input: keyboard: Add Fast GPIO-driven keyboard/keypad matrix driver

This driver is a reimplementation of matrix_keyboard, on which it
is heavily based: the former was made back in 2009 and then
lightly updated in 2012 to add some support for device-tree / OF.

It turns out that this is not enough, nor OF is fully supported,
as the global (or "clustered") interrupt is never probed, nor it
made usage of the GPIOD API which, nowadays, really simplifies
the job - but not only: it also provides means to set GPIO arrays
for controllers that are supporting this.
The latter is very important when dealing with slow GPIOs such as
I2C and/or SPI expanders (and, again, not only); by using the new
APIs everything fits the new systems, from simplifications of the
probe/remove functions to opening possibility of using expanders
to drive key matrices with or without protection diodes.

But then, why wasn't the old matrix_keyboard driver modified
instead of creating a new one?
The problem there is that the old driver is made to support the
old platform_device style and it's currently still being used by
some PXA boards that are not (yet?) ported to device-tree, so it
would be impossible to modernize it for good, which means that to
support GPIOD (which is - really - required for the aforementioned
reasons) and to fully support DT it would be necessary to wrap the
old GPIO API around the new GPIOD one, creating overhead and also
probably unnecessary memory usage, other than a very big driver
which, at least on embedded devices (having limited resources),
would be simply bad. Leaving the fact that I haven't got any old
board so it's impossible for me to analyze and optimize for them.

Since 98% of the users of the old driver are infact platforms that
have been ported to (or are born with) DT, the introduction of a
new driver that's purely made for them seemed to be the best
choice, also because the expectations are (I think) that all of
the old ARM-based boards will be ported to DT anyway, which will
actually deprecate the good old matrix_keyboard driver.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>

drivers/input/keyboard/Kconfig

@@ -246,6 +246,19 @@ config KEYBOARD_GPIO
 	  To compile this driver as a module, choose M here: the
 	  module will be called gpio_keys.
 
+config KEYBOARD_GPIO_FASTMATRIX
+	tristate "GPIO Keyboard"
+	depends on GPIOLIB
+	select INPUT_MATRIXKMAP
+	help
+	  This driver implements support for matrix keypads and/or
+	  keyboards connected directly to GPIO pins of a CPU, made
+	  to also perform with slow I2C GPIO expanders and even
+	  on matrices with no protection diodes.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called gpio_fastmatrix
+
 config KEYBOARD_GPIO_POLLED
 	tristate "Polled GPIO buttons"
 	depends on GPIOLIB

drivers/input/keyboard/Makefile

@@ -23,6 +23,7 @@ obj-$(CONFIG_KEYBOARD_DLINK_DIR685)	+= dlink-dir685-touchkeys.o
 obj-$(CONFIG_KEYBOARD_EP93XX)		+= ep93xx_keypad.o
 obj-$(CONFIG_KEYBOARD_GOLDFISH_EVENTS)	+= goldfish_events.o
 obj-$(CONFIG_KEYBOARD_GPIO)		+= gpio_keys.o
+obj-$(CONFIG_KEYBOARD_GPIO_FASTMATRIX)	+= gpio_fastmatrix.o
 obj-$(CONFIG_KEYBOARD_GPIO_POLLED)	+= gpio_keys_polled.o
 obj-$(CONFIG_KEYBOARD_TCA6416)		+= tca6416-keypad.o
 obj-$(CONFIG_KEYBOARD_TCA8418)		+= tca8418_keypad.o

