video: Add support for SSD2828 (parallel LCD to MIPI bridge)

SSD2828 can take pixel data coming from a parallel LCD interface
and translate it on the fly into MIPI DSI interface for driving
a MIPI compatible TFT display. SSD2828 is configured over SPI
interface, which may or may not have MISO pin wired up on some
hardware. So a write-only SPI mode also has to be supported.

The SSD2828 support code is implemented as a utility function
and needs to be called from real display drivers, which are
responsible for driving parallel LCD hardware in front of the
video pipeline. The usage instructions are provided as comments
in the header file.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

4 files changed, 616 insertions, 0 deletions

diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index fdbf3f64f2..ec14a371dc 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -6,3 +6,73 @@ config VIDEO_X86
 	  Turn on this option to enable a very simple driver which uses vesa
 	  to discover the video mode and then provides a frame buffer for use
 	  by U-Boot.
+
+config VIDEO_LCD_SSD2828
+	bool "SSD2828 bridge chip"
+	default n
+	---help---
+	Support for the SSD2828 bridge chip, which can take pixel data coming
+	from a parallel LCD interface and translate it on the fly into MIPI DSI
+	interface for driving a MIPI compatible LCD panel. It uses SPI for
+	configuration.
+
+config VIDEO_LCD_SSD2828_TX_CLK
+	int "SSD2828 TX_CLK frequency (in MHz)"
+	depends on VIDEO_LCD_SSD2828
+	---help---
+	The frequency of the crystal, which is clocking SSD2828. It may be
+	anything in the 8MHz-30MHz range and the exact value should be
+	retrieved from the board schematics. Or in the case of Allwinner
+	hardware, it can be usually found as 'lcd_xtal_freq' variable in
+	FEX files.
+
+config VIDEO_LCD_SSD2828_RESET
+	string "RESET pin of SSD2828"
+	depends on VIDEO_LCD_SSD2828
+	default ""
+	---help---
+	The reset pin of SSD2828 chip. This takes a string in the format
+	understood by 'name_to_gpio' function, e.g. PH1 for pin 1 of port H.
+
+config VIDEO_LCD_SPI_CS
+	string "SPI CS pin for LCD related config job"
+	depends on VIDEO_LCD_SSD2828
+	default ""
+	---help---
+	This is one of the SPI communication pins, involved in setting up a
+	working LCD configuration. The exact role of SPI may differ for
+	different hardware setups. The option takes a string in the format
+	understood by 'name_to_gpio' function, e.g. PH1 for pin 1 of port H.
+
+config VIDEO_LCD_SPI_SCLK
+	string "SPI SCLK pin for LCD related config job"
+	depends on VIDEO_LCD_SSD2828
+	default ""
+	---help---
+	This is one of the SPI communication pins, involved in setting up a
+	working LCD configuration. The exact role of SPI may differ for
+	different hardware setups. The option takes a string in the format
+	understood by 'name_to_gpio' function, e.g. PH1 for pin 1 of port H.
+
+config VIDEO_LCD_SPI_MOSI
+	string "SPI MOSI pin for LCD related config job"
+	depends on VIDEO_LCD_SSD2828
+	default ""
+	---help---
+	This is one of the SPI communication pins, involved in setting up a
+	working LCD configuration. The exact role of SPI may differ for
+	different hardware setups. The option takes a string in the format
+	understood by 'name_to_gpio' function, e.g. PH1 for pin 1 of port H.
