Add HD44780 character display connected via I2C I/O expander.
Re-uses the high-level interface of the existing HD44780 driver.
Signed-off-by: Ralf Schlatterbeck <r...@runtux.com>
---
drivers/auxdisplay/Kconfig | 14 +-
drivers/auxdisplay/Makefile | 1 +
drivers/auxdisplay/hd44780-pcf8574.c | 207 +++++++++++++++++++++++++++
3 files changed, 221 insertions(+), 1 deletion(-)
create mode 100644 drivers/auxdisplay/hd44780-pcf8574.c
diff --git a/drivers/auxdisplay/Kconfig b/drivers/auxdisplay/Kconfig
index 81757eeded68..1e373783c90e 100644
--- a/drivers/auxdisplay/Kconfig
+++ b/drivers/auxdisplay/Kconfig
@@ -17,7 +17,7 @@ menuconfig AUXDISPLAY
if AUXDISPLAY
config HD44780
- tristate "HD44780 Character LCD support"
+ tristate "HD44780 Character LCD support, parallel connection"
depends on GPIOLIB || COMPILE_TEST
select CHARLCD
help
@@ -27,6 +27,18 @@ config HD44780
kernel and started at boot.
If you don't understand what all this is about, say N.
+config HD44780_PCF8574
+ tristate "HD44780 Character LCD support, I2C-connection"
+ depends on I2C
+ select CHARLCD
+ help
+ Enable support for Character LCDs using a HD44780 controller.
+ The HD44780 is connected to an I2C bus via PCF8574 I/O expancer.
+ 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
diff --git a/drivers/auxdisplay/Makefile b/drivers/auxdisplay/Makefile
index cf54b5efb07e..cf008ce28545 100644
--- a/drivers/auxdisplay/Makefile
+++ b/drivers/auxdisplay/Makefile
@@ -9,5 +9,6 @@ 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-$(CONFIG_HD44780_PCF8574) += hd44780-pcf8574.o
obj-$(CONFIG_HT16K33) += ht16k33.o
obj-$(CONFIG_PARPORT_PANEL) += panel.o
diff --git a/drivers/auxdisplay/hd44780-pcf8574.c
b/drivers/auxdisplay/hd44780-pcf8574.c
new file mode 100644
index 000000000000..ffd9d604928b
--- /dev/null
+++ b/drivers/auxdisplay/hd44780-pcf8574.c
@@ -0,0 +1,207 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * HD44780 Character LCD driver for Linux
+ * With PCF8574 I2C I/O Expander
+ *
+ * Copyright (C) 2020, Ralf Schlatterbeck <r...@runtux.com>
+ */
+
+#define DEBUG
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/i2c.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+/*
+ * The display uses 4-bit mode (the I/O expander has only 8 bits)
+ * The control signals RS, R/W, E are on three bits and on many displays
+ * the backlight is on bit 3. The upper 4 bits are data.
+ */
+#define HD44780_RS_SHIFT 0
+#define HD44780_RW_SHIFT 1
+#define HD44780_E_SHIFT 2
+#define HD44780_BACKLIGHT_SHIFT 3
+
+#include "charlcd.h"
+
+struct hd44780 {
+ const struct i2c_client *i2c_client;
+ int backlight;
+};
+
+static void hd44780_backlight(struct charlcd *lcd, int on)
+{
+ struct hd44780 *hd = lcd->drvdata;
+ u8 b = BIT(HD44780_RW_SHIFT); /* Read-bit */
+
+ hd->backlight = on;
+ /* Note: We do not toggle the E-bit, display will ignore this */
+ b |= hd->backlight ? BIT(HD44780_BACKLIGHT_SHIFT) : 0;
+ (void)i2c_master_send(hd->i2c_client, &b, 1);
+}
+
+static int hd44780_send_nibble(struct hd44780 *hd, u8 outbyte)
+{
+ const struct i2c_client *i2c_client = hd->i2c_client;
+ u8 backlight = hd->backlight ? BIT(HD44780_BACKLIGHT_SHIFT) : 0;
+ u8 b = outbyte;
+ int err;
+ /*
+ * Transfers first send the output byte with the E-bit 0
+ * Then the spec says to wait for 20us, then we set the E-bit to 1
+ * and wait for 40us, then reset the E-bit again.
+ * A max-speed (400kbit/s) I2C transfer for a single byte will
+ * already take 25us. So the first delay of 20us can be skipped.
+ * The second delay becomes 40us - 25us = 15us.
