video: backlight: add ili922x lcd driver

Add LCD driver for Ilitek ILI9221/ILI9222 controller.  The driver uses
SPI interface for controller access and configuration and RGB interface
for graphics data transfer.

Signed-off-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 563 insertions, 0 deletions

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index a4481dfadfd5..2e166c3fc4c3 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -59,6 +59,13 @@ config LCD_LTV350QV
 
 	  The LTV350QV panel is present on all ATSTK1000 boards.
 
+config LCD_ILI922X
+	tristate "ILI Technology ILI9221/ILI9222 support"
+	depends on SPI
+	help
+	  If you have a panel based on the ILI9221/9222 controller
+	  chip then say y to include a driver for it.
+
 config LCD_ILI9320
 	tristate "ILI Technology ILI9320 controller support"
 	depends on SPI
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index 96c4d620c5ce..92711fe60464 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -5,6 +5,7 @@ obj-$(CONFIG_LCD_CLASS_DEVICE)		+= lcd.o
 obj-$(CONFIG_LCD_CORGI)			+= corgi_lcd.o
 obj-$(CONFIG_LCD_HP700)			+= jornada720_lcd.o
 obj-$(CONFIG_LCD_HX8357)		+= hx8357.o
+obj-$(CONFIG_LCD_ILI922X)		+= ili922x.o
 obj-$(CONFIG_LCD_ILI9320)		+= ili9320.o
 obj-$(CONFIG_LCD_L4F00242T03)		+= l4f00242t03.o
 obj-$(CONFIG_LCD_LD9040)		+= ld9040.o
diff --git a/drivers/video/backlight/ili922x.c b/drivers/video/backlight/ili922x.c
new file mode 100644
index 000000000000..8b8465ed0014
--- /dev/null
+++ b/drivers/video/backlight/ili922x.c
@@ -0,0 +1,555 @@
+/*
+ * (C) Copyright 2008
+ * Stefano Babic, DENX Software Engineering, sbabic@denx.de.
+ *
+ * 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.
+ *
+ * This driver implements a lcd device for the ILITEK 922x display
+ * controller. The interface to the display is SPI and the display's
+ * memory is cyclically updated over the RGB interface.
+ */
+
+#include <linux/fb.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/lcd.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+#include <linux/spi/spi.h>
+#include <linux/string.h>
+
+/* Register offset, see manual section 8.2 */
+#define REG_START_OSCILLATION			0x00
+#define REG_DRIVER_CODE_READ			0x00
+#define REG_DRIVER_OUTPUT_CONTROL		0x01
+#define REG_LCD_AC_DRIVEING_CONTROL		0x02
+#define REG_ENTRY_MODE				0x03
+#define REG_COMPARE_1				0x04
+#define REG_COMPARE_2				0x05
+#define REG_DISPLAY_CONTROL_1			0x07
+#define REG_DISPLAY_CONTROL_2			0x08
+#define REG_DISPLAY_CONTROL_3			0x09
+#define REG_FRAME_CYCLE_CONTROL			0x0B
+#define REG_EXT_INTF_CONTROL			0x0C
+#define REG_POWER_CONTROL_1			0x10
+#define REG_POWER_CONTROL_2			0x11
+#define REG_POWER_CONTROL_3			0x12
+#define REG_POWER_CONTROL_4			0x13
+#define REG_RAM_ADDRESS_SET			0x21
