[PATCH v2 0/4] add z1 and z2 channels support for resistive-adc-touch driver

@@ -43,6 +43,7 @@ properties:
   touchscreen-inverted-y: true
   touchscreen-swapped-x-y: true
   touchscreen-min-pressure: true
+  touchscreen-x-plate-ohms: true
 
 additionalProperties: false
 

@@ -59,3 +60,11 @@ examples:
       io-channels = <&adc 24>, <&adc 25>, <&adc 26>;
       io-channel-names = "x", "y", "pressure";
     };
+  - |
+    resistive_touch {
+      compatible = "resistive-adc-touch";
+      touchscreen-min-pressure = <50000>;
+      io-channels = <&adc 1>, <&adc 2>, <&adc 3>, <&adc 4>;
+      io-channel-names = "x", "y", "z1", "z2";
+      touchscreen-x-plate-ohms = <800>;
+    };

@@ -74,6 +74,12 @@ properties:
   touchscreen-y-mm:
     description: vertical length in mm of the touchscreen
 
+  touchscreen-x-plate-ohms:
+    description: Resistance of the X-plate in Ohms
+
+  touchscreen-y-plate-ohms:
+    description: Resistance of the Y-plate in Ohms
+
 dependencies:
   touchscreen-size-x: [ touchscreen-size-y ]
   touchscreen-size-y: [ touchscreen-size-x ]

@@ -20,7 +20,18 @@
 
 #define DRIVER_NAME					"resistive-adc-touch"
 #define GRTS_DEFAULT_PRESSURE_MIN			50000
+#define GRTS_DEFAULT_PRESSURE_MAX			65535
 #define GRTS_MAX_POS_MASK				GENMASK(11, 0)
+#define GRTS_MAX_CHANNELS				4
+
+enum grts_ch_type {
+	GRTS_CH_NONE = 0,
+	GRTS_CH_X,
+	GRTS_CH_Y,
+	GRTS_CH_PRESSURE,
+	GRTS_CH_Z1,
+	GRTS_CH_Z2,
+};
 
 /**
  * struct grts_state - generic resistive touch screen information struct

@@ -33,24 +44,61 @@
  */
 struct grts_state {
 	u32				pressure_min;
+	u32				x_plate_ohms;
 	bool				pressure;
 	struct iio_channel		*iio_chans;
 	struct iio_cb_buffer		*iio_cb;
 	struct input_dev		*input;
 	struct touchscreen_properties	prop;
+	u8				ch[GRTS_MAX_CHANNELS];
 };
 
 static int grts_cb(const void *data, void *private)
 {
 	const u16 *touch_info = data;
 	struct grts_state *st = private;
-	unsigned int x, y, press = 0x0;
+	unsigned int x, y, press = 0, z1 = 0, z2;
+	unsigned int Rt, i;
+
+	for (i = 0; i < ARRAY_SIZE(st->ch) && st->ch[i] != GRTS_CH_NONE; i++) {
+		switch (st->ch[i]) {
+		case GRTS_CH_X:
+			x = touch_info[i];
+			break;
+		case GRTS_CH_Y:
+			y = touch_info[i];
+			break;
+		case GRTS_CH_PRESSURE:
+			press = touch_info[i];
+			break;
+		case GRTS_CH_Z1:
+			z1 = touch_info[i];
+			break;
+		case GRTS_CH_Z2:
+			z2 = touch_info[i];
+			break;
+		case GRTS_CH_NONE:
+			break;
+		}
+	}
 
-	/* channel data coming in buffer in the order below */
-	x = touch_info[0];
-	y = touch_info[1];
-	if (st->pressure)
-		press = touch_info[2];
+	if (z1) {
+		Rt = z2;
+		Rt -= z1;
+		Rt *= st->x_plate_ohms;
+		Rt = DIV_ROUND_CLOSEST(Rt, 16);
+		Rt *= x;
+		Rt /= z1;
+		Rt = DIV_ROUND_CLOSEST(Rt, 256);
+		/*
+		 * On increased pressure the resistance (Rt) is decreasing
+		 * so, convert values to make it looks as real pressure.
+		 */
+		if (Rt < GRTS_DEFAULT_PRESSURE_MAX)
+			press = GRTS_DEFAULT_PRESSURE_MAX - Rt;
+		else
+			press = 0;
+	}
 
 	if ((!x && !y) || (st->pressure && (press < st->pressure_min))) {
 		/* report end of touch */

@@ -94,6 +142,72 @@ static void grts_disable(void *data)
 	iio_channel_release_all_cb(data);
 }
 