drivers/input/keyboard/gpio_fastmatrix.c

@@ -0,0 +1,528 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Fast GPIO driven keyboard/keypad matrix driver
+ *
+ *  Copyright (c) 2020 AngeloGioacchino Del Regno
+ *                     <angelogioacchino.delregno@somainline.org>
+ *  Based on matrix_keypad.c
+ */
+
+#include <linux/types.h>
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+#include <linux/input.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/gpio.h>
+#include <linux/input/matrix_keypad.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_gpio.h>
+#include <linux/of_platform.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+
+struct gpio_keyboard {
+	struct device *dev;
+	struct input_dev *input_dev;
+	unsigned int row_shift;
+
+	struct gpio_descs *row_gpios;
+	struct gpio_descs *col_gpios;
+	u32 autorescan_ms;
+	u32 debounce_ms;
+	u32 col_scan_us;
+	int clustered_irq;
+
+	DECLARE_BITMAP(disabled_gpios, MATRIX_MAX_ROWS);
+
+	u32 last_key_state[MATRIX_MAX_COLS];
+	struct delayed_work work;
+	struct mutex lock;
+
+	bool drive_inactive_cols;
+	bool gpio_all_disabled;
+	bool scan_pending;
+	bool stopped;
+};
+
+static int activate_one_column(struct gpio_keyboard *gkb, int col, bool wait)
+{
+	int ret;
+
+	ret = gpiod_direction_output(gkb->col_gpios->desc[col], 1);
+	if (ret)
+		return ret;
+	if (wait && gkb->col_scan_us)
+		udelay(gkb->col_scan_us);
+	return 0;
+}
+
+/*
+ * NOTE: If drive_inactive_cols is false, then the GPIO has to be put into
+ * HiZ when de-activated to cause minmal side effect when scanning other
+ * columns. In that case it is configured here to be input, otherwise it is
+ * driven with the inactive value.
+ */
+static int deactivate_one_column(struct gpio_keyboard *gkb, int col)
+{
+	gpiod_set_value_cansleep(gkb->col_gpios->desc[col], 0);
+	if (!gkb->drive_inactive_cols)
+		return gpiod_direction_input(gkb->col_gpios->desc[col]);
+	return 0;
+}
+
+static int activate_all_cols(struct gpio_keyboard *gkb)
+{
+	unsigned long val = ULONG_MAX;
+	int ret, col;
+
+	/*
+	 * Shortcut! If we don't have to set direction, we can use
+	 * the way faster gpiod array setting instead.
+	 */
+	if (gkb->drive_inactive_cols) {
+		return gpiod_set_array_value_cansleep(gkb->col_gpios->ndescs,
+						      gkb->col_gpios->desc,
+						      gkb->col_gpios->info,
+						      &val);
+	}
+
+	for (col = 0; col < gkb->col_gpios->ndescs; col++) {
+		ret = activate_one_column(gkb, col, false);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int deactivate_all_cols(struct gpio_keyboard *gkb)
+{
+	unsigned long val = 0;
+	int col, ret;
+
+	/*
+	 * If the GPIO controller supports setting all pins at once it
+	 * is going to be way faster, otherwise this function will fall
+	 * back to setting all pins one at a time.
+	 */
+	ret = gpiod_set_array_value_cansleep(gkb->col_gpios->ndescs,
+					     gkb->col_gpios->desc,
+					     gkb->col_gpios->info, &val);
+	if (ret)
+		return ret;
+
+	if (!gkb->drive_inactive_cols) {
+		for (col = 0; col < gkb->col_gpios->ndescs; col++)
+			gpiod_direction_input(gkb->col_gpios->desc[col]);
+	}
+	return ret;
+}
+
+static void enable_row_irqs(struct gpio_keyboard *gkb)
+{
+	int i;
+
+	if (gkb->clustered_irq > 0)
+		enable_irq(gkb->clustered_irq);
+	else {
+		for (i = 0; i < gkb->row_gpios->ndescs; i++)
+			enable_irq(gpiod_to_irq(gkb->row_gpios->desc[i]));
+	}
+}
+
