Input: rotary_encoder - add support for REL_* axes

The rotary encoder driver only supports returning input events
for ABS_* axes, this adds support for REL_* axes. The relative
axis input event is reported as -1 for each counter-clockwise
step and +1 for each clockwise step.

The ability to clamp the position of ABS_* axes between 0 and
a maximum of "steps" has also been added.

Signed-off-by: H Hartley Sweeten <[e-mail]>
Signed-off-by: Daniel Mack <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/input/rotary-encoder.txt

···
 struct rotary_encoder_platform_data is declared in
 include/linux/rotary-encoder.h and needs to be filled with the number of
 steps the encoder has and can carry information about externally inverted
-signals (because of used invertig buffer or other reasons).
+signals (because of an inverting buffer or other reasons). The encoder
+can be set up to deliver input information as either an absolute or relative
+axes. For relative axes the input event returns +/-1 for each step. For
+absolute axes the position of the encoder can either roll over between zero
+and the number of steps or will clamp at the maximum and zero depending on
+the configuration.
 
 Because GPIO to IRQ mapping is platform specific, this information must
 be given in seperately to the driver. See the example below.
···
 static struct rotary_encoder_platform_data my_rotary_encoder_info = {
 	.steps		= 24,
 	.axis		= ABS_X,
+	.relative_axis	= false,
+	.rollover	= false,
 	.gpio_a		= GPIO_ROTARY_A,
 	.gpio_b		= GPIO_ROTARY_B,
 	.inverted_a	= 0,

drivers/input/misc/rotary_encoder.c

···
 #define DRV_NAME "rotary-encoder"
 
 struct rotary_encoder {
-	unsigned int irq_a;
-	unsigned int irq_b;
-	unsigned int pos;
-	unsigned int armed;
-	unsigned int dir;
 	struct input_dev *input;
 	struct rotary_encoder_platform_data *pdata;
+
+	unsigned int axis;
+	unsigned int pos;
+
+	unsigned int irq_a;
+	unsigned int irq_b;
+
+	bool armed;
+	unsigned char dir;	/* 0 - clockwise, 1 - CCW */
 };
 
 static irqreturn_t rotary_encoder_irq(int irq, void *dev_id)
···
 		if (!encoder->armed)
 			break;
 
-		if (encoder->dir) {
-			/* turning counter-clockwise */
-			encoder->pos += pdata->steps;
-			encoder->pos--;
-			encoder->pos %= pdata->steps;
+		if (pdata->relative_axis) {
+			input_report_rel(encoder->input, pdata->axis,
+					 encoder->dir ? -1 : 1);
 		} else {
-			/* turning clockwise */
-			encoder->pos++;
-			encoder->pos %= pdata->steps;
-		}
+			unsigned int pos = encoder->pos;
 
-		input_report_abs(encoder->input, pdata->axis, encoder->pos);
+			if (encoder->dir) {
+				/* turning counter-clockwise */
+				if (pdata->rollover)
+					pos += pdata->steps;
+				if (pos)
+					pos--;
+			} else {
+				/* turning clockwise */
+				if (pdata->rollover || pos < pdata->steps)
+					pos++;
+			}
+			if (pdata->rollover)
+				pos %= pdata->steps;
+			encoder->pos = pos;
+			input_report_abs(encoder->input, pdata->axis,
+					 encoder->pos);
+		}
 		input_sync(encoder->input);
 
-		encoder->armed = 0;
+		encoder->armed = false;
 		break;
 
 	case 0x1:
···
 		break;
 
 	case 0x3:
-		encoder->armed = 1;
+		encoder->armed = true;
 		break;
 	}
 
···
 	input->name = pdev->name;
 	input->id.bustype = BUS_HOST;
 	input->dev.parent = &pdev->dev;
-	input->evbit[0] = BIT_MASK(EV_ABS);
-	input_set_abs_params(encoder->input,
-			     pdata->axis, 0, pdata->steps, 0, 1);
+
+	if (pdata->relative_axis) {
+		input->evbit[0] = BIT_MASK(EV_REL);
+		input->relbit[0] = BIT_MASK(pdata->axis);
+	} else {
+		input->evbit[0] = BIT_MASK(EV_ABS);
+		input_set_abs_params(encoder->input,
+				     pdata->axis, 0, pdata->steps, 0, 1);
+	}
 
 	err = input_register_device(input);
 	if (err) {

include/linux/rotary_encoder.h

···
 	unsigned int gpio_b;
 	unsigned int inverted_a;
 	unsigned int inverted_b;
+	bool relative_axis;
+	bool rollover;
 };
 
 #endif /* __ROTARY_ENCODER_H__ */