Input: generic driver for rotary encoders on GPIOs
This patch adds a generic driver for rotary encoders connected to GPIO pins of a system. It relies on gpiolib and generic hardware irqs. The documentation that also comes with this patch explains the concept and how to use the driver. Signed-off-by: Daniel Mack <daniel@caiaq.de> Tested-by: H Hartley Sweeten <hsweeten@visionengravers.com> Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
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Daniel Mack
Dmitry Torokhov
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101
Documentation/input/rotary-encoder.txt
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101
Documentation/input/rotary-encoder.txt
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@ -0,0 +1,101 @@
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rotary-encoder - a generic driver for GPIO connected devices
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Daniel Mack <daniel@caiaq.de>, Feb 2009
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0. Function
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-----------
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Rotary encoders are devices which are connected to the CPU or other
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peripherals with two wires. The outputs are phase-shifted by 90 degrees
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and by triggering on falling and rising edges, the turn direction can
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be determined.
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The phase diagram of these two outputs look like this:
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_____ _____ _____
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| | | | | |
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Channel A ____| |_____| |_____| |____
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: : : : : : : : : : : :
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__ _____ _____ _____
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| | | | | | |
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Channel B |_____| |_____| |_____| |__
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: : : : : : : : : : : :
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Event a b c d a b c d a b c d
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|<-------->|
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one step
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For more information, please see
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http://en.wikipedia.org/wiki/Rotary_encoder
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1. Events / state machine
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-------------------------
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a) Rising edge on channel A, channel B in low state
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This state is used to recognize a clockwise turn
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b) Rising edge on channel B, channel A in high state
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When entering this state, the encoder is put into 'armed' state,
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meaning that there it has seen half the way of a one-step transition.
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c) Falling edge on channel A, channel B in high state
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This state is used to recognize a counter-clockwise turn
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d) Falling edge on channel B, channel A in low state
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Parking position. If the encoder enters this state, a full transition
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should have happend, unless it flipped back on half the way. The
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'armed' state tells us about that.
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2. Platform requirements
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------------------------
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As there is no hardware dependent call in this driver, the platform it is
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used with must support gpiolib. Another requirement is that IRQs must be
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able to fire on both edges.
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3. Board integration
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--------------------
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To use this driver in your system, register a platform_device with the
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name 'rotary-encoder' and associate the IRQs and some specific platform
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data with it.
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struct rotary_encoder_platform_data is declared in
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include/linux/rotary-encoder.h and needs to be filled with the number of
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steps the encoder has and can carry information about externally inverted
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signals (because of used invertig buffer or other reasons).
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Because GPIO to IRQ mapping is platform specific, this information must
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be given in seperately to the driver. See the example below.
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---------<snip>---------
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/* board support file example */
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#include <linux/input.h>
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#include <linux/rotary_encoder.h>
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#define GPIO_ROTARY_A 1
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#define GPIO_ROTARY_B 2
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static struct rotary_encoder_platform_data my_rotary_encoder_info = {
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.steps = 24,
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.axis = ABS_X,
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.gpio_a = GPIO_ROTARY_A,
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.gpio_b = GPIO_ROTARY_B,
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.inverted_a = 0,
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.inverted_b = 0,
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};
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static struct platform_device rotary_encoder_device = {
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.name = "rotary-encoder",
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.id = 0,
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.dev = {
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.platform_data = &my_rotary_encoder_info,
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}
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};
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@ -227,4 +227,15 @@ config INPUT_PCF50633_PMU
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Say Y to include support for delivering PMU events via input
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layer on NXP PCF50633.
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config INPUT_GPIO_ROTARY_ENCODER
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tristate "Rotary encoders connected to GPIO pins"
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depends on GPIOLIB && GENERIC_GPIO
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help
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Say Y here to add support for rotary encoders connected to GPIO lines.
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Check file:Documentation/incput/rotary_encoder.txt for more
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information.
