drivers: auxdisplay: hd44780: implement busy-flag polling mechanism

HD44780 controller can indicate via busy flag whether it's finished
processing current command. This allows for faster completion of HD44780
commands as seen from MCU perspective, as the MCU doesn't have to wait
for fixed long period of time. Implement this functionality.

Signed-off-by: Jan Kuliga <[email protected]>

Author: kuliga

drivers/auxdisplay/auxdisplay_hd44780.c

@@ -89,17 +89,76 @@ static void hd44780_pulse_enable_line(const struct device *dev)
 	k_sleep(K_NSEC(config->enable_line_fall_delay));
 }
 
-static void auxdisplay_hd44780_command(const struct device *dev, bool rs, uint8_t cmd,
-				       uint8_t mode)
+static inline void hd44780_set_rs_rw_lines(const struct device *dev, bool rs, bool rw)
+{
+	const struct auxdisplay_hd44780_config *const config = dev->config;
+
+	gpio_pin_set_dt(&config->rs_gpio, rs);
+	if (config->rw_gpio.port) {
+		gpio_pin_set_dt(&config->rw_gpio, rw);
+	}
+
+	k_sleep(K_NSEC(config->rs_line_delay));
+}
+
+static int hd44780_db_gpios_configure(const struct device *dev, uint8_t lsb_line,
+				      gpio_flags_t flags)
 {
+	const struct auxdisplay_hd44780_config *config = dev->config;
+	int rc;
+
+	for (int line = 7; line >= lsb_line; --line) {
+		rc = gpio_pin_configure_dt(&config->db_gpios[line], flags);
+		if (rc < 0) {
+			return rc;
+		}
+	}
+
+	return 0;
+}
+
+static void auxdisplay_hd44780_command(const struct device *dev, bool rs,
+				       uint8_t cmd, uint8_t mode)
+{
+	int rc;
 	const struct auxdisplay_hd44780_config *config = dev->config;
 	int8_t i = 7;
 	const int8_t lsb_line = (mode == AUXDISPLAY_HD44780_MODE_8_BIT) ? 0 : 4;
 	int8_t ncommands = (mode == AUXDISPLAY_HD44780_MODE_4_BIT) ? 2 : 1;
+	const bool check_busy_flag = (!config->rw_gpio.port ||
+				      (mode == AUXDISPLAY_HD44780_MODE_4_BIT_ONCE)) ?
+				      false : true;
 
-	gpio_pin_set_dt(&config->rs_gpio, rs);
-	k_sleep(K_NSEC(config->rs_line_delay));
+	if (check_busy_flag) {
+		bool busy;
+
+		rc = hd44780_db_gpios_configure(dev, lsb_line, GPIO_INPUT | GPIO_PULL_DOWN);
+		if (rc < 0) {
+			LOG_ERR("Configuration of db-gpios as inputs failed: %d", rc);
+			return;
+		}
+
+		hd44780_set_rs_rw_lines(dev, 0, 1);
+		do {
+			hd44780_pulse_enable_line(dev);
 
+			/* We don't care about the other pins. */
+			busy = gpio_pin_get_dt(&config->db_gpios[7]);
+
+			if (config->capabilities.mode == AUXDISPLAY_HD44780_MODE_4_BIT) {
+				/* In this mode we have to initiate two separate readbacks. */
+				hd44780_pulse_enable_line(dev);
+			}
+		} while (busy);
+
+		rc = hd44780_db_gpios_configure(dev, lsb_line, GPIO_OUTPUT);
+		if (rc < 0) {
+			LOG_ERR("Configuration of db-gpios as outputs failed: %d", rc);
+			return;
+		}
+	}
+
+	hd44780_set_rs_rw_lines(dev, rs, 0);
 	while (ncommands--) {
 		for (int8_t line = 7; line >= lsb_line; --line) {
 			gpio_pin_set_dt(&config->db_gpios[line], ((cmd & BIT(i)) ? 1 : 0));
@@ -108,6 +167,13 @@ static void auxdisplay_hd44780_command(const struct device *dev, bool rs, uint8_
 
 		hd44780_pulse_enable_line(dev);
 	}
+
+	if (!check_busy_flag) {
+		/* Sleep for a max execution time for a given instruction. */
+		uint16_t cmd_delay_us = (cmd == AUXDISPLAY_HD44780_CMD_CLEAR) ? 1520 : 37;
+
+		k_sleep(K_USEC(cmd_delay_us));
+	}
 }
 
 static void hd44780_ic_initialize(const struct device *dev)
@@ -172,17 +238,6 @@ static int auxdisplay_hd44780_init(const struct device *dev)
 		return rc;
 	}
 
-	if (config->rw_gpio.port) {
-		rc = gpio_pin_configure_dt(&config->rw_gpio, GPIO_OUTPUT);
-
-		if (rc < 0) {
-			LOG_ERR("Configuration of RW GPIO failed: %d", rc);
-			return rc;
-		}
-
-		gpio_pin_set_dt(&config->rw_gpio, 0);
-	}
-
 	rc = gpio_pin_configure_dt(&config->e_gpio, GPIO_OUTPUT);
 
 	if (rc < 0) {
@@ -215,6 +270,15 @@ static int auxdisplay_hd44780_init(const struct device *dev)
 		++i;
 	}
 
+	if (config->rw_gpio.port) {
+		rc = gpio_pin_configure_dt(&config->rw_gpio, GPIO_OUTPUT);
+
+		if (rc < 0) {
+			LOG_ERR("Configuration of RW GPIO failed: %d", rc);
+			return rc;
+		}
+	}
+
 	if (config->backlight_gpio.port) {
 		rc = gpio_pin_configure_dt(&config->backlight_gpio, GPIO_OUTPUT);