+
+config VIDEO_LCD_SPI_MISO
+	string "SPI MISO pin for LCD related config job (optional)"
+	depends on VIDEO_LCD_SSD2828
+	default ""
+	---help---
+	This is one of the SPI communication pins, involved in setting up a
+	working LCD configuration. The exact role of SPI may differ for
+	different hardware setups. If wired up, this pin may provide additional
+	useful functionality. Such as bi-directional communication with the
+	hardware and LCD panel id retrieval (if the panel can report it). The
+	option takes a string in the format understood by 'name_to_gpio'
+	function, e.g. PH1 for pin 1 of port H.
diff --git a/drivers/video/Makefile b/drivers/video/Makefile
index 42b1eaaf76..36298684bf 100644
--- a/drivers/video/Makefile
+++ b/drivers/video/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_VIDEO_COREBOOT) += coreboot_fb.o
 obj-$(CONFIG_VIDEO_CT69000) += ct69000.o videomodes.o
 obj-$(CONFIG_VIDEO_DA8XX) += da8xx-fb.o videomodes.o
 obj-$(CONFIG_VIDEO_IMX25LCDC) += imx25lcdc.o videomodes.o
+obj-$(CONFIG_VIDEO_LCD_SSD2828) += ssd2828.o
 obj-$(CONFIG_VIDEO_MB862xx) += mb862xx.o videomodes.o
 obj-$(CONFIG_VIDEO_MB86R0xGDC) += mb86r0xgdc.o videomodes.o
 obj-$(CONFIG_VIDEO_MX3) += mx3fb.o videomodes.o
diff --git a/drivers/video/ssd2828.c b/drivers/video/ssd2828.c
new file mode 100644
index 0000000000..be68d38f81
--- /dev/null
+++ b/drivers/video/ssd2828.c
@@ -0,0 +1,422 @@
+/*
+ * (C) 2015 Siarhei Siamashka <siarhei.siamashka@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * Support for the SSD2828 bridge chip, which can take pixel data coming
+ * from a parallel LCD interface and translate it on the flight into MIPI DSI
+ * interface for driving a MIPI compatible TFT display.
+ */
+
+#include <common.h>
+#include <mipi_display.h>
+#include <asm/arch/gpio.h>
+#include <asm/gpio.h>
+
+#include "videomodes.h"
+#include "ssd2828.h"
+
+#define		SSD2828_DIR	0xB0
+#define		SSD2828_VICR1	0xB1
+#define		SSD2828_VICR2	0xB2
+#define		SSD2828_VICR3	0xB3
+#define		SSD2828_VICR4	0xB4
+#define		SSD2828_VICR5	0xB5
+#define		SSD2828_VICR6	0xB6
+#define		SSD2828_CFGR	0xB7
+#define		SSD2828_VCR	0xB8
+#define		SSD2828_PCR	0xB9
+#define		SSD2828_PLCR	0xBA
+#define		SSD2828_CCR	0xBB
+#define		SSD2828_PSCR1	0xBC
+#define		SSD2828_PSCR2	0xBD
+#define		SSD2828_PSCR3	0xBE
+#define		SSD2828_PDR	0xBF
+#define		SSD2828_OCR	0xC0
+#define		SSD2828_MRSR	0xC1
+#define		SSD2828_RDCR	0xC2
+#define		SSD2828_ARSR	0xC3
+#define		SSD2828_LCR	0xC4
+#define		SSD2828_ICR	0xC5
+#define		SSD2828_ISR	0xC6
+#define		SSD2828_ESR	0xC7
+#define		SSD2828_DAR1	0xC9
+#define		SSD2828_DAR2	0xCA
+#define		SSD2828_DAR3	0xCB
+#define		SSD2828_DAR4	0xCC
+#define		SSD2828_DAR5	0xCD
+#define		SSD2828_DAR6	0xCE
+#define		SSD2828_HTTR1	0xCF
+#define		SSD2828_HTTR2	0xD0
+#define		SSD2828_LRTR1	0xD1
+#define		SSD2828_LRTR2	0xD2