+static int grts_get_properties(struct grts_state *st, struct device *dev)
+{
+	int idx, error;
+
+	idx = device_property_match_string(dev, "io-channel-names", "x");
+	if (idx < 0)
+		return idx;
+
+	if (idx >= ARRAY_SIZE(st->ch))
+		return -EOVERFLOW;
+
+	st->ch[idx] = GRTS_CH_X;
+
+	idx = device_property_match_string(dev, "io-channel-names", "y");
+	if (idx < 0)
+		return idx;
+
+	if (idx >= ARRAY_SIZE(st->ch))
+		return -EOVERFLOW;
+
+	st->ch[idx] = GRTS_CH_Y;
+
+	/* pressure is optional */
+	idx = device_property_match_string(dev, "io-channel-names", "pressure");
+	if (idx >= 0) {
+		if (idx >= ARRAY_SIZE(st->ch))
+			return -EOVERFLOW;
+
+		st->ch[idx] = GRTS_CH_PRESSURE;
+		st->pressure = true;
+
+		return 0;
+	}
+
+	/* if no pressure is defined, try optional z1 + z2 */
+	idx = device_property_match_string(dev, "io-channel-names", "z1");
+	if (idx < 0)
+		return 0;
+
+	if (idx >= ARRAY_SIZE(st->ch))
+		return -EOVERFLOW;
+
+	st->ch[idx] = GRTS_CH_Z1;
+
+	/* if z1 is provided z2 is not optional */
+	idx = device_property_match_string(dev, "io-channel-names", "z2");
+	if (idx < 0)
+		return idx;
+
+	if (idx >= ARRAY_SIZE(st->ch))
+		return -EOVERFLOW;
+
+	st->ch[idx] = GRTS_CH_Z2;
+	st->pressure = true;
+
+	error = device_property_read_u32(dev,
+					 "touchscreen-x-plate-ohms",
+					 &st->x_plate_ohms);
+	if (error) {
+		dev_err(dev, "can't get touchscreen-x-plate-ohms property\n");
+		return error;
+	}
+
+	return 0;
+}
+
 static int grts_probe(struct platform_device *pdev)
 {
 	struct grts_state *st;

@@ -115,12 +229,13 @@ static int grts_probe(struct platform_device *pdev)
 		return error;
 	}
 
-	chan = &st->iio_chans[0];
-	st->pressure = false;
-	while (chan && chan->indio_dev) {
-		if (!strcmp(chan->channel->datasheet_name, "pressure"))
-			st->pressure = true;
-		chan++;
+	if (!device_property_present(dev, "io-channel-names"))
+		return -ENODEV;
+
+	error = grts_get_properties(st, dev);
+	if (error) {
+		dev_err(dev, "Failed to parse properties\n");
+		return error;
 	}
 
 	if (st->pressure) {

@@ -148,7 +263,7 @@ static int grts_probe(struct platform_device *pdev)
 	input_set_abs_params(input, ABS_Y, 0, GRTS_MAX_POS_MASK - 1, 0, 0);
 	if (st->pressure)
 		input_set_abs_params(input, ABS_PRESSURE, st->pressure_min,
-				     0xffff, 0, 0);
+				     GRTS_DEFAULT_PRESSURE_MAX, 0, 0);
 
 	input_set_capability(input, EV_KEY, BTN_TOUCH);
 

@@ -1,33 +0,0 @@
-Generic resistive touchscreen ADC
-
-Required properties:
-
- - compatible: must be "resistive-adc-touch"
-The device must be connected to an ADC device that provides channels for
-position measurement and optional pressure.
-Refer to
-https://github.com/devicetree-org/dt-schema/blob/master/schemas/iio/iio-consumer.yaml
-for details
-
- - iio-channels: must have at least two channels connected to an ADC device.
-These should correspond to the channels exposed by the ADC device and should
-have the right index as the ADC device registers them. These channels
-represent the relative position on the "x" and "y" axes.
- - iio-channel-names: must have all the channels' names. Mandatory channels
-are "x" and "y".
-
-Optional properties:
- - iio-channels: The third channel named "pressure" is optional and can be
-used if the ADC device also measures pressure besides position.
-If this channel is missing, pressure will be ignored and the touchscreen
-will only report position.
- - iio-channel-names: optional channel named "pressure".
-
-Example:
-
-	resistive_touch: resistive_touch {
-		compatible = "resistive-adc-touch";
-		touchscreen-min-pressure = <50000>;
-		io-channels = <&adc 24>, <&adc 25>, <&adc 26>;
-		io-channel-names = "x", "y", "pressure";
-	};

@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/input/touchscreen/resistive-adc-touch.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic resistive touchscreen ADC
+
+maintainers:
+  - Oleksij Rempel <o.rempel@pengutronix.de>
+
+description: |
+  Generic ADC based resistive touchscreen controller
+  The device must be connected to an ADC device that provides channels for
+  position measurement and optional pressure.
+
+allOf:
+  - $ref: touchscreen.yaml#
+
+properties:
+  compatible:
+    const: resistive-adc-touch
+
+  io-channels:
+    minItems: 2
+    maxItems: 3
+    items:
+      - description: x
+      - description: y
+      - description: pressure (optional)
+
+  io-channel-names:
+    items:
+      - const: x
+      - const: y
+      - const: pressure
+
+  touchscreen-size-x: true
+  touchscreen-size-y: true
+  touchscreen-fuzz-x: true
+  touchscreen-fuzz-y: true
+  touchscreen-inverted-x: true
+  touchscreen-inverted-y: true
+  touchscreen-swapped-x-y: true
+  touchscreen-min-pressure: true
+
+additionalProperties: false
+
+required:
+  - compatible
+  - io-channels
+  - io-channel-names
+
+examples:
+  - |
+    resistive_touch {
+      compatible = "resistive-adc-touch";
+      touchscreen-min-pressure = <50000>;
+      io-channels = <&adc 24>, <&adc 25>, <&adc 26>;
+      io-channel-names = "x", "y", "pressure";
+    };