+#define REG_WRITE_DATA_TO_GRAM			0x22
+#define REG_RAM_WRITE_MASK1			0x23
+#define REG_RAM_WRITE_MASK2			0x24
+#define REG_GAMMA_CONTROL_1			0x30
+#define REG_GAMMA_CONTROL_2			0x31
+#define REG_GAMMA_CONTROL_3			0x32
+#define REG_GAMMA_CONTROL_4			0x33
+#define REG_GAMMA_CONTROL_5			0x34
+#define REG_GAMMA_CONTROL_6			0x35
+#define REG_GAMMA_CONTROL_7			0x36
+#define REG_GAMMA_CONTROL_8			0x37
+#define REG_GAMMA_CONTROL_9			0x38
+#define REG_GAMMA_CONTROL_10			0x39
+#define REG_GATE_SCAN_CONTROL			0x40
+#define REG_VERT_SCROLL_CONTROL			0x41
+#define REG_FIRST_SCREEN_DRIVE_POS		0x42
+#define REG_SECOND_SCREEN_DRIVE_POS		0x43
+#define REG_RAM_ADDR_POS_H			0x44
+#define REG_RAM_ADDR_POS_V			0x45
+#define REG_OSCILLATOR_CONTROL			0x4F
+#define REG_GPIO				0x60
+#define REG_OTP_VCM_PROGRAMMING			0x61
+#define REG_OTP_VCM_STATUS_ENABLE		0x62
+#define REG_OTP_PROGRAMMING_ID_KEY		0x65
+
+/*
+ * maximum frequency for register access
+ * (not for the GRAM access)
+ */
+#define ILITEK_MAX_FREQ_REG	4000000
+
+/*
+ * Device ID as found in the datasheet (supports 9221 and 9222)
+ */
+#define ILITEK_DEVICE_ID	0x9220
+#define ILITEK_DEVICE_ID_MASK	0xFFF0
+
+/* Last two bits in the START BYTE */
+#define START_RS_INDEX		0
+#define START_RS_REG		1
+#define START_RW_WRITE		0
+#define START_RW_READ		1
+
+/**
+ * START_BYTE(id, rs, rw)
+ *
+ * Set the start byte according to the required operation.
+ * The start byte is defined as:
+ *   ----------------------------------
+ *  | 0 | 1 | 1 | 1 | 0 | ID | RS | RW |
+ *   ----------------------------------
+ * @id: display's id as set by the manufacturer
+ * @rs: operation type bit, one of:
+ *	  - START_RS_INDEX	set the index register
+ *	  - START_RS_REG	write/read registers/GRAM
+ * @rw: read/write operation
+ *	 - START_RW_WRITE	write
+ *	 - START_RW_READ	read
+ */
+#define START_BYTE(id, rs, rw)	\
+	(0x70 | (((id) & 0x01) << 2) | (((rs) & 0x01) << 1) | ((rw) & 0x01))
+
+/**
+ * CHECK_FREQ_REG(spi_device s, spi_transfer x) - Check the frequency
+ *	for the SPI transfer. According to the datasheet, the controller
+ *	accept higher frequency for the GRAM transfer, but it requires
+ *	lower frequency when the registers are read/written.
+ *	The macro sets the frequency in the spi_transfer structure if
+ *	the frequency exceeds the maximum value.
+ */
+#define CHECK_FREQ_REG(s, x)	\
+	do {			\
+		if (s->max_speed_hz > ILITEK_MAX_FREQ_REG)	\
+			((struct spi_transfer *)x)->speed_hz =	\
+					ILITEK_MAX_FREQ_REG;	\
+	} while (0)
+
+#define CMD_BUFSIZE		16
+
+#define POWER_IS_ON(pwr)	((pwr) <= FB_BLANK_NORMAL)
+
+#define set_tx_byte(b)		(tx_invert ? ~(b) : b)
+
+/**
+ * ili922x_id - id as set by manufacturer
+ */
+static int ili922x_id = 1;
+module_param(ili922x_id, int, 0);
+
+static int tx_invert;
