drivers: mipi_dbi: add support for parallel 8080/6800 modes using GPIO

Introduce GPIO-based driver for MIPI DBI class that allows MIPI DBI
type A and B displays to be used on general platforms.

Since each data pin GPIO can be selected individually, the bus pins are
set in a loop, which has a significant negative impact on performance.
When using 8-bit mode and all the data GPIO pins are on the same port,
a look-up table is generated to set the whole port at once as a
performance optimization. This creates a ROM overhead of about 1 kiB.

Tested 8-bit 8080 mode with ILI9486 display on nRF52840-DK board.

Signed-off-by: Stefan Gloor <code@stefan-gloor.ch>

drivers/mipi_dbi/CMakeLists.txt

@@ -3,6 +3,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 zephyr_sources_ifdef(CONFIG_MIPI_DBI_SPI mipi_dbi_spi.c)
+zephyr_sources_ifdef(CONFIG_MIPI_DBI_BITBANG mipi_dbi_bitbang.c)
 zephyr_sources_ifdef(CONFIG_MIPI_DBI_SMARTBOND mipi_dbi_smartbond.c)
 zephyr_sources_ifdef(CONFIG_MIPI_DBI_NXP_LCDIC mipi_dbi_nxp_lcdic.c)
 zephyr_sources_ifdef(CONFIG_MIPI_DBI_NXP_FLEXIO_LCDIF mipi_dbi_nxp_flexio_lcdif.c)

drivers/mipi_dbi/Kconfig

@@ -22,6 +22,7 @@ config MIPI_DBI_INIT_PRIORITY
 	  MIPI-DBI Host Controllers initialization priority.
 
 source "drivers/mipi_dbi/Kconfig.spi"
+source "drivers/mipi_dbi/Kconfig.bitbang"
 source "drivers/mipi_dbi/Kconfig.smartbond"
 source "drivers/mipi_dbi/Kconfig.nxp_lcdic"
 source "drivers/mipi_dbi/Kconfig.nxp_flexio_lcdif"

drivers/mipi_dbi/Kconfig.bitbang

@@ -0,0 +1,11 @@
+# Copyright 2024 Stefan Gloor
+# SPDX-License-Identifier: Apache-2.0
+
+config MIPI_DBI_BITBANG
+	bool "MIPI DBI bit banging driver"
+	default y
+	depends on DT_HAS_ZEPHYR_MIPI_DBI_BITBANG_ENABLED
+	select GPIO
+	help
+	  Enable support for MIPI DBI bit banging driver. This driver implements
+	  a MIPI-DBI mode A and B compatible controller using GPIO.

