Input: rotary-encoder - add support for half-period encoders

Add support for encoders that have two detents per input signal period.

Signed-off-by: Johan Hovold <[e-mail]>
Acked-by: Daniel Mack <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/input/rotary-encoder.txt

···
 and by triggering on falling and rising edges, the turn direction can
 be determined.
 
+Some encoders have both outputs low in stable states, whereas others also have
+a stable state with both outputs high (half-period mode).
+
 The phase diagram of these two outputs look like this:
 
                   _____       _____       _____
···
                 |<-------->|
 	          one step
 
+                |<-->|
+	          one step (half-period mode)
 
 For more information, please see
 	http://en.wikipedia.org/wiki/Rotary_encoder
···
 
 1. Events / state machine
 -------------------------
+
+In half-period mode, state a) and c) above are used to determine the
+rotational direction based on the last stable state. Events are reported in
+states b) and d) given that the new stable state is different from the last
+(i.e. the rotation was not reversed half-way).
+
+Otherwise, the following apply:
 
 a) Rising edge on channel A, channel B in low state
 	This state is used to recognize a clockwise turn
···
 	.gpio_b		= GPIO_ROTARY_B,
 	.inverted_a	= 0,
 	.inverted_b	= 0,
+	.half_period	= false,
 };
 
 static struct platform_device rotary_encoder_device = {

drivers/input/misc/rotary_encoder.c

···
  * rotary_encoder.c
  *
  * (c) 2009 Daniel Mack <[e-mail]>
+ * Copyright (C) 2011 Johan Hovold <[e-mail]>
  *
  * state machine code inspired by code from Tim Ruetz
  *
···
 
 	bool armed;
 	unsigned char dir;	/* 0 - clockwise, 1 - CCW */
+
+	char last_stable;
 };
 
 static int rotary_encoder_get_state(struct rotary_encoder_platform_data *pdata)
···
 	return IRQ_HANDLED;
 }
 
+static irqreturn_t rotary_encoder_half_period_irq(int irq, void *dev_id)
+{
+	struct rotary_encoder *encoder = dev_id;
+	int state;
+
+	state = rotary_encoder_get_state(encoder->pdata);
+
+	switch (state) {
+	case 0x00:
+	case 0x03:
+		if (state != encoder->last_stable) {
+			rotary_encoder_report_event(encoder);
+			encoder->last_stable = state;
+		}
+		break;
+
+	case 0x01:
+	case 0x02:
+		encoder->dir = (encoder->last_stable + state) & 0x01;
+		break;
+	}
+
+	return IRQ_HANDLED;
+}
+
 static int __devinit rotary_encoder_probe(struct platform_device *pdev)
 {
 	struct rotary_encoder_platform_data *pdata = pdev->dev.platform_data;
 	struct rotary_encoder *encoder;
 	struct input_dev *input;
+	irq_handler_t handler;
 	int err;
 
 	if (!pdata) {
···
 	}
 
 	/* request the IRQs */
-	err = request_irq(encoder->irq_a, &rotary_encoder_irq,
+	if (pdata->half_period) {
+		handler = &rotary_encoder_half_period_irq;
+		encoder->last_stable = rotary_encoder_get_state(pdata);
+	} else {
+		handler = &rotary_encoder_irq;
+	}
+
+	err = request_irq(encoder->irq_a, handler,
 			  IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 			  DRV_NAME, encoder);
 	if (err) {
···
 		goto exit_free_gpio_b;
 	}
 
-	err = request_irq(encoder->irq_b, &rotary_encoder_irq,
+	err = request_irq(encoder->irq_b, handler,
 			  IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 			  DRV_NAME, encoder);
 	if (err) {
···
 
 MODULE_ALIAS("platform:" DRV_NAME);
 MODULE_DESCRIPTION("GPIO rotary encoder driver");
-MODULE_AUTHOR("Daniel Mack <[e-mail]>");
+MODULE_AUTHOR("Daniel Mack <[e-mail]>, Johan Hovold");
 MODULE_LICENSE("GPL v2");

include/linux/rotary_encoder.h

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