Input: mms114 - add support for touch keys

MELFAS MMS114 and similar touchscreens have support for touch keys.
Enable support of them in the driver. The keycodes to emit can be
controlled by the linux,keycodes DT property.

Sidenote - the MAX_TOUCHKEYS value is set to 15, as that's the
maximum value that the ID field can contain. I don't have access
to any datasheets that could confirm or deny whether this is accurate.

Most downstream drivers I've been able to find only use up to 2 keys
(though I did find a driver that mentioned up to 4, but only 2 were
used). They don't have any checks for a maximum keycode value, it is
just extracted from the ID bits (0xf mask).

The drivers I've been able to find also don't use touch ID 0; I assume
that it is never used, so the keycodes provided in the DT start from
touch ID 1. I suppose this is in-line with the regular behavior
for touch IDs in touchscreen events, as there the provided touch ID
is always lowered by 1, which would cause an overflow if it was 0...
Just in case, we quietly return if the touch ID is set to 0 here.

The implementation of the linux,keycodes property handling code was
adapted from the msg2638 driver.

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

drivers/input/touchscreen/mms114.c

···
 /* Touchscreen absolute values */
 #define MMS114_MAX_AREA			0xff
 
+#define MMS114_MAX_TOUCHKEYS		15
 #define MMS114_MAX_TOUCH		10
 #define MMS114_EVENT_SIZE		8
 #define MMS136_EVENT_SIZE		6
···
 	enum mms_type		type;
 	unsigned int		contact_threshold;
 	unsigned int		moving_threshold;
+
+	u32 keycodes[MMS114_MAX_TOUCHKEYS];
+	int num_keycodes;
 
 	/* Use cache data for mode control register(write only) */
 	u8			cache_mode_control;
···
 		return;
 	}
 
-	if (touch->type != MMS114_TYPE_TOUCHSCREEN) {
-		dev_err(&client->dev, "Wrong touch type (%d)\n", touch->type);
-		return;
-	}
-
 	id = touch->id - 1;
 	x = touch->x_lo | touch->x_hi << 8;
 	y = touch->y_lo | touch->y_hi << 8;
···
 	}
 }
 
+static void mms114_process_touchkey(struct mms114_data *data,
+				    struct mms114_touch *touch)
+{
+	struct i2c_client *client = data->client;
+	struct input_dev *input_dev = data->input_dev;
+	unsigned int keycode_id;
+
+	if (touch->id == 0)
+		return;
+
+	if (touch->id > data->num_keycodes) {
+		dev_err(&client->dev, "Wrong touch id for touchkey (%d)\n",
+			touch->id);
+		return;
+	}
+
+	keycode_id = touch->id - 1;
+	dev_dbg(&client->dev, "keycode id: %d, pressed: %d\n", keycode_id,
+		touch->pressed);
+
+	input_report_key(input_dev, data->keycodes[keycode_id], touch->pressed);
+}
+
 static irqreturn_t mms114_interrupt(int irq, void *dev_id)
 {
 	struct mms114_data *data = dev_id;
+	struct i2c_client *client = data->client;
 	struct input_dev *input_dev = data->input_dev;
 	struct mms114_touch touch[MMS114_MAX_TOUCH];
 	int packet_size;
···
 	if (error < 0)
 		goto out;
 
-	for (index = 0; index < touch_size; index++)
-		mms114_process_mt(data, touch + index);
+	for (index = 0; index < touch_size; index++) {
+		switch (touch[index].type) {
+		case MMS114_TYPE_TOUCHSCREEN:
+			mms114_process_mt(data, touch + index);
+			break;
+
+		case MMS114_TYPE_TOUCHKEY:
+			mms114_process_touchkey(data, touch + index);
+			break;
+
+		default:
+			dev_err(&client->dev, "Wrong touch type (%d)\n",
+				touch[index].type);
+			break;
+		}
+	}
 
 	input_mt_report_pointer_emulation(data->input_dev, true);
 	input_sync(data->input_dev);
···
 	struct input_dev *input_dev;
 	const void *match_data;
 	int error;
+	int i;
 
 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
 		dev_err(&client->dev, "Not supported I2C adapter\n");
···
 		return -EINVAL;
 
 	data->type = (enum mms_type)match_data;
+
+	data->num_keycodes = device_property_count_u32(&client->dev,
+						       "linux,keycodes");
+	if (data->num_keycodes == -EINVAL) {
+		data->num_keycodes = 0;
+	} else if (data->num_keycodes < 0) {
+		dev_err(&client->dev,
+			"Unable to parse linux,keycodes property: %d\n",
+			data->num_keycodes);
+		return data->num_keycodes;
+	} else if (data->num_keycodes > MMS114_MAX_TOUCHKEYS) {
+		dev_warn(&client->dev,
+			"Found %d linux,keycodes but max is %d, ignoring the rest\n",
+			 data->num_keycodes, MMS114_MAX_TOUCHKEYS);
+		data->num_keycodes = MMS114_MAX_TOUCHKEYS;
+	}
+
+	if (data->num_keycodes > 0) {
+		error = device_property_read_u32_array(&client->dev,
+						       "linux,keycodes",
+						       data->keycodes,
+						       data->num_keycodes);
+		if (error) {
+			dev_err(&client->dev,
+				"Unable to read linux,keycodes values: %d\n",
+				error);
+			return error;
+		}
+
+		input_dev->keycode = data->keycodes;
+		input_dev->keycodemax = data->num_keycodes;
+		input_dev->keycodesize = sizeof(data->keycodes[0]);
+		for (i = 0; i < data->num_keycodes; i++)
+			input_set_capability(input_dev,
+					     EV_KEY, data->keycodes[i]);
+	}
 
 	input_set_capability(input_dev, EV_ABS, ABS_MT_POSITION_X);
 	input_set_capability(input_dev, EV_ABS, ABS_MT_POSITION_Y);