drivers/mipi_dbi/mipi_dbi_bitbang.c

@@ -0,0 +1,347 @@
+/*
+ * MIPI DBI Type A and B driver using GPIO
+ *
+ * Copyright 2024 Stefan Gloor
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT zephyr_mipi_dbi_bitbang
+
+#include <zephyr/drivers/mipi_dbi.h>
+#include <zephyr/drivers/gpio.h>
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(mipi_dbi_bitbang, CONFIG_MIPI_DBI_LOG_LEVEL);
+
+/* The MIPI DBI spec allows 8, 9, and 16 bits */
+#define MIPI_DBI_MAX_DATA_BUS_WIDTH 16
+
+/* Compile in a data bus LUT for improved performance if at least one instance uses an 8-bit bus */
+#define _8_BIT_MODE_PRESENT(n) (DT_INST_PROP_LEN(n, data_gpios) == 8) |
+#define MIPI_DBI_8_BIT_MODE    DT_INST_FOREACH_STATUS_OKAY(_8_BIT_MODE_PRESENT) 0
+
+struct mipi_dbi_bitbang_config {
+	/* Parallel 8080/6800 data GPIOs */
+	const struct gpio_dt_spec data[MIPI_DBI_MAX_DATA_BUS_WIDTH];
+	const uint8_t data_bus_width;
+
+	/* Read (type B) GPIO */
+	const struct gpio_dt_spec rd;
+
+	/* Write (type B) or Read/!Write (type A) GPIO */
+	const struct gpio_dt_spec wr;
+
+	/* Enable/strobe GPIO (type A) */
+	const struct gpio_dt_spec e;
+
+	/* Chip-select GPIO */
+	const struct gpio_dt_spec cs;
+
+	/* Command/Data GPIO */
+	const struct gpio_dt_spec cmd_data;
+
+	/* Reset GPIO */
+	const struct gpio_dt_spec reset;
+
+#if MIPI_DBI_8_BIT_MODE
+	/* Data GPIO remap look-up table. Valid if mipi_dbi_bitbang_data.single_port is set */
+	const uint32_t data_lut[256];
+
+	/* Mask of all data pins. Valid if mipi_dbi_bitbang_data.single_port is set */
+	const uint32_t data_mask;
+#endif
+};
+
+struct mipi_dbi_bitbang_data {
+	struct k_mutex lock;
+
+#if MIPI_DBI_8_BIT_MODE
+	/* Indicates whether all data GPIO pins are on the same port and the data LUT is used. */
+	bool single_port;
+
+	/* Data GPIO port device. Valid if mipi_dbi_bitbang_data.single_port is set */
+	const struct device *data_port;
+#endif
+};
+
+static inline void mipi_dbi_bitbang_set_data_gpios(const struct mipi_dbi_bitbang_config *config,
+						   struct mipi_dbi_bitbang_data *data,
+						   uint32_t value)
+{
+#if MIPI_DBI_8_BIT_MODE
+	if (data->single_port) {
+		gpio_port_set_masked(data->data_port, config->data_mask, config->data_lut[value]);
+	} else {
+#endif
+		for (int i = 0; i < config->data_bus_width; i++) {
+			gpio_pin_set_dt(&config->data[i], (value & (1 << i)) != 0);
+		}
+#if MIPI_DBI_8_BIT_MODE
+	}
+#endif
+}
+
+static int mipi_dbi_bitbang_write_helper(const struct device *dev,
+					 const struct mipi_dbi_config *dbi_config, bool cmd_present,
+					 uint8_t cmd, const uint8_t *data_buf, size_t len)
+{
+	const struct mipi_dbi_bitbang_config *config = dev->config;
+	struct mipi_dbi_bitbang_data *data = dev->data;
+	int ret = 0;
+	uint8_t value;
+
+	ret = k_mutex_lock(&data->lock, K_FOREVER);
+	if (ret < 0) {
+		return ret;
+	}
+
+	switch (dbi_config->mode) {
+	case MIPI_DBI_MODE_8080_BUS_8_BIT:
+	case MIPI_DBI_MODE_8080_BUS_9_BIT:
+	case MIPI_DBI_MODE_8080_BUS_16_BIT:
+		gpio_pin_set_dt(&config->cs, 1);
+		if (cmd_present) {
+			gpio_pin_set_dt(&config->wr, 0);
+			gpio_pin_set_dt(&config->cmd_data, 0);
+			mipi_dbi_bitbang_set_data_gpios(config, data, cmd);
+			gpio_pin_set_dt(&config->wr, 1);
+		}
+		if (len > 0) {
+			gpio_pin_set_dt(&config->cmd_data, 1);
+			while (len > 0) {
+				value = *(data_buf++);
+				gpio_pin_set_dt(&config->wr, 0);
+				mipi_dbi_bitbang_set_data_gpios(config, data, value);
+				gpio_pin_set_dt(&config->wr, 1);
+				len--;
+			}
+		}
+		gpio_pin_set_dt(&config->cs, 0);
+		break;
+
+	/* Clocked E mode */
+	case MIPI_DBI_MODE_6800_BUS_8_BIT:
+	case MIPI_DBI_MODE_6800_BUS_9_BIT:
+	case MIPI_DBI_MODE_6800_BUS_16_BIT:
+		gpio_pin_set_dt(&config->cs, 1);
+		gpio_pin_set_dt(&config->wr, 0);
+		if (cmd_present) {
+			gpio_pin_set_dt(&config->e, 1);
+			gpio_pin_set_dt(&config->cmd_data, 0);
+			mipi_dbi_bitbang_set_data_gpios(config, data, cmd);
+			gpio_pin_set_dt(&config->e, 0);
+		}
+		if (len > 0) {
+			gpio_pin_set_dt(&config->cmd_data, 1);
+			while (len > 0) {
+				value = *(data_buf++);
+				gpio_pin_set_dt(&config->e, 1);
+				mipi_dbi_bitbang_set_data_gpios(config, data, value);
+				gpio_pin_set_dt(&config->e, 0);
+				len--;
+			}
+		}
+		gpio_pin_set_dt(&config->cs, 0);
+		break;
