auxdisplay: Add HD44780 Character LCD support

The Hitachi HD44780 Character LCD Controller is commonly used on
character LCDs that can display one or more lines of text.

This driver supports character LCDs connected to GPIOs, using either a
4-bit or 8-bit data bus, and provides access through the charlcd core
and /dev/lcd.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/auxdisplay/Kconfig

@@ -18,6 +18,17 @@ config CHARLCD
 
 if AUXDISPLAY
 
+config HD44780
+	tristate "HD44780 Character LCD support"
+	depends on GPIOLIB || COMPILE_TEST
+	select CHARLCD
+	---help---
+	  Enable support for Character LCDs using a HD44780 controller.
+	  The LCD is accessible through the /dev/lcd char device (10, 156).
+	  This code can either be compiled as a module, or linked into the
+	  kernel and started at boot.
+	  If you don't understand what all this is about, say N.
+
 config KS0108
 	tristate "KS0108 LCD Controller"
 	depends on PARPORT_PC

drivers/auxdisplay/Makefile

@@ -6,4 +6,5 @@ obj-$(CONFIG_CHARLCD)		+= charlcd.o
 obj-$(CONFIG_KS0108)		+= ks0108.o
 obj-$(CONFIG_CFAG12864B)	+= cfag12864b.o cfag12864bfb.o
 obj-$(CONFIG_IMG_ASCII_LCD)	+= img-ascii-lcd.o
+obj-$(CONFIG_HD44780)		+= hd44780.o
 obj-$(CONFIG_HT16K33)		+= ht16k33.o

