--- /dev/null
+rotary-encoder - a generic driver for GPIO connected devices
+Daniel Mack <daniel@caiaq.de>, Feb 2009
+
+0. Function
+-----------
+
+Rotary encoders are devices which are connected to the CPU or other
+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.
+
+The phase diagram of these two outputs look like this:
+
+ _____ _____ _____
+ | | | | | |
+ Channel A ____| |_____| |_____| |____
+
+ : : : : : : : : : : : :
+ __ _____ _____ _____
+ | | | | | | |
+ Channel B |_____| |_____| |_____| |__
+
+ : : : : : : : : : : : :
+ Event a b c d a b c d a b c d
+
+ |<-------->|
+ one step
+
+
+For more information, please see
+ http://en.wikipedia.org/wiki/Rotary_encoder
+
+
+1. Events / state machine
+-------------------------
+
+a) Rising edge on channel A, channel B in low state
+ This state is used to recognize a clockwise turn
+
+b) Rising edge on channel B, channel A in high state
+ When entering this state, the encoder is put into 'armed' state,
+ meaning that there it has seen half the way of a one-step transition.
+
+c) Falling edge on channel A, channel B in high state
+ This state is used to recognize a counter-clockwise turn
+
+d) Falling edge on channel B, channel A in low state
+ Parking position. If the encoder enters this state, a full transition
+ should have happend, unless it flipped back on half the way. The
+ 'armed' state tells us about that.
+
+2. Platform requirements
+------------------------
+
+As there is no hardware dependent call in this driver, the platform it is
+used with must support gpiolib. Another requirement is that IRQs must be
+able to fire on both edges.
+
+
+3. Board integration
+--------------------
+
+To use this driver in your system, register a platform_device with the
+name 'rotary-encoder' and associate the IRQs and some specific platform
+data with it.
+
+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).
+
+Because GPIO to IRQ mapping is platform specific, this information must
+be given in seperately to the driver. See the example below.
+
+---------<snip>---------
+
+/* board support file example */
+
+#include <linux/input.h>
+#include <linux/rotary_encoder.h>
+
+#define GPIO_ROTARY_A 1
+#define GPIO_ROTARY_B 2
+
+static struct rotary_encoder_platform_data my_rotary_encoder_info = {
+ .steps = 24,
+ .axis = ABS_X,
+ .gpio_a = GPIO_ROTARY_A,
+ .gpio_b = GPIO_ROTARY_B,
+ .inverted_a = 0,
+ .inverted_b = 0,
+};
+
+static struct platform_device rotary_encoder_device = {
+ .name = "rotary-encoder",
+ .id = 0,
+ .dev = {
+ .platform_data = &my_rotary_encoder_info,
+ }
+};
+
--- /dev/null
+/*
+ * rotary_encoder.c
+ *
+ * (c) 2009 Daniel Mack <daniel@caiaq.de>
+ *
+ * state machine code inspired by code from Tim Ruetz
+ *
+ * A generic driver for rotary encoders connected to GPIO lines.
+ * See file:Documentation/input/rotary_encoder.txt for more information
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/input.h>
+#include <linux/device.h>
+#include <linux/platform_device.h>
+#include <linux/gpio.h>
+#include <linux/rotary_encoder.h>
+
+#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;
+};
+
+static irqreturn_t rotary_encoder_irq(int irq, void *dev_id)
+{
+ struct rotary_encoder *encoder = dev_id;
+ struct rotary_encoder_platform_data *pdata = encoder->pdata;
+ int a = !!gpio_get_value(pdata->gpio_a);
+ int b = !!gpio_get_value(pdata->gpio_b);
+ int state;
+
+ a ^= pdata->inverted_a;
+ b ^= pdata->inverted_b;
+ state = (a << 1) | b;
+
+ switch (state) {
+
+ case 0x0:
+ if (!encoder->armed)
+ break;
+
+ if (encoder->dir) {
+ /* turning counter-clockwise */
+ encoder->pos += pdata->steps;
+ encoder->pos--;