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To compile this driver as a module, choose M here: the
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module will be called rotary_encoder.
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endif
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@ -22,3 +22,5 @@ obj-$(CONFIG_INPUT_UINPUT) += uinput.o
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obj-$(CONFIG_INPUT_APANEL) += apanel.o
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obj-$(CONFIG_INPUT_SGI_BTNS) += sgi_btns.o
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obj-$(CONFIG_INPUT_PCF50633_PMU) += pcf50633-input.o
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obj-$(CONFIG_INPUT_GPIO_ROTARY_ENCODER) += rotary_encoder.o
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221
drivers/input/misc/rotary_encoder.c
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221
drivers/input/misc/rotary_encoder.c
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@ -0,0 +1,221 @@
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/*
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* rotary_encoder.c
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*
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* (c) 2009 Daniel Mack <daniel@caiaq.de>
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*
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* state machine code inspired by code from Tim Ruetz
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*
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* A generic driver for rotary encoders connected to GPIO lines.
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* See file:Documentation/input/rotary_encoder.txt for more information
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/interrupt.h>
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#include <linux/input.h>
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#include <linux/device.h>
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#include <linux/platform_device.h>
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#include <linux/gpio.h>
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#include <linux/rotary_encoder.h>
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#define DRV_NAME "rotary-encoder"
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struct rotary_encoder {
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unsigned int irq_a;
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unsigned int irq_b;
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unsigned int pos;
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unsigned int armed;
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unsigned int dir;
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struct input_dev *input;
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struct rotary_encoder_platform_data *pdata;
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};
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static irqreturn_t rotary_encoder_irq(int irq, void *dev_id)
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{
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struct rotary_encoder *encoder = dev_id;
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struct rotary_encoder_platform_data *pdata = encoder->pdata;
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int a = !!gpio_get_value(pdata->gpio_a);
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int b = !!gpio_get_value(pdata->gpio_b);
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int state;
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a ^= pdata->inverted_a;
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b ^= pdata->inverted_b;
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state = (a << 1) | b;
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switch (state) {
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case 0x0:
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if (!encoder->armed)
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break;
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if (encoder->dir) {
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/* turning counter-clockwise */
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encoder->pos += pdata->steps;
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encoder->pos--;
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encoder->pos %= pdata->steps;
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} else {
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/* turning clockwise */
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encoder->pos++;
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encoder->pos %= pdata->steps;
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}
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input_report_abs(encoder->input, pdata->axis, encoder->pos);
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input_sync(encoder->input);
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encoder->armed = 0;
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break;
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case 0x1:
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case 0x2:
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if (encoder->armed)
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encoder->dir = state - 1;
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break;
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case 0x3:
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encoder->armed = 1;
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break;
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}
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return IRQ_HANDLED;
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}
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static int __devinit rotary_encoder_probe(struct platform_device *pdev)
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{
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struct rotary_encoder_platform_data *pdata = pdev->dev.platform_data;
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struct rotary_encoder *encoder;
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struct input_dev *input;
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int err;
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if (!pdata || !pdata->steps) {
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dev_err(&pdev->dev, "invalid platform data\n");
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return -ENOENT;
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}
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encoder = kzalloc(sizeof(struct rotary_encoder), GFP_KERNEL);
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input = input_allocate_device();
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if (!encoder || !input) {
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dev_err(&pdev->dev, "failed to allocate memory for device\n");
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err = -ENOMEM;
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goto exit_free_mem;
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}
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encoder->input = input;
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encoder->pdata = pdata;
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encoder->irq_a = gpio_to_irq(pdata->gpio_a);
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encoder->irq_b = gpio_to_irq(pdata->gpio_b);
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/* create and register the input driver */
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input->name = pdev->name;
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input->id.bustype = BUS_HOST;
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input->dev.parent = &pdev->dev;
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input->evbit[0] = BIT_MASK(EV_ABS);
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input_set_abs_params(encoder->input,