drivers/auxdisplay/hd44780.c

+/*
+ * HD44780 Character LCD driver for Linux
+ *
+ * Copyright (C) 2000-2008, Willy Tarreau <w@1wt.eu>
+ * Copyright (C) 2016-2017 Glider bvba
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+#include <misc/charlcd.h>
+
+
+enum hd44780_pin {
+	/* Order does matter due to writing to GPIO array subsets! */
+	PIN_DATA0,	/* Optional */
+	PIN_DATA1,	/* Optional */
+	PIN_DATA2,	/* Optional */
+	PIN_DATA3,	/* Optional */
+	PIN_DATA4,
+	PIN_DATA5,
+	PIN_DATA6,
+	PIN_DATA7,
+	PIN_CTRL_RS,
+	PIN_CTRL_RW,	/* Optional */
+	PIN_CTRL_E,
+	PIN_CTRL_BL,   /* Optional */
+	PIN_NUM
+};
+
+struct hd44780 {
+	struct gpio_desc *pins[PIN_NUM];
+};
+
+static void hd44780_backlight(struct charlcd *lcd, int on)
+{
+	struct hd44780 *hd = lcd->drvdata;
+
+	if (hd->pins[PIN_CTRL_BL])
+		gpiod_set_value_cansleep(hd->pins[PIN_CTRL_BL], on);
+}
+
+static void hd44780_strobe_gpio(struct hd44780 *hd)
+{
+	/* Maintain the data during 20 us before the strobe */
+	udelay(20);
+
+	gpiod_set_value_cansleep(hd->pins[PIN_CTRL_E], 1);
+
+	/* Maintain the strobe during 40 us */
+	udelay(40);
+
+	gpiod_set_value_cansleep(hd->pins[PIN_CTRL_E], 0);
+}
+
+/* write to an LCD panel register in 8 bit GPIO mode */
+static void hd44780_write_gpio8(struct hd44780 *hd, u8 val, unsigned int rs)
+{
+	int values[10];	/* for DATA[0-7], RS, RW */
+	unsigned int i, n;
+
+	for (i = 0; i < 8; i++)
+		values[PIN_DATA0 + i] = !!(val & BIT(i));
+	values[PIN_CTRL_RS] = rs;
+	n = 9;
+	if (hd->pins[PIN_CTRL_RW]) {
+		values[PIN_CTRL_RW] = 0;
+		n++;
+	}
+
+	/* Present the data to the port */
+	gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA0], values);
+
+	hd44780_strobe_gpio(hd);
+}
+
+/* write to an LCD panel register in 4 bit GPIO mode */
+static void hd44780_write_gpio4(struct hd44780 *hd, u8 val, unsigned int rs)
+{
+	int values[10];	/* for DATA[0-7], RS, RW, but DATA[0-3] is unused */
+	unsigned int i, n;
+
+	/* High nibble + RS, RW */
+	for (i = 4; i < 8; i++)
+		values[PIN_DATA0 + i] = !!(val & BIT(i));
+	values[PIN_CTRL_RS] = rs;
+	n = 5;
+	if (hd->pins[PIN_CTRL_RW]) {
+		values[PIN_CTRL_RW] = 0;
+		n++;
+	}
+
+	/* Present the data to the port */
+	gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4],
+				       &values[PIN_DATA4]);
+
+	hd44780_strobe_gpio(hd);
+
+	/* Low nibble */
+	for (i = 0; i < 4; i++)
+		values[PIN_DATA4 + i] = !!(val & BIT(i));
+
+	/* Present the data to the port */
+	gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4],
+				       &values[PIN_DATA4]);
+
+	hd44780_strobe_gpio(hd);
+}
+
+/* Send a command to the LCD panel in 8 bit GPIO mode */
+static void hd44780_write_cmd_gpio8(struct charlcd *lcd, int cmd)
+{
+	struct hd44780 *hd = lcd->drvdata;
+
+	hd44780_write_gpio8(hd, cmd, 0);
+
+	/* The shortest command takes at least 120 us */
+	udelay(120);
+}
+
+/* Send data to the LCD panel in 8 bit GPIO mode */
+static void hd44780_write_data_gpio8(struct charlcd *lcd, int data)
+{
+	struct hd44780 *hd = lcd->drvdata;
+
+	hd44780_write_gpio8(hd, data, 1);
+
+	/* The shortest data takes at least 45 us */
+	udelay(45);
+}
+
+static const struct charlcd_ops hd44780_ops_gpio8 = {
+	.write_cmd	= hd44780_write_cmd_gpio8,
+	.write_data	= hd44780_write_data_gpio8,
+	.backlight	= hd44780_backlight,
+};
+
+/* Send a command to the LCD panel in 4 bit GPIO mode */
+static void hd44780_write_cmd_gpio4(struct charlcd *lcd, int cmd)
+{
+	struct hd44780 *hd = lcd->drvdata;
+
+	hd44780_write_gpio4(hd, cmd, 0);
+
+	/* The shortest command takes at least 120 us */
+	udelay(120);
+}
+
+/* Send 4-bits of a command to the LCD panel in raw 4 bit GPIO mode */
+static void hd44780_write_cmd_raw_gpio4(struct charlcd *lcd, int cmd)
+{
+	int values[10];	/* for DATA[0-7], RS, RW, but DATA[0-3] is unused */
+	struct hd44780 *hd = lcd->drvdata;