+ */
+ b = (outbyte & ~BIT(HD44780_E_SHIFT)) | backlight;
+ dev_dbg(&i2c_client->dev, "I2C send: 0x%x", b);
+ err = i2c_master_send(i2c_client, &b, 1);
+ if (err < 0)
+ goto errout;
+ b = (outbyte | BIT(HD44780_E_SHIFT)) | backlight;
+ dev_dbg(&i2c_client->dev, "I2C send: 0x%x", b);
+ err = i2c_master_send(i2c_client, &b, 1);
+ if (err < 0)
+ goto errout;
+ udelay(15);
+ b = (outbyte & ~BIT(HD44780_E_SHIFT)) | backlight;
+ dev_dbg(&i2c_client->dev, "I2C send: 0x%x", b);
+ err = i2c_master_send(i2c_client, &b, 1);
+ if (err < 0)
+ goto errout;
+ return 0;
+errout:
+ dev_err(&i2c_client->dev, "Error sending to display: %d", err);
+ return err;
+}
+
+static void hd44780_write_cmd_raw_nibble(struct charlcd *lcd, int cmd)
+{
+ struct hd44780 *hd = lcd->drvdata;
+
+ (void)hd44780_send_nibble(hd, (cmd & 0x0F) << 4);
+ udelay(20);
+}
+
+/* Send a command to the LCD panel */
+static void hd44780_write_cmd(struct charlcd *lcd, int cmd)
+{
+ struct hd44780 *hd = lcd->drvdata;
+ int ret;
+
+ ret = hd44780_send_nibble(hd, (cmd & 0xF0));
+ if (ret)
+ return;
+ ret = hd44780_send_nibble(hd, (cmd << 4));
+ if (ret)
+ return;
+ /* The shortest command takes at least 120 us */
+ udelay(120);
+}
+
+/* Send data to the LCD panel */
+static void hd44780_write_data(struct charlcd *lcd, int data)
+{
+ struct hd44780 *hd = lcd->drvdata;
+ int ret;
+
+ ret = hd44780_send_nibble(hd, (data & 0xF0) | BIT(HD44780_RS_SHIFT));
+ if (ret)
+ return;
+ ret = hd44780_send_nibble(hd, (data << 4) | BIT(HD44780_RS_SHIFT));
+ if (ret)
+ return;
+ /* The shortest data takes at least 45 us */
+ udelay(45);
+}
+
+static const struct charlcd_ops hd44780_ops = {
+ .write_cmd = hd44780_write_cmd,
+ .write_cmd_raw4 = hd44780_write_cmd_raw_nibble,
+ .write_data = hd44780_write_data,
+ .backlight = hd44780_backlight,
+};
+
+static int hd44780_i2c_probe(struct i2c_client *client,
+ const struct i2c_device_id *id)
+{
+ struct device *dev = &client->dev;
+ struct charlcd *lcd;
+ struct hd44780 *hd;
+
+ int ret;
+
+ lcd = charlcd_alloc(sizeof(*hd));
+ if (!lcd)
+ return -ENOMEM;
+
+ hd = lcd->drvdata;
+ hd->i2c_client = client;
+ hd->backlight = 1;
+
+ /* Required properties */
+ ret = device_property_read_u32(dev, "display-height-chars",
+ &lcd->height);
+ if (ret)
+ goto fail;
+ ret = device_property_read_u32(dev, "display-width-chars", &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 = 4;
+ lcd->ops = &hd44780_ops;
+
+ ret = charlcd_register(lcd);
+ if (ret)
+ goto fail;
+ dev_info(&client->dev, "Found HD44780 display");
+
+ return 0;
+
+fail:
+ charlcd_free(lcd);
+ return ret;
+}
+
+static int hd44780_i2c_remove(struct i2c_client *client)
+{
+ struct charlcd *lcd = i2c_get_clientdata(client);
+
+ charlcd_unregister(lcd);
+
+ charlcd_free(lcd);
+ return 0;
+}
+
+static const struct of_device_id hd44780_of_match[] = {
+ { .compatible = "hit,hd44780+nxp,pcf8575" },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, hd44780_of_match);
+
+static struct i2c_driver hd44780_i2c_driver = {
+ .driver = {
+ .name = "hd44780+pcf8574",
+ .of_match_table = hd44780_of_match,
+ },
+ .probe = hd44780_i2c_probe,
+ .remove = hd44780_i2c_remove,
+};
+module_i2c_driver(hd44780_i2c_driver);
+
+MODULE_DESCRIPTION("HD44780 + PCF8574 I2C Character LCD driver");
+MODULE_AUTHOR("Ralf Schlatterbeck <r...@runtux.com>");
+MODULE_LICENSE("GPL");
--
2.20.1