+
+	default:
+		LOG_ERR("MIPI DBI mode %u is not supported.", dbi_config->mode);
+		ret = -ENOTSUP;
+	}
+
+	k_mutex_unlock(&data->lock);
+	return ret;
+}
+
+static int mipi_dbi_bitbang_command_write(const struct device *dev,
+					  const struct mipi_dbi_config *dbi_config, uint8_t cmd,
+					  const uint8_t *data_buf, size_t len)
+{
+	return mipi_dbi_bitbang_write_helper(dev, dbi_config, true, cmd, data_buf, len);
+}
+
+static int mipi_dbi_bitbang_write_display(const struct device *dev,
+					  const struct mipi_dbi_config *dbi_config,
+					  const uint8_t *framebuf,
+					  struct display_buffer_descriptor *desc,
+					  enum display_pixel_format pixfmt)
+{
+	ARG_UNUSED(pixfmt);
+
+	return mipi_dbi_bitbang_write_helper(dev, dbi_config, false, 0x0, framebuf, desc->buf_size);
+}
+
+static int mipi_dbi_bitbang_reset(const struct device *dev, k_timeout_t delay)
+{
+	const struct mipi_dbi_bitbang_config *config = dev->config;
+	int ret;
+
+	LOG_DBG("Performing hw reset.");
+
+	ret = gpio_pin_set_dt(&config->reset, 1);
+	if (ret < 0) {
+		return ret;
+	}
+	k_sleep(delay);
+	return gpio_pin_set_dt(&config->reset, 0);
+}
+
+static int mipi_dbi_bitbang_init(const struct device *dev)
+{
+	const struct mipi_dbi_bitbang_config *config = dev->config;
+	const char *failed_pin = NULL;
+	int ret = 0;
+#if MIPI_DBI_8_BIT_MODE
+	struct mipi_dbi_bitbang_data *data = dev->data;
+#endif
+
+	if (gpio_is_ready_dt(&config->cmd_data)) {
+		ret = gpio_pin_configure_dt(&config->cmd_data, GPIO_OUTPUT_ACTIVE);
+		if (ret < 0) {
+			failed_pin = "cmd_data";
+			goto fail;
+		}
+		gpio_pin_set_dt(&config->cmd_data, 0);
+	}
+	if (gpio_is_ready_dt(&config->rd)) {
+		gpio_pin_configure_dt(&config->rd, GPIO_OUTPUT_ACTIVE);
+		/* Don't emit an error because this pin is unused in type A */
+		gpio_pin_set_dt(&config->rd, 1);
+	}
+	if (gpio_is_ready_dt(&config->wr)) {
+		ret = gpio_pin_configure_dt(&config->wr, GPIO_OUTPUT_ACTIVE);
+		if (ret < 0) {
+			failed_pin = "wr";
+			goto fail;
+		}
+		gpio_pin_set_dt(&config->wr, 1);
+	}
+	if (gpio_is_ready_dt(&config->e)) {
+		gpio_pin_configure_dt(&config->e, GPIO_OUTPUT_ACTIVE);
+		/* Don't emit an error because this pin is unused in type B */
+		gpio_pin_set_dt(&config->e, 0);
+	}
+	if (gpio_is_ready_dt(&config->cs)) {
+		ret = gpio_pin_configure_dt(&config->cs, GPIO_OUTPUT_ACTIVE);
+		if (ret < 0) {
+			failed_pin = "cs";
+			goto fail;
+		}
+		gpio_pin_set_dt(&config->cs, 0);
+	}
+	if (gpio_is_ready_dt(&config->reset)) {
+		ret = gpio_pin_configure_dt(&config->reset, GPIO_OUTPUT_ACTIVE);
+		if (ret < 0) {
+			failed_pin = "reset";
+			goto fail;
+		}
+		gpio_pin_set_dt(&config->reset, 0);
+	}
+	for (int i = 0; i < config->data_bus_width; i++) {
+		if (gpio_is_ready_dt(&config->data[i])) {
+			ret = gpio_pin_configure_dt(&config->data[i], GPIO_OUTPUT_ACTIVE);
+			if (ret < 0) {
+				failed_pin = "data";
+				goto fail;
+			}
+			gpio_pin_set_dt(&config->data[i], 0);
+		}
+	}
+
+#if MIPI_DBI_8_BIT_MODE
+	/* To optimize performance, we test whether all the data pins are
+	 * on the same port. If they are, we can set the whole port in one go
+	 * instead of setting each pin individually.
+	 * For 8-bit mode only because LUT size grows exponentially.
+	 */
+	if (config->data_bus_width == 8) {
+		data->single_port = true;
+		data->data_port = config->data[0].port;
+		for (int i = 1; i < config->data_bus_width; i++) {
+			if (data->data_port != config->data[i].port) {
+				data->single_port = false;
+			}
+		}
+	}
+	if (data->single_port) {
+		LOG_DBG("LUT optimization enabled. data_mask=0x%x", config->data_mask);
+	}
+#endif
+
+	return ret;
+fail:
+	LOG_ERR("Failed to configure %s GPIO pin.", failed_pin);
+	return ret;
+}
+
+static const struct mipi_dbi_driver_api mipi_dbi_bitbang_driver_api = {
+	.reset = mipi_dbi_bitbang_reset,
+	.command_write = mipi_dbi_bitbang_command_write,
+	.write_display = mipi_dbi_bitbang_write_display
+};
+
+/* This macro is repeatedly called by LISTIFY() at compile-time to generate the data bus LUT */
+#define LUT_GEN(i, n) (((i & (1 << 0)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 0)) : 0) |   \
+		       ((i & (1 << 1)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 1)) : 0) |   \