+module_param(tx_invert, int, 0);
+
+/**
+ * driver's private structure
+ */
+struct ili922x {
+	struct spi_device *spi;
+	struct lcd_device *ld;
+	int power;
+};
+
+/**
+ * ili922x_read_status - read status register from display
+ * @spi: spi device
+ * @rs:  output value
+ */
+static int ili922x_read_status(struct spi_device *spi, u16 *rs)
+{
+	struct spi_message msg;
+	struct spi_transfer xfer;
+	unsigned char tbuf[CMD_BUFSIZE];
+	unsigned char rbuf[CMD_BUFSIZE];
+	int ret, i;
+
+	memset(&xfer, 0, sizeof(struct spi_transfer));
+	spi_message_init(&msg);
+	xfer.tx_buf = tbuf;
+	xfer.rx_buf = rbuf;
+	xfer.cs_change = 1;
+	CHECK_FREQ_REG(spi, &xfer);
+
+	tbuf[0] = set_tx_byte(START_BYTE(ili922x_id, START_RS_INDEX,
+					 START_RW_READ));
+	/*
+	 * we need 4-byte xfer here due to invalid dummy byte
+	 * received after start byte
+	 */
+	for (i = 1; i < 4; i++)
+		tbuf[i] = set_tx_byte(0);	/* dummy */
+
+	xfer.bits_per_word = 8;
+	xfer.len = 4;
+	spi_message_add_tail(&xfer, &msg);
+	ret = spi_sync(spi, &msg);
+	if (ret < 0) {
+		dev_dbg(&spi->dev, "Error sending SPI message 0x%x", ret);
+		return ret;
+	}
+
+	*rs = (rbuf[2] << 8) + rbuf[3];
+	return 0;
+}
+
+/**
+ * ili922x_read - read register from display
+ * @spi: spi device
+ * @reg: offset of the register to be read
+ * @rx:  output value
+ */
+static int ili922x_read(struct spi_device *spi, u8 reg, u16 *rx)
+{
+	struct spi_message msg;
+	struct spi_transfer xfer_regindex, xfer_regvalue;
+	unsigned char tbuf[CMD_BUFSIZE];
+	unsigned char rbuf[CMD_BUFSIZE];
+	int ret, len = 0, send_bytes;
+
+	memset(&xfer_regindex, 0, sizeof(struct spi_transfer));
+	memset(&xfer_regvalue, 0, sizeof(struct spi_transfer));
+	spi_message_init(&msg);
+	xfer_regindex.tx_buf = tbuf;
+	xfer_regindex.rx_buf = rbuf;
+	xfer_regindex.cs_change = 1;
+	CHECK_FREQ_REG(spi, &xfer_regindex);
+
+	tbuf[0] = set_tx_byte(START_BYTE(ili922x_id, START_RS_INDEX,
+					 START_RW_WRITE));
+	tbuf[1] = set_tx_byte(0);
+	tbuf[2] = set_tx_byte(reg);
+	xfer_regindex.bits_per_word = 8;
+	len = xfer_regindex.len = 3;
+	spi_message_add_tail(&xfer_regindex, &msg);
+
+	send_bytes = len;
+
+	tbuf[len++] = set_tx_byte(START_BYTE(ili922x_id, START_RS_REG,
+					     START_RW_READ));
+	tbuf[len++] = set_tx_byte(0);
+	tbuf[len] = set_tx_byte(0);
+
+	xfer_regvalue.cs_change = 1;
+	xfer_regvalue.len = 3;
+	xfer_regvalue.tx_buf = &tbuf[send_bytes];
+	xfer_regvalue.rx_buf = &rbuf[send_bytes];
+	CHECK_FREQ_REG(spi, &xfer_regvalue);
+
+	spi_message_add_tail(&xfer_regvalue, &msg);
+	ret = spi_sync(spi, &msg);
+	if (ret < 0) {
+		dev_dbg(&spi->dev, "Error sending SPI message 0x%x", ret);
+		return ret;
+	}
+
+	*rx = (rbuf[1 + send_bytes] << 8) + rbuf[2 + send_bytes];
+	return 0;
+}
+
+/**
+ * ili922x_write - write a controller register