+static void disable_row_irqs(struct gpio_keyboard *gkb)
+{
+	int i;
+
+	if (gkb->clustered_irq > 0)
+		disable_irq_nosync(gkb->clustered_irq);
+	else {
+		for (i = 0; i < gkb->row_gpios->ndescs; i++)
+			disable_irq_nosync(gpiod_to_irq(gkb->row_gpios->desc[i]));
+	}
+}
+
+/*
+ * This gets the keys from keyboard and reports it to input subsystem
+ */
+static void gpio_keyboard_scan(struct work_struct *work)
+{
+	struct gpio_keyboard *gkb =
+		container_of(work, struct gpio_keyboard, work.work);
+	struct input_dev *input_dev = gkb->input_dev;
+	const unsigned short *keycodes = input_dev->keycode;
+	u32 *new_state;
+	unsigned long row_values;
+	int ret, row, col, code;
+	u32 keymask = 0;
+
+	new_state = kzalloc(gkb->col_gpios->ndescs * sizeof(*new_state),
+			    GFP_KERNEL);
+	if (!new_state)
+		return;
+
+	/* de-activate all columns for scanning */
+	deactivate_all_cols(gkb);
+
+	/* assert each column and read the row status out */
+	for (col = 0; col < gkb->col_gpios->ndescs; col++) {
+		activate_one_column(gkb, col, true);
+
+		ret = gpiod_get_array_value_cansleep(gkb->row_gpios->ndescs,
+						     gkb->row_gpios->desc,
+						     gkb->row_gpios->info,
+						     &row_values);
+		new_state[col] = row_values;
+		keymask |= new_state[col];
+
+		if (deactivate_one_column(gkb, col)) {
+			activate_all_cols(gkb);
+			goto end;
+		}
+	}
+
+	activate_all_cols(gkb);
+
+	for (col = 0; col < gkb->col_gpios->ndescs; col++) {
+		u32 bits_changed = gkb->last_key_state[col] ^ new_state[col];
+		if (bits_changed == 0)
+			continue;
+
+		for (row = 0; bits_changed; row++, bits_changed >>=1 ) {
+			if (!(bits_changed & BIT(0)))
+				continue;
+
+			code = MATRIX_SCAN_CODE(row, col, gkb->row_shift);
+			input_event(input_dev, EV_MSC, MSC_SCAN, code);
+			input_report_key(input_dev, keycodes[code],
+					 new_state[col] & (1 << row));
+		}
+	}
+	input_sync(input_dev);
+
+	memcpy(gkb->last_key_state, new_state, sizeof(gkb->last_key_state));
+	kfree(new_state);
+
+	/* Avoid missing key release events on quirky hardware */
+	if (gkb->autorescan_ms && keymask) {
+		queue_delayed_work(system_highpri_wq, &gkb->work,
+				   msecs_to_jiffies(gkb->autorescan_ms));
+		return;
+	}
+end:
+	/* Enable IRQs again */
+	mutex_lock(&gkb->lock);
+	gkb->scan_pending = false;
+	enable_row_irqs(gkb);
+	mutex_unlock(&gkb->lock);
+}
+
+static irqreturn_t gpio_keyboard_interrupt(int irq, void *id)
+{
+	struct gpio_keyboard *gkb = id;
+
+	/*
+	 * See if another IRQ beaten us to it and scheduled the
+	 * scan already. In that case we should not try to
+	 * disable IRQs again.
+	 */
+	if (unlikely(gkb->scan_pending || gkb->stopped))
+		goto out;
+
+	mutex_lock(&gkb->lock);
+
+	disable_row_irqs(gkb);
+	gkb->scan_pending = true;
+	mod_delayed_work(system_highpri_wq, &gkb->work,
+			 msecs_to_jiffies(gkb->debounce_ms));
+
+out:
+	mutex_unlock(&gkb->lock);
+	return IRQ_HANDLED;
+}
+
+static int gpio_keyboard_start(struct input_dev *dev)
+{
+	struct gpio_keyboard *gkb = input_get_drvdata(dev);
+
+	gkb->stopped = false;
+
+	/*
+	 * Schedule an immediate key scan to capture current key state;
+	 * columns will be activated and IRQs be enabled after the scan.
+	 */
+	schedule_delayed_work(&gkb->work, 0);
+
+	return 0;
+}
+
+static void gpio_keyboard_stop(struct input_dev *dev)
+{
+	struct gpio_keyboard *gkb = input_get_drvdata(dev);
+
+	mutex_lock(&gkb->lock);
+	gkb->stopped = true;