+ encoder->pos %= pdata->steps;
+ } else {
+ /* turning clockwise */
+ encoder->pos++;
+ encoder->pos %= pdata->steps;
+ }
+
+ input_report_abs(encoder->input, pdata->axis, encoder->pos);
+ input_sync(encoder->input);
+
+ encoder->armed = 0;
+ break;
+
+ case 0x1:
+ case 0x2:
+ if (encoder->armed)
+ encoder->dir = state - 1;
+ break;
+
+ case 0x3:
+ encoder->armed = 1;
+ 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;
+ int err;
+
+ if (!pdata || !pdata->steps) {
+ dev_err(&pdev->dev, "invalid platform data\n");
+ return -ENOENT;
+ }
+
+ encoder = kzalloc(sizeof(struct rotary_encoder), GFP_KERNEL);
+ input = input_allocate_device();
+ if (!encoder || !input) {
+ dev_err(&pdev->dev, "failed to allocate memory for device\n");
+ err = -ENOMEM;
+ goto exit_free_mem;
+ }
+
+ encoder->input = input;
+ encoder->pdata = pdata;
+ encoder->irq_a = gpio_to_irq(pdata->gpio_a);
+ encoder->irq_b = gpio_to_irq(pdata->gpio_b);
+
+ /* create and register the input driver */
+ 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);
+
+ err = input_register_device(input);
+ if (err) {
+ dev_err(&pdev->dev, "failed to register input device\n");
+ goto exit_free_mem;
+ }
+
+ /* request the GPIOs */
+ err = gpio_request(pdata->gpio_a, DRV_NAME);
+ if (err) {
+ dev_err(&pdev->dev, "unable to request GPIO %d\n",
+ pdata->gpio_a);
+ goto exit_unregister_input;
+ }
+
+ err = gpio_request(pdata->gpio_b, DRV_NAME);
+ if (err) {
+ dev_err(&pdev->dev, "unable to request GPIO %d\n",
+ pdata->gpio_b);
+ goto exit_free_gpio_a;
+ }
+
+ /* request the IRQs */
+ err = request_irq(encoder->irq_a, &rotary_encoder_irq,
+ IORESOURCE_IRQ_HIGHEDGE | IORESOURCE_IRQ_LOWEDGE,
+ DRV_NAME, encoder);
+ if (err) {
+ dev_err(&pdev->dev, "unable to request IRQ %d\n",
+ encoder->irq_a);
+ goto exit_free_gpio_b;
+ }
+
+ err = request_irq(encoder->irq_b, &rotary_encoder_irq,
+ IORESOURCE_IRQ_HIGHEDGE | IORESOURCE_IRQ_LOWEDGE,
+ DRV_NAME, encoder);
+ if (err) {
+ dev_err(&pdev->dev, "unable to request IRQ %d\n",
+ encoder->irq_b);
+ goto exit_free_irq_a;
+ }
+
+ platform_set_drvdata(pdev, encoder);
+
+ return 0;
+
+exit_free_irq_a:
+ free_irq(encoder->irq_a, encoder);
+exit_free_gpio_b:
+ gpio_free(pdata->gpio_b);
+exit_free_gpio_a:
+ gpio_free(pdata->gpio_a);
+exit_unregister_input:
+ input_unregister_device(input);
+ input = NULL; /* so we don't try to free it */
+exit_free_mem:
+ input_free_device(input);
+ kfree(encoder);
+ return err;
+}
+
+static int __devexit rotary_encoder_remove(struct platform_device *pdev)
+{
+ struct rotary_encoder *encoder = platform_get_drvdata(pdev);
+ struct rotary_encoder_platform_data *pdata = pdev->dev.platform_data;
+
+ free_irq(encoder->irq_a, encoder);
+ free_irq(encoder->irq_b, encoder);
+ gpio_free(pdata->gpio_a);
+ gpio_free(pdata->gpio_b);
+ input_unregister_device(encoder->input);
+ platform_set_drvdata(pdev, NULL);
+ kfree(encoder);
+
+ return 0;
+}
+
+static struct platform_driver rotary_encoder_driver = {
+ .probe = rotary_encoder_probe,
+ .remove = __devexit_p(rotary_encoder_remove),
+ .driver = {
+ .name = DRV_NAME,
+ .owner = THIS_MODULE,
+ }
+};
+
+static int __init rotary_encoder_init(void)
+{
+ return platform_driver_register(&rotary_encoder_driver);
+}
+
+static void __exit rotary_encoder_exit(void)
+{
+ platform_driver_unregister(&rotary_encoder_driver);
+}
+
+module_init(rotary_encoder_init);
+module_exit(rotary_encoder_exit);
+
+MODULE_ALIAS("platform:" DRV_NAME);
+MODULE_DESCRIPTION("GPIO rotary encoder driver");
+MODULE_AUTHOR("Daniel Mack <daniel@caiaq.de>");
+MODULE_LICENSE("GPL v2");
+
projects / GitHub / MotorolaMobilityLLC / kernel-slsi.git / commitdiff