Input: rotary_encoder - support binary encoding of states

It's not advisable to use this encoding, but to support existing devices
add support for this to the driver.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/rotary-encoder.txt

@@ -20,6 +20,8 @@ Optional properties:
   2: Half-period mode
   4: Quarter-period mode
 - wakeup-source: Boolean, rotary encoder can wake up the system.
+- rotary-encoder,encoding: String, the method used to encode steps.
+  Supported are "gray" (the default and more common) and "binary".
 
 Deprecated properties:
 - rotary-encoder,half-period: Makes the driver work on half-period mode.
@@ -34,6 +36,7 @@ Example:
 			compatible = "rotary-encoder";
 			gpios = <&gpio 19 1>, <&gpio 20 0>; /* GPIO19 is inverted */
 			linux,axis = <0>; /* REL_X */
+			rotary-encoder,encoding = "gray";
 			rotary-encoder,relative-axis;
 		};
 
@@ -42,5 +45,6 @@ Example:
 			gpios = <&gpio 21 0>, <&gpio 22 0>;
 			linux,axis = <1>; /* ABS_Y */
 			rotary-encoder,steps = <24>;
+			rotary-encoder,encoding = "binary";
 			rotary-encoder,rollover;
 		};

drivers/input/misc/rotary_encoder.c

@@ -28,6 +28,11 @@
 
 #define DRV_NAME "rotary-encoder"
 
+enum rotary_encoder_encoding {
+	ROTENC_GRAY,
+	ROTENC_BINARY,
+};
+
 struct rotary_encoder {
 	struct input_dev *input;
 
@@ -37,6 +42,7 @@ struct rotary_encoder {
 	u32 axis;
 	bool relative_axis;
 	bool rollover;
+	enum rotary_encoder_encoding encoding;
 
 	unsigned int pos;
 
@@ -57,8 +63,9 @@ static unsigned int rotary_encoder_get_state(struct rotary_encoder *encoder)
 
 	for (i = 0; i < encoder->gpios->ndescs; ++i) {
 		int val = gpiod_get_value_cansleep(encoder->gpios->desc[i]);
+
 		/* convert from gray encoding to normal */
-		if (ret & 1)
+		if (encoder->encoding == ROTENC_GRAY && ret & 1)
 			val = !val;
 
 		ret = ret << 1 | val;
@@ -213,6 +220,20 @@ static int rotary_encoder_probe(struct platform_device *pdev)
 	encoder->rollover =
 		device_property_read_bool(dev, "rotary-encoder,rollover");
 
+	if (!device_property_present(dev, "rotary-encoder,encoding") ||
+	    !device_property_match_string(dev, "rotary-encoder,encoding",
+					  "gray")) {
+		dev_info(dev, "gray");
+		encoder->encoding = ROTENC_GRAY;
+	} else if (!device_property_match_string(dev, "rotary-encoder,encoding",
+						 "binary")) {
+		dev_info(dev, "binary");
+		encoder->encoding = ROTENC_BINARY;
+	} else {
+		dev_err(dev, "unknown encoding setting\n");
+		return -EINVAL;
+	}
+
 	device_property_read_u32(dev, "linux,axis", &encoder->axis);
 	encoder->relative_axis =
 		device_property_read_bool(dev, "rotary-encoder,relative-axis");