+	mutex_unlock(&gkb->lock);
+
+	flush_delayed_work(&gkb->work);
+	/*
+	 * gpio_keyboard_scan() will leave IRQs enabled;
+	 * we should disable them now.
+	 */
+	disable_row_irqs(gkb);
+}
+
+static void __maybe_unused gpio_keyboard_wakeup_en(struct gpio_keyboard *gkb)
+{
+	int irq, i;
+
+	if (gkb->clustered_irq > 0) {
+		if (enable_irq_wake(gkb->clustered_irq) == 0)
+			gkb->gpio_all_disabled = true;
+	} else {
+
+		for (i = 0; i < gkb->row_gpios->ndescs; i++) {
+			if (!test_bit(i, gkb->disabled_gpios)) {
+				irq = gpiod_to_irq(gkb->row_gpios->desc[i]);
+
+				if (enable_irq_wake(irq) == 0)
+					__set_bit(i, gkb->disabled_gpios);
+			}
+		}
+	}
+}
+
+static void __maybe_unused gpio_keyboard_wakeup_dis(struct gpio_keyboard *gkb)
+{
+	int irq, i;
+
+	if (gkb->clustered_irq > 0) {
+		if (gkb->gpio_all_disabled) {
+			disable_irq_wake(gkb->clustered_irq);
+			gkb->gpio_all_disabled = false;
+		}
+	} else {
+		for (i = 0; i < gkb->row_gpios->ndescs; i++) {
+			if (test_and_clear_bit(i, gkb->disabled_gpios)) {
+				irq = gpiod_to_irq(gkb->row_gpios->desc[i]);
+				disable_irq_wake(irq);
+			}
+		}
+	}
+}
+
+static int __maybe_unused gpio_keyboard_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct gpio_keyboard *gkb = platform_get_drvdata(pdev);
+
+	gpio_keyboard_stop(gkb->input_dev);
+
+	if (device_may_wakeup(&pdev->dev))
+		gpio_keyboard_wakeup_en(gkb);
+
+	return 0;
+}
+
+static int __maybe_unused gpio_keyboard_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct gpio_keyboard *gkb = platform_get_drvdata(pdev);
+
+	if (device_may_wakeup(&pdev->dev))
+		gpio_keyboard_wakeup_dis(gkb);
+
+	gpio_keyboard_start(gkb->input_dev);
+
+	return 0;
+}
+static SIMPLE_DEV_PM_OPS(gpio_keyboard_pm_ops,
+			 gpio_keyboard_suspend, gpio_keyboard_resume);
+
+static int gpio_keyboard_init_gpio(struct platform_device *pdev,
+				   struct gpio_keyboard *gkb)
+{
+	int i, ret;
+
+	if (gkb->clustered_irq > 0) {
+		ret = devm_request_threaded_irq(gkb->dev, gkb->clustered_irq,
+						NULL, gpio_keyboard_interrupt,
+						IRQF_ONESHOT, "gpio-keyboard", gkb);
+		if (ret < 0) {
+			dev_err(&pdev->dev,
+				"Cannot get IRQ %d\n", gkb->clustered_irq);
+			return ret;
+		}
+	} else {
+		for (i = 0; i < gkb->row_gpios->ndescs; i++) {
+			ret = devm_request_threaded_irq(
+					gkb->dev,
+					gpiod_to_irq(gkb->row_gpios->desc[i]),
+					NULL, gpio_keyboard_interrupt,
+					IRQF_TRIGGER_HIGH |
+					IRQF_TRIGGER_LOW,
+					"gpio-keyboard", gkb);
+			if (ret < 0) {
+				dev_err(&pdev->dev,
+					"Cannot get IRQ for gpio%d\n",
+					desc_to_gpio(gkb->row_gpios->desc[i]));
+				return ret;
+			}
+		}
+	}
+
+	/* initialized as disabled - enabled by input->open */
+	disable_row_irqs(gkb);
+	return 0;
+}
+
+static int gpio_keyboard_parse_dt(struct gpio_keyboard *gkb)
+{
+	struct device *dev = gkb->dev;
+	int rc;
+
+	/*
+	 * Get as GPIOD_ASIS to use the configuration that comes from
+	 * device-tree. Anyway, in many cases the row is configured as
+	 * input, while the column is configured as output-high.
+	 *
+	 * This may vary depending on the hardware.
+	 */
+	gkb->row_gpios = devm_gpiod_get_array(dev, "row", GPIOD_ASIS);
+	if (IS_ERR(gkb->row_gpios))
+		return PTR_ERR(gkb->row_gpios);
+
+	gkb->col_gpios = devm_gpiod_get_array(dev, "col", GPIOD_ASIS);
+	if (IS_ERR(gkb->col_gpios))
+		return PTR_ERR(gkb->col_gpios);
+
+	/* All of these additional properties are optional */
