Input: add ADC resistor ladder driver

A common way of multiplexing buttons on a single input in cheap devices is
to use a resistor ladder on an ADC. This driver supports that configuration
by polling an ADC channel provided by IIO.

Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

3 files changed, 226 insertions, 0 deletions

diff --git a/drivers/input/keyboard/Kconfig b/drivers/input/keyboard/Kconfig
index 509608c95994..cbd75cf44739 100644
--- a/drivers/input/keyboard/Kconfig
+++ b/drivers/input/keyboard/Kconfig
@@ -12,6 +12,21 @@ menuconfig INPUT_KEYBOARD
 
 if INPUT_KEYBOARD
 
+config KEYBOARD_ADC
+        tristate "ADC Ladder Buttons"
+        depends on IIO
+        select INPUT_POLLDEV
+        help
+          This driver implements support for buttons connected
+          to an ADC using a resistor ladder.
+
+          Say Y here if your device has such buttons connected to an ADC.  Your
+          board-specific setup logic must also provide a configuration data
+          for mapping voltages to buttons.
+
+          To compile this driver as a module, choose M here: the
+          module will be called adc_keys.
+
 config KEYBOARD_ADP5520
         tristate "Keypad Support for ADP5520 PMIC"
         depends on PMIC_ADP5520
diff --git a/drivers/input/keyboard/Makefile b/drivers/input/keyboard/Makefile
index 1d416ddf84e4..d9f4cfcf3410 100644
--- a/drivers/input/keyboard/Makefile
+++ b/drivers/input/keyboard/Makefile
@@ -4,6 +4,7 @@
 