+	unsigned int i, n;
+
+	/* Command nibble + RS, RW */
+	for (i = 0; i < 4; i++)
+		values[PIN_DATA4 + i] = !!(cmd & BIT(i));
+	values[PIN_CTRL_RS] = 0;
+	n = 5;
+	if (hd->pins[PIN_CTRL_RW]) {
+		values[PIN_CTRL_RW] = 0;
+		n++;
+	}
+
+	/* Present the data to the port */
+	gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4],
+				       &values[PIN_DATA4]);
+
+	hd44780_strobe_gpio(hd);
+}
+
+/* Send data to the LCD panel in 4 bit GPIO mode */
+static void hd44780_write_data_gpio4(struct charlcd *lcd, int data)
+{
+	struct hd44780 *hd = lcd->drvdata;
+
+	hd44780_write_gpio4(hd, data, 1);
+
+	/* The shortest data takes at least 45 us */
+	udelay(45);
+}
+
+static const struct charlcd_ops hd44780_ops_gpio4 = {
+	.write_cmd	= hd44780_write_cmd_gpio4,
+	.write_cmd_raw4	= hd44780_write_cmd_raw_gpio4,
+	.write_data	= hd44780_write_data_gpio4,
+	.backlight	= hd44780_backlight,
+};
+
+static int hd44780_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	unsigned int i, base;
+	struct charlcd *lcd;
+	struct hd44780 *hd;
+	int ifwidth, ret;
+
+	/* Required pins */
+	ifwidth = gpiod_count(dev, "data");
+	if (ifwidth < 0)
+		return ifwidth;
+
+	switch (ifwidth) {
+	case 4:
+		base = PIN_DATA4;
+		break;
+	case 8:
+		base = PIN_DATA0;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	lcd = charlcd_alloc(sizeof(struct hd44780));
+	if (!lcd)
+		return -ENOMEM;
+
+	hd = lcd->drvdata;
+
+	for (i = 0; i < ifwidth; i++) {
+		hd->pins[base + i] = devm_gpiod_get_index(dev, "data", i,
+							  GPIOD_OUT_LOW);
+		if (IS_ERR(hd->pins[base + i])) {
+			ret = PTR_ERR(hd->pins[base + i]);
+			goto fail;
+		}
+	}
+
+	hd->pins[PIN_CTRL_E] = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
+	if (IS_ERR(hd->pins[PIN_CTRL_E])) {
+		ret = PTR_ERR(hd->pins[PIN_CTRL_E]);
+		goto fail;
+	}
+
+	hd->pins[PIN_CTRL_RS] = devm_gpiod_get(dev, "rs", GPIOD_OUT_HIGH);
+	if (IS_ERR(hd->pins[PIN_CTRL_RS])) {
+		ret = PTR_ERR(hd->pins[PIN_CTRL_RS]);
+		goto fail;
+	}
+
+	/* Optional pins */
+	hd->pins[PIN_CTRL_RW] = devm_gpiod_get_optional(dev, "rw",
+							GPIOD_OUT_LOW);
+	if (IS_ERR(hd->pins[PIN_CTRL_RW])) {
+		ret = PTR_ERR(hd->pins[PIN_CTRL_RW]);
+		goto fail;
+	}
+
+	hd->pins[PIN_CTRL_BL] = devm_gpiod_get_optional(dev, "backlight",
+							GPIOD_OUT_LOW);
+	if (IS_ERR(hd->pins[PIN_CTRL_BL])) {
+		ret = PTR_ERR(hd->pins[PIN_CTRL_BL]);
+		goto fail;
+	}
+
+	/* Required properties */
+	ret = device_property_read_u32(dev, "display-height", &lcd->height);
+	if (ret)
+		goto fail;
+	ret = device_property_read_u32(dev, "display-width", &lcd->width);
+	if (ret)
+		goto fail;
+
+	/*
+	 * On displays with more than two rows, the internal buffer width is
+	 * usually equal to the display width
+	 */
+	if (lcd->height > 2)
+		lcd->bwidth = lcd->width;
+
+	/* Optional properties */
+	device_property_read_u32(dev, "internal-buffer-width", &lcd->bwidth);
+
+	lcd->ifwidth = ifwidth;
+	lcd->ops = ifwidth == 8 ? &hd44780_ops_gpio8 : &hd44780_ops_gpio4;
+
+	ret = charlcd_register(lcd);
+	if (ret)
+		goto fail;
+
+	platform_set_drvdata(pdev, lcd);
+	return 0;
+
+fail:
+	kfree(lcd);
+	return ret;
+}
+
+static int hd44780_remove(struct platform_device *pdev)
+{
+	struct charlcd *lcd = platform_get_drvdata(pdev);
+
+	charlcd_unregister(lcd);
+	return 0;
+}
+
+static const struct of_device_id hd44780_of_match[] = {
+	{ .compatible = "hit,hd44780" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, hd44780_of_match);
+
+static struct platform_driver hd44780_driver = {
+	.probe = hd44780_probe,
+	.remove = hd44780_remove,
+	.driver		= {
+		.name	= "hd44780",
+		.of_match_table = hd44780_of_match,
+	},
+};
+
+module_platform_driver(hd44780_driver);
+MODULE_DESCRIPTION("HD44780 Character LCD driver");
+MODULE_AUTHOR("Geert Uytterhoeven <geert@linux-m68k.org>");
+MODULE_LICENSE("GPL");