+ * @spi: struct spi_device *
+ * @reg: offset of the register to be written
+ * @value: value to be written
+ */
+static int ili922x_write(struct spi_device *spi, u8 reg, u16 value)
+{
+	struct spi_message msg;
+	struct spi_transfer xfer_regindex, xfer_regvalue;
+	unsigned char tbuf[CMD_BUFSIZE];
+	unsigned char rbuf[CMD_BUFSIZE];
+	int ret, len = 0;
+
+	memset(&xfer_regindex, 0, sizeof(struct spi_transfer));
+	memset(&xfer_regvalue, 0, sizeof(struct spi_transfer));
+
+	spi_message_init(&msg);
+	xfer_regindex.tx_buf = tbuf;
+	xfer_regindex.rx_buf = rbuf;
+	xfer_regindex.cs_change = 1;
+	CHECK_FREQ_REG(spi, &xfer_regindex);
+
+	tbuf[0] = set_tx_byte(START_BYTE(ili922x_id, START_RS_INDEX,
+					 START_RW_WRITE));
+	tbuf[1] = set_tx_byte(0);
+	tbuf[2] = set_tx_byte(reg);
+	xfer_regindex.bits_per_word = 8;
+	xfer_regindex.len = 3;
+	spi_message_add_tail(&xfer_regindex, &msg);
+
+	ret = spi_sync(spi, &msg);
+
+	spi_message_init(&msg);
+	len = 0;
+	tbuf[0] = set_tx_byte(START_BYTE(ili922x_id, START_RS_REG,
+					 START_RW_WRITE));
+	tbuf[1] = set_tx_byte((value & 0xFF00) >> 8);
+	tbuf[2] = set_tx_byte(value & 0x00FF);
+
+	xfer_regvalue.cs_change = 1;
+	xfer_regvalue.len = 3;
+	xfer_regvalue.tx_buf = tbuf;
+	xfer_regvalue.rx_buf = rbuf;
+	CHECK_FREQ_REG(spi, &xfer_regvalue);
+
+	spi_message_add_tail(&xfer_regvalue, &msg);
+
+	ret = spi_sync(spi, &msg);
+	if (ret < 0) {
+		dev_err(&spi->dev, "Error sending SPI message 0x%x", ret);
+		return ret;
+	}
+	return 0;
+}
+
+#ifdef DEBUG
+/**
+ * ili922x_reg_dump - dump all registers
+ */
+static void ili922x_reg_dump(struct spi_device *spi)
+{
+	u8 reg;
+	u16 rx;
+
+	dev_dbg(&spi->dev, "ILI922x configuration registers:\n");
+	for (reg = REG_START_OSCILLATION;
+	     reg <= REG_OTP_PROGRAMMING_ID_KEY; reg++) {
+		ili922x_read(spi, reg, &rx);
+		dev_dbg(&spi->dev, "reg @ 0x%02X: 0x%04X\n", reg, rx);
+	}
+}
+#else
+static inline void ili922x_reg_dump(struct spi_device *spi) {}
+#endif
+
+/**
+ * set_write_to_gram_reg - initialize the display to write the GRAM
+ * @spi: spi device
+ */
+static void set_write_to_gram_reg(struct spi_device *spi)
+{
+	struct spi_message msg;
+	struct spi_transfer xfer;
+	unsigned char tbuf[CMD_BUFSIZE];
+
+	memset(&xfer, 0, sizeof(struct spi_transfer));
+
+	spi_message_init(&msg);
+	xfer.tx_buf = tbuf;
+	xfer.rx_buf = NULL;
+	xfer.cs_change = 1;
+
+	tbuf[0] = START_BYTE(ili922x_id, START_RS_INDEX, START_RW_WRITE);
+	tbuf[1] = 0;
+	tbuf[2] = REG_WRITE_DATA_TO_GRAM;
+
+	xfer.bits_per_word = 8;
+	xfer.len = 3;
+	spi_message_add_tail(&xfer, &msg);
+	spi_sync(spi, &msg);
+}
+
+/**
+ * ili922x_poweron - turn the display on
+ * @spi: spi device
+ *
+ * The sequence to turn on the display is taken from
+ * the datasheet and/or the example code provided by the
+ * manufacturer.