+		       ((i & (1 << 2)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 2)) : 0) |   \
+		       ((i & (1 << 3)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 3)) : 0) |   \
+		       ((i & (1 << 4)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 4)) : 0) |   \
+		       ((i & (1 << 5)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 5)) : 0) |   \
+		       ((i & (1 << 6)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 6)) : 0) |   \
+		       ((i & (1 << 7)) ? (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 7)) : 0))
+
+/* If at least one instance has an 8-bit bus, add a data look-up table to the read-only config.
+ * Whether or not it is valid and actually used for a particular instance is decided at runtime
+ * and stored in the instance's mipi_dbi_bitbang_data.single_port.
+ */
+#if MIPI_DBI_8_BIT_MODE
+#define DATA_LUT_OPTIMIZATION(n)                                                                   \
+		.data_lut = { LISTIFY(256, LUT_GEN, (,), n) },                                     \
+		.data_mask = ((1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 0)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 1)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 2)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 3)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 4)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 5)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 6)) |                   \
+			      (1 << DT_INST_GPIO_PIN_BY_IDX(n, data_gpios, 7)))
+#else
+#define DATA_LUT_OPTIMIZATION(n)
+#endif
+
+#define MIPI_DBI_BITBANG_INIT(n)                                                                   \
+	static const struct mipi_dbi_bitbang_config mipi_dbi_bitbang_config_##n = {                \
+		.data = {GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 0, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 1, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 2, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 3, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 4, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 5, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 6, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 7, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 8, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 9, {0}),                   \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 10, {0}),                  \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 11, {0}),                  \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 12, {0}),                  \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 13, {0}),                  \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 14, {0}),                  \
+			 GPIO_DT_SPEC_INST_GET_BY_IDX_OR(n, data_gpios, 15, {0})},                 \
+		.data_bus_width = DT_INST_PROP_LEN(n, data_gpios),                                 \
+		.rd = GPIO_DT_SPEC_INST_GET_OR(n, rd_gpios, {}),                                   \
+		.wr = GPIO_DT_SPEC_INST_GET_OR(n, wr_gpios, {}),                                   \
+		.e = GPIO_DT_SPEC_INST_GET_OR(n, e_gpios, {}),                                     \
+		.cs = GPIO_DT_SPEC_INST_GET_OR(n, cs_gpios, {}),                                   \
+		.cmd_data = GPIO_DT_SPEC_INST_GET_OR(n, dc_gpios, {}),                             \
+		.reset = GPIO_DT_SPEC_INST_GET_OR(n, reset_gpios, {}),                             \
+		DATA_LUT_OPTIMIZATION(n)                                                           \
+	};                                                                                         \
+	BUILD_ASSERT(DT_INST_PROP_LEN(n, data_gpios) < MIPI_DBI_MAX_DATA_BUS_WIDTH,                \
+		     "Number of data GPIOs in DT exceeds MIPI_DBI_MAX_DATA_BUS_WIDTH");            \
+	static struct mipi_dbi_bitbang_data mipi_dbi_bitbang_data_##n;                             \
+	DEVICE_DT_INST_DEFINE(n, mipi_dbi_bitbang_init, NULL, &mipi_dbi_bitbang_data_##n,          \
+			      &mipi_dbi_bitbang_config_##n, POST_KERNEL,                           \
+			      CONFIG_MIPI_DBI_INIT_PRIORITY, &mipi_dbi_bitbang_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(MIPI_DBI_BITBANG_INIT)