw_gamepad *private = input_get_drvdata(input);
 	struct seesaw_data data;
+	unsigned long changed;
 	int err, i;
 
 	err = seesaw_read_data(private->i2c_client, &data);
···
 	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)) {
+	data.button_state &= SEESAW_BUTTON_MASK;
+	changed = private->button_state ^ data.button_state;
+	private->button_state = data.button_state;
+
+	for_each_set_bit(i, &changed, fls(SEESAW_BUTTON_MASK)) {
 		if (!sparse_keymap_report_event(input, i,
 						data.button_state & BIT(i),
 						false))
···
 	seesaw->input_dev->id.bustype = BUS_I2C;
 	seesaw->input_dev->name = "Adafruit Seesaw Gamepad";
 	seesaw->input_dev->phys = "i2c/" SEESAW_DEVICE_NAME;
+	seesaw->input_dev->open = seesaw_open;
 	input_set_drvdata(seesaw->input_dev, seesaw);
 	input_set_abs_params(seesaw->input_dev, ABS_X,
 			     0, SEESAW_JOYSTICK_MAX_AXIS,