+ */
+static int ili922x_poweron(struct spi_device *spi)
+{
+	int ret;
+
+	/* Power on */
+	ret = ili922x_write(spi, REG_POWER_CONTROL_1, 0x0000);
+	usleep_range(10000, 10500);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_2, 0x0000);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_3, 0x0000);
+	msleep(40);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_4, 0x0000);
+	msleep(40);
+	/* register 0x56 is not documented in the datasheet */
+	ret += ili922x_write(spi, 0x56, 0x080F);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_1, 0x4240);
+	usleep_range(10000, 10500);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_2, 0x0000);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_3, 0x0014);
+	msleep(40);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_4, 0x1319);
+	msleep(40);
+
+	return ret;
+}
+
+/**
+ * ili922x_poweroff - turn the display off
+ * @spi: spi device
+ */
+static int ili922x_poweroff(struct spi_device *spi)
+{
+	int ret;
+
+	/* Power off */
+	ret = ili922x_write(spi, REG_POWER_CONTROL_1, 0x0000);
+	usleep_range(10000, 10500);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_2, 0x0000);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_3, 0x0000);
+	msleep(40);
+	ret += ili922x_write(spi, REG_POWER_CONTROL_4, 0x0000);
+	msleep(40);
+
+	return ret;
+}
+
+/**
+ * ili922x_display_init - initialize the display by setting
+ *			  the configuration registers
+ * @spi: spi device
+ */
+static void ili922x_display_init(struct spi_device *spi)
+{
+	ili922x_write(spi, REG_START_OSCILLATION, 1);
+	usleep_range(10000, 10500);
+	ili922x_write(spi, REG_DRIVER_OUTPUT_CONTROL, 0x691B);
+	ili922x_write(spi, REG_LCD_AC_DRIVEING_CONTROL, 0x0700);
+	ili922x_write(spi, REG_ENTRY_MODE, 0x1030);
+	ili922x_write(spi, REG_COMPARE_1, 0x0000);
+	ili922x_write(spi, REG_COMPARE_2, 0x0000);
+	ili922x_write(spi, REG_DISPLAY_CONTROL_1, 0x0037);
+	ili922x_write(spi, REG_DISPLAY_CONTROL_2, 0x0202);
+	ili922x_write(spi, REG_DISPLAY_CONTROL_3, 0x0000);
+	ili922x_write(spi, REG_FRAME_CYCLE_CONTROL, 0x0000);
+
+	/* Set RGB interface */
+	ili922x_write(spi, REG_EXT_INTF_CONTROL, 0x0110);
+
+	ili922x_poweron(spi);
+
+	ili922x_write(spi, REG_GAMMA_CONTROL_1, 0x0302);
+	ili922x_write(spi, REG_GAMMA_CONTROL_2, 0x0407);
+	ili922x_write(spi, REG_GAMMA_CONTROL_3, 0x0304);
+	ili922x_write(spi, REG_GAMMA_CONTROL_4, 0x0203);
+	ili922x_write(spi, REG_GAMMA_CONTROL_5, 0x0706);
+	ili922x_write(spi, REG_GAMMA_CONTROL_6, 0x0407);
+	ili922x_write(spi, REG_GAMMA_CONTROL_7, 0x0706);
+	ili922x_write(spi, REG_GAMMA_CONTROL_8, 0x0000);
+	ili922x_write(spi, REG_GAMMA_CONTROL_9, 0x0C06);
+	ili922x_write(spi, REG_GAMMA_CONTROL_10, 0x0F00);
+	ili922x_write(spi, REG_RAM_ADDRESS_SET, 0x0000);
+	ili922x_write(spi, REG_GATE_SCAN_CONTROL, 0x0000);
+	ili922x_write(spi, REG_VERT_SCROLL_CONTROL, 0x0000);