+	device_property_read_string(dev, "label", &gkb->input_dev->name);
+
+	if (device_property_read_bool(dev, "autorepeat"))
+		__set_bit(EV_REP, gkb->input_dev->evbit);
+
+	gkb->drive_inactive_cols =
+		device_property_read_bool(dev, "drive-inactive-cols");
+
+	rc = device_property_read_u32(dev, "autorescan-ms",
+				      &gkb->autorescan_ms);
+	if (rc < 0)
+		gkb->autorescan_ms = 0;
+
+	rc = device_property_read_u32(dev, "debounce-delay-ms",
+				      &gkb->debounce_ms);
+	if (rc < 0)
+		gkb->debounce_ms = 0;
+
+	rc = device_property_read_u32(dev, "col-scan-delay-us",
+				      &gkb->col_scan_us);
+	if (rc < 0)
+		gkb->col_scan_us = 0;
+
+	return 0;
+}
+
+static int gpio_keyboard_probe(struct platform_device *pdev)
+{
+	struct gpio_keyboard *gkb;
+	bool wake;
+	int irq, ret;
+
+	gkb = devm_kmalloc(&pdev->dev, sizeof(*gkb), GFP_KERNEL);
+	if (!gkb)
+		return -ENOMEM;
+
+	gkb->dev = &pdev->dev;
+	gkb->input_dev = devm_input_allocate_device(&pdev->dev);
+	if (!gkb->input_dev)
+		return -ENOMEM;
+
+	ret = gpio_keyboard_parse_dt(gkb);
+	if (ret)
+		return ret;
+
+	irq = platform_get_irq_optional(pdev, 0);
+	gkb->clustered_irq = (irq > 0) ? irq : 0;
+	gkb->row_shift = get_count_order(gkb->col_gpios->ndescs);
+	gkb->stopped = true;
+	INIT_DELAYED_WORK(&gkb->work, gpio_keyboard_scan);
+	memset(gkb->last_key_state, 0, sizeof(gkb->last_key_state));
+	mutex_init(&gkb->lock);
+
+	if (!gkb->input_dev->name)
+		gkb->input_dev->name = pdev->name;
+	gkb->input_dev->id.bustype = BUS_HOST;
+	gkb->input_dev->dev.parent = &pdev->dev;
+	gkb->input_dev->open = gpio_keyboard_start;
+	gkb->input_dev->close = gpio_keyboard_stop;
+
+	ret = matrix_keypad_build_keymap(NULL, NULL,
+					 gkb->row_gpios->ndescs,
+					 gkb->col_gpios->ndescs,
+					 NULL, gkb->input_dev);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to build keymap\n");
+		return ret;
+	}
+
+	input_set_capability(gkb->input_dev, EV_MSC, MSC_SCAN);
+	input_set_drvdata(gkb->input_dev, gkb);
+
+	ret = gpio_keyboard_init_gpio(pdev, gkb);
+	if (ret)
+		return ret;
+
+	ret = input_register_device(gkb->input_dev);
+	if (ret)
+		return ret;
+
+	wake = device_property_read_bool(&pdev->dev, "wakeup-source");
+	device_init_wakeup(&pdev->dev, wake);
+
+	platform_set_drvdata(pdev, gkb);
+
+	return 0;
+}
+
+static int gpio_keyboard_remove(struct platform_device *pdev)
+{
+	struct gpio_keyboard *gkb = platform_get_drvdata(pdev);
+	int i;
+
+	if (gkb->clustered_irq > 0) {
+		free_irq(gkb->clustered_irq, gkb);
+	} else {
+		for (i = 0; i < gkb->row_gpios->ndescs; i++)
+			free_irq(gpiod_to_irq(gkb->row_gpios->desc[i]), gkb);
+	}
+	input_unregister_device(gkb->input_dev);
+
+	return 0;
+}
+
+static const struct of_device_id gpio_keyboard_dt_match[] = {
+	{ .compatible = "gpio-fastmatrix-keyboard" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, gpio_keyboard_dt_match);
+
+static struct platform_driver gpio_keyboard_driver = {
+	.probe		= gpio_keyboard_probe,
+	.remove		= gpio_keyboard_remove,
+	.driver		= {
+		.name	= "gpio-fastmatrix-keyboard",
+		.pm	= &gpio_keyboard_pm_ops,
+		.of_match_table = gpio_keyboard_dt_match,
+	},
+};
+module_platform_driver(gpio_keyboard_driver);
+
+MODULE_AUTHOR("AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>");
+MODULE_DESCRIPTION("Fast GPIO driven keyboard/keypad matrix driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:gpio-fastmatrix-keyboard");