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pdata->axis, 0, pdata->steps, 0, 1);
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err = input_register_device(input);
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if (err) {
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dev_err(&pdev->dev, "failed to register input device\n");
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goto exit_free_mem;
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}
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/* request the GPIOs */
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err = gpio_request(pdata->gpio_a, DRV_NAME);
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if (err) {
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dev_err(&pdev->dev, "unable to request GPIO %d\n",
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pdata->gpio_a);
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goto exit_unregister_input;
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}
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err = gpio_request(pdata->gpio_b, DRV_NAME);
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if (err) {
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dev_err(&pdev->dev, "unable to request GPIO %d\n",
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pdata->gpio_b);
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goto exit_free_gpio_a;
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}
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/* request the IRQs */
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err = request_irq(encoder->irq_a, &rotary_encoder_irq,
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IORESOURCE_IRQ_HIGHEDGE | IORESOURCE_IRQ_LOWEDGE,
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DRV_NAME, encoder);
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if (err) {
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dev_err(&pdev->dev, "unable to request IRQ %d\n",
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encoder->irq_a);
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goto exit_free_gpio_b;
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}
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err = request_irq(encoder->irq_b, &rotary_encoder_irq,
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IORESOURCE_IRQ_HIGHEDGE | IORESOURCE_IRQ_LOWEDGE,
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DRV_NAME, encoder);
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if (err) {
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dev_err(&pdev->dev, "unable to request IRQ %d\n",
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encoder->irq_b);
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goto exit_free_irq_a;
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}
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platform_set_drvdata(pdev, encoder);
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return 0;
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exit_free_irq_a:
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free_irq(encoder->irq_a, encoder);
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exit_free_gpio_b:
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gpio_free(pdata->gpio_b);
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exit_free_gpio_a:
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gpio_free(pdata->gpio_a);
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exit_unregister_input:
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input_unregister_device(input);
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input = NULL; /* so we don't try to free it */
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exit_free_mem:
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input_free_device(input);
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kfree(encoder);
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return err;
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}
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static int __devexit rotary_encoder_remove(struct platform_device *pdev)
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{
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struct rotary_encoder *encoder = platform_get_drvdata(pdev);
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struct rotary_encoder_platform_data *pdata = pdev->dev.platform_data;
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free_irq(encoder->irq_a, encoder);
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free_irq(encoder->irq_b, encoder);
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gpio_free(pdata->gpio_a);
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gpio_free(pdata->gpio_b);
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input_unregister_device(encoder->input);
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platform_set_drvdata(pdev, NULL);
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kfree(encoder);
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return 0;
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}
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static struct platform_driver rotary_encoder_driver = {
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.probe = rotary_encoder_probe,
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.remove = __devexit_p(rotary_encoder_remove),
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.driver = {
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.name = DRV_NAME,
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.owner = THIS_MODULE,
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}
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};
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static int __init rotary_encoder_init(void)
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{
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return platform_driver_register(&rotary_encoder_driver);
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}
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static void __exit rotary_encoder_exit(void)
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{
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platform_driver_unregister(&rotary_encoder_driver);
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}
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module_init(rotary_encoder_init);
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module_exit(rotary_encoder_exit);
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MODULE_ALIAS("platform:" DRV_NAME);
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MODULE_DESCRIPTION("GPIO rotary encoder driver");
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MODULE_AUTHOR("Daniel Mack <daniel@caiaq.de>");
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MODULE_LICENSE("GPL v2");
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13
include/linux/rotary_encoder.h
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13
include/linux/rotary_encoder.h
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@ -0,0 +1,13 @@
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#ifndef __ROTARY_ENCODER_H__
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#define __ROTARY_ENCODER_H__
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struct rotary_encoder_platform_data {
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unsigned int steps;
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unsigned int axis;
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unsigned int gpio_a;
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unsigned int gpio_b;
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unsigned int inverted_a;
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unsigned int inverted_b;
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};
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#endif /* __ROTARY_ENCODER_H__ */
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