 # Each configuration option enables a list of files.
 
+obj-$(CONFIG_KEYBOARD_ADC)              += adc-keys.o
 obj-$(CONFIG_KEYBOARD_ADP5520)          += adp5520-keys.o
 obj-$(CONFIG_KEYBOARD_ADP5588)          += adp5588-keys.o
 obj-$(CONFIG_KEYBOARD_ADP5589)          += adp5589-keys.o
diff --git a/drivers/input/keyboard/adc-keys.c b/drivers/input/keyboard/adc-keys.c
new file mode 100644
index 000000000000..f8cf2ccacefd
--- /dev/null
+++ b/drivers/input/keyboard/adc-keys.c
@@ -0,0 +1,210 @@
+/*
+ * Input driver for resistor ladder connected on ADC
+ *
+ * Copyright (c) 2016 Alexandre Belloni
+ *
+ * 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/err.h>
+#include <linux/iio/consumer.h>
+#include <linux/iio/types.h>
+#include <linux/input.h>
+#include <linux/input-polldev.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+struct adc_keys_button {
+        u32 voltage;
+        u32 keycode;
+};
+
+struct adc_keys_state {
+        struct iio_channel *channel;
+        u32 num_keys;
+        u32 last_key;
+        u32 keyup_voltage;
+        const struct adc_keys_button *map;
+};
+
+static void adc_keys_poll(struct input_polled_dev *dev)
+{
+        struct adc_keys_state *st = dev->private;
+        int i, value, ret;
+        u32 diff, closest = 0xffffffff;
+        int keycode = 0;
+
+        ret = iio_read_channel_processed(st->channel, &value);
+        if (unlikely(ret < 0)) {
+                /* Forcibly release key if any was pressed */
+                value = st->keyup_voltage;
+        } else {
+                for (i = 0; i < st->num_keys; i++) {
+                        diff = abs(st->map[i].voltage - value);
+                        if (diff < closest) {
+                                closest = diff;
+                                keycode = st->map[i].keycode;
+                        }
+                }
+        }
+
+        if (abs(st->keyup_voltage - value) < closest)
+                keycode = 0;
+
+        if (st->last_key && st->last_key != keycode)
+                input_report_key(dev->input, st->last_key, 0);
+
+        if (keycode)
+                input_report_key(dev->input, keycode, 1);
+
+        input_sync(dev->input);
+        st->last_key = keycode;
+}
+
+static int adc_keys_load_keymap(struct device *dev, struct adc_keys_state *st)
+{
+        struct adc_keys_button *map;
+        struct fwnode_handle *child;
+        int i;
+
+        st->num_keys = device_get_child_node_count(dev);
+        if (st->num_keys == 0) {
+                dev_err(dev, "keymap is missing\n");
+                return -EINVAL;
+        }
+
+        map = devm_kmalloc_array(dev, st->num_keys, sizeof(*map), GFP_KERNEL);
+        if (!map)
+                return -ENOMEM;
+
+        i = 0;
+        device_for_each_child_node(dev, child) {
+                if (fwnode_property_read_u32(child, "press-threshold-microvolt",
+                                             &map[i].voltage)) {
+                        dev_err(dev, "Key with invalid or missing voltage\n");
+                        fwnode_handle_put(child);
+                        return -EINVAL;
+                }
+                map[i].voltage /= 1000;
+
+                if (fwnode_property_read_u32(child, "linux,code",
+                                             &map[i].keycode)) {
+                        dev_err(dev, "Key with invalid or missing linux,code\n");
+                        fwnode_handle_put(child);
+                        return -EINVAL;
+                }
+
+                i++;
+        }
+
+        st->map = map;
+        return 0;
+}
+
+static int adc_keys_probe(struct platform_device *pdev)
+{
+        struct device *dev = &pdev->dev;
+        struct adc_keys_state *st;
+        struct input_polled_dev *poll_dev;
+        struct input_dev *input;
+        enum iio_chan_type type;
+        int i, value;
+        int error;
+
+        st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
+        if (!st)
+                return -ENOMEM;
+
+        st->channel = devm_iio_channel_get(dev, "buttons");
+        if (IS_ERR(st->channel))
+                return PTR_ERR(st->channel);
+
+        if (!st->channel->indio_dev)
+                return -ENXIO;
+
+        error = iio_get_channel_type(st->channel, &type);
+        if (error < 0)
+                return error;
+
+        if (type != IIO_VOLTAGE) {
+                dev_err(dev, "Incompatible channel type %d\n", type);
+                return -EINVAL;
+        }
+
+        if (device_property_read_u32(dev, "keyup-threshold-microvolt",
+                                     &st->keyup_voltage)) {
+                dev_err(dev, "Invalid or missing keyup voltage\n");
+                return -EINVAL;
+        }
+        st->keyup_voltage /= 1000;
+
+        error = adc_keys_load_keymap(dev, st);
+        if (error)
+                return error;
+
+        platform_set_drvdata(pdev, st);
+
+        poll_dev = devm_input_allocate_polled_device(dev);
+        if (!poll_dev) {
+                dev_err(dev, "failed to allocate input device\n");
+                return -ENOMEM;
+        }
+
+        if (!device_property_read_u32(dev, "poll-interval", &value))
+                poll_dev->poll_interval = value;
+
+        poll_dev->poll = adc_keys_poll;
+        poll_dev->private = st;
+
+        input = poll_dev->input;
+
+        input->name = pdev->name;
+        input->phys = "adc-keys/input0";
+
+        input->id.bustype = BUS_HOST;
+        input->id.vendor = 0x0001;
+        input->id.product = 0x0001;
+        input->id.version = 0x0100;
+
+        __set_bit(EV_KEY, input->evbit);
+        for (i = 0; i < st->num_keys; i++)
+                __set_bit(st->map[i].keycode, input->keybit);
+
+        if (device_property_read_bool(dev, "autorepeat"))
+                __set_bit(EV_REP, input->evbit);
+
+        error = input_register_polled_device(poll_dev);
+        if (error) {
+                dev_err(dev, "Unable to register input device: %d\n", error);
+                return error;
+        }
+
+        return 0;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id adc_keys_of_match[] = {
+        { .compatible = "adc-keys", },
+        { }
+};
+MODULE_DEVICE_TABLE(of, adc_keys_of_match);
+#endif
+
+static struct platform_driver __refdata adc_keys_driver = {
+        .driver = {
+                .name = "adc_keys",
+                .of_match_table = of_match_ptr(adc_keys_of_match),
+        },
+        .probe = adc_keys_probe,
+};
+module_platform_driver(adc_keys_driver);
+
+MODULE_AUTHOR("Alexandre Belloni <alexandre.belloni@free-electrons.com>");
+MODULE_DESCRIPTION("Input driver for resistor ladder connected on ADC");
+MODULE_LICENSE("GPL v2");