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 <jhovold@gmail.com>
Acked-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

3 files changed, 53 insertions, 3 deletions

diff --git a/Documentation/input/rotary-encoder.txt b/Documentation/input/rotary-encoder.txt
index 943e8f6f2b15..92e68bce13a4 100644
--- a/Documentation/input/rotary-encoder.txt
+++ b/Documentation/input/rotary-encoder.txt
@@ -9,6 +9,9 @@ peripherals with two wires. The outputs are phase-shifted by 90 degrees
 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:
 
                   _____       _____       _____
@@ -26,6 +29,8 @@ 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
@@ -34,6 +39,13 @@ For more information, please see
 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
 
@@ -96,6 +108,7 @@ static struct rotary_encoder_platform_data my_rotary_encoder_info = {
         .gpio_b         = GPIO_ROTARY_B,
         .inverted_a     = 0,
         .inverted_b     = 0,
+        .half_period    = false,
 };
 
 static struct platform_device rotary_encoder_device = {
diff --git a/drivers/input/misc/rotary_encoder.c b/drivers/input/misc/rotary_encoder.c
index 077b80bdca69..2c8b84dd9dac 100644
--- a/drivers/input/misc/rotary_encoder.c
+++ b/drivers/input/misc/rotary_encoder.c
@@ -2,6 +2,7 @@
  * rotary_encoder.c
  *
  * (c) 2009 Daniel Mack <daniel@caiaq.de>
+ * Copyright (C) 2011 Johan Hovold <jhovold@gmail.com>
  *
  * state machine code inspired by code from Tim Ruetz
  *
@@ -38,6 +39,8 @@ struct rotary_encoder {
 
         bool armed;
         unsigned char dir;      /* 0 - clockwise, 1 - CCW */
+
+        char last_stable;
 };
 
 static int rotary_encoder_get_state(struct rotary_encoder_platform_data *pdata)
@@ -112,11 +115,37 @@ static irqreturn_t rotary_encoder_irq(int irq, void *dev_id)
         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) {
@@ -187,7 +216,14 @@ static int __devinit rotary_encoder_probe(struct platform_device *pdev)
         }
 
         /* 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) {
@@ -196,7 +232,7 @@ static int __devinit rotary_encoder_probe(struct platform_device *pdev)
                 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) {
@@ -264,5 +300,5 @@ module_exit(rotary_encoder_exit);
 
 MODULE_ALIAS("platform:" DRV_NAME);
 MODULE_DESCRIPTION("GPIO rotary encoder driver");
-MODULE_AUTHOR("Daniel Mack <daniel@caiaq.de>");
+MODULE_AUTHOR("Daniel Mack <daniel@caiaq.de>, Johan Hovold");
 MODULE_LICENSE("GPL v2");
diff --git a/include/linux/rotary_encoder.h b/include/linux/rotary_encoder.h
index 215278b8df2a..3f594dce5716 100644
--- a/include/linux/rotary_encoder.h
+++ b/include/linux/rotary_encoder.h
@@ -10,6 +10,7 @@ struct rotary_encoder_platform_data {
         unsigned int inverted_b;
         bool relative_axis;
         bool rollover;
+        bool half_period;
 };
 
 #endif /* __ROTARY_ENCODER_H__ */