+	ili922x_write(spi, REG_FIRST_SCREEN_DRIVE_POS, 0xDB00);
+	ili922x_write(spi, REG_SECOND_SCREEN_DRIVE_POS, 0xDB00);
+	ili922x_write(spi, REG_RAM_ADDR_POS_H, 0xAF00);
+	ili922x_write(spi, REG_RAM_ADDR_POS_V, 0xDB00);
+	ili922x_reg_dump(spi);
+	set_write_to_gram_reg(spi);
+}
+
+static int ili922x_lcd_power(struct ili922x *lcd, int power)
+{
+	int ret = 0;
+
+	if (POWER_IS_ON(power) && !POWER_IS_ON(lcd->power))
+		ret = ili922x_poweron(lcd->spi);
+	else if (!POWER_IS_ON(power) && POWER_IS_ON(lcd->power))
+		ret = ili922x_poweroff(lcd->spi);
+
+	if (!ret)
+		lcd->power = power;
+
+	return ret;
+}
+
+static int ili922x_set_power(struct lcd_device *ld, int power)
+{
+	struct ili922x *ili = lcd_get_data(ld);
+
+	return ili922x_lcd_power(ili, power);
+}
+
+static int ili922x_get_power(struct lcd_device *ld)
+{
+	struct ili922x *ili = lcd_get_data(ld);
+
+	return ili->power;
+}
+
+static struct lcd_ops ili922x_ops = {
+	.get_power = ili922x_get_power,
+	.set_power = ili922x_set_power,
+};
+
+static int ili922x_probe(struct spi_device *spi)
+{
+	struct ili922x *ili;
+	struct lcd_device *lcd;
+	int ret;
+	u16 reg = 0;
+
+	ili = devm_kzalloc(&spi->dev, sizeof(*ili), GFP_KERNEL);
+	if (!ili) {
+		dev_err(&spi->dev, "cannot alloc priv data\n");
+		return -ENOMEM;
+	}
+
+	ili->spi = spi;
+	dev_set_drvdata(&spi->dev, ili);
+
+	/* check if the device is connected */
+	ret = ili922x_read(spi, REG_DRIVER_CODE_READ, &reg);
+	if (ret || ((reg & ILITEK_DEVICE_ID_MASK) != ILITEK_DEVICE_ID)) {
+		dev_err(&spi->dev,
+			"no LCD found: Chip ID 0x%x, ret %d\n",
+			reg, ret);
+		return -ENODEV;
+	} else {
+		dev_info(&spi->dev, "ILI%x found, SPI freq %d, mode %d\n",
+			 reg, spi->max_speed_hz, spi->mode);
+	}
+
+	ret = ili922x_read_status(spi, &reg);
+	if (ret) {
+		dev_err(&spi->dev, "reading RS failed...\n");
+		return ret;
+	} else
+		dev_dbg(&spi->dev, "status: 0x%x\n", reg);
+
+	ili922x_display_init(spi);
+
+	ili->power = FB_BLANK_POWERDOWN;
+
+	lcd = lcd_device_register("ili922xlcd", &spi->dev, ili,
+				  &ili922x_ops);
+	if (IS_ERR(lcd)) {
+		dev_err(&spi->dev, "cannot register LCD\n");
+		return PTR_ERR(lcd);
+	}
+
+	ili->ld = lcd;
+	spi_set_drvdata(spi, ili);
+
+	ili922x_lcd_power(ili, FB_BLANK_UNBLANK);
+
+	return 0;
+}
+
+static int ili922x_remove(struct spi_device *spi)
+{
+	struct ili922x *ili = spi_get_drvdata(spi);
+
+	ili922x_poweroff(spi);
+	lcd_device_unregister(ili->ld);
+	return 0;
+}
+
+static struct spi_driver ili922x_driver = {
+	.driver = {
+		.name = "ili922x",
+		.owner = THIS_MODULE,
+	},
+	.probe = ili922x_probe,
+	.remove = ili922x_remove,
+};
+
+module_spi_driver(ili922x_driver);
+
+MODULE_AUTHOR("Stefano Babic <sbabic@denx.de>");
+MODULE_DESCRIPTION("ILI9221/9222 LCD driver");
+MODULE_LICENSE("GPL");
+MODULE_PARM_DESC(ili922x_id, "set controller identifier (default=1)");
+MODULE_PARM_DESC(tx_invert, "invert bytes before sending");