+#define		SSD2828_TSR	0xD3
+#define		SSD2828_LRR	0xD4
+#define		SSD2828_PLLR	0xD5
+#define		SSD2828_TR	0xD6
+#define		SSD2828_TECR	0xD7
+#define		SSD2828_ACR1	0xD8
+#define		SSD2828_ACR2	0xD9
+#define		SSD2828_ACR3	0xDA
+#define		SSD2828_ACR4	0xDB
+#define		SSD2828_IOCR	0xDC
+#define		SSD2828_VICR7	0xDD
+#define		SSD2828_LCFR	0xDE
+#define		SSD2828_DAR7	0xDF
+#define		SSD2828_PUCR1	0xE0
+#define		SSD2828_PUCR2	0xE1
+#define		SSD2828_PUCR3	0xE2
+#define		SSD2828_CBCR1	0xE9
+#define		SSD2828_CBCR2	0xEA
+#define		SSD2828_CBSR	0xEB
+#define		SSD2828_ECR	0xEC
+#define		SSD2828_VSDR	0xED
+#define		SSD2828_TMR	0xEE
+#define		SSD2828_GPIO1	0xEF
+#define		SSD2828_GPIO2	0xF0
+#define		SSD2828_DLYA01	0xF1
+#define		SSD2828_DLYA23	0xF2
+#define		SSD2828_DLYB01	0xF3
+#define		SSD2828_DLYB23	0xF4
+#define		SSD2828_DLYC01	0xF5
+#define		SSD2828_DLYC23	0xF6
+#define		SSD2828_ACR5	0xF7
+#define		SSD2828_RR	0xFF
+
+#define	SSD2828_CFGR_HS					(1 << 0)
+#define	SSD2828_CFGR_CKE				(1 << 1)
+#define	SSD2828_CFGR_SLP				(1 << 2)
+#define	SSD2828_CFGR_VEN				(1 << 3)
+#define	SSD2828_CFGR_HCLK				(1 << 4)
+#define	SSD2828_CFGR_CSS				(1 << 5)
+#define	SSD2828_CFGR_DCS				(1 << 6)
+#define	SSD2828_CFGR_REN				(1 << 7)
+#define	SSD2828_CFGR_ECD				(1 << 8)
+#define	SSD2828_CFGR_EOT				(1 << 9)
+#define	SSD2828_CFGR_LPE				(1 << 10)
+#define	SSD2828_CFGR_TXD				(1 << 11)
+
+#define	SSD2828_VIDEO_MODE_NON_BURST_WITH_SYNC_PULSES	(0 << 2)
+#define	SSD2828_VIDEO_MODE_NON_BURST_WITH_SYNC_EVENTS	(1 << 2)
+#define	SSD2828_VIDEO_MODE_BURST			(2 << 2)
+
+#define	SSD2828_VIDEO_PIXEL_FORMAT_16BPP		0
+#define	SSD2828_VIDEO_PIXEL_FORMAT_18BPP_PACKED		1
+#define	SSD2828_VIDEO_PIXEL_FORMAT_18BPP_LOOSELY_PACKED	2
+#define	SSD2828_VIDEO_PIXEL_FORMAT_24BPP		3
+
+#define	SSD2828_LP_CLOCK_DIVIDER(n)			(((n) - 1) & 0x3F)
+
+/*
+ * SPI transfer, using the "24-bit 3 wire" mode (that's how it is called in
+ * the SSD2828 documentation). The 'dout' input parameter specifies 24-bits
+ * of data to be written to SSD2828. Returns the lowest 16-bits of data,
+ * that is received back.
+ */
+static u32 soft_spi_xfer_24bit_3wire(const struct ssd2828_config *drv, u32 dout)
+{
+	int j, bitlen = 24;
+	u32 tmpdin = 0;
+	/*
+	 * According to the "24 Bit 3 Wire SPI Interface Timing Characteristics"
+	 * and "TX_CLK Timing Characteristics" tables in the SSD2828 datasheet,
+	 * the lowest possible 'tx_clk' clock frequency is 8MHz, and SPI runs
+	 * at 1/8 of that after reset. So using 1 microsecond delays is safe in
+	 * the main loop. But the delays around chip select pin manipulations
+	 * need to be longer (up to 16 'tx_clk' cycles, or 2 microseconds in
+	 * the worst case).
+	 */
+	const int spi_delay_us = 1;
+	const int spi_cs_delay_us = 2;
+
+	gpio_set_value(drv->csx_pin, 0);
+	udelay(spi_cs_delay_us);
+	for (j = bitlen - 1; j >= 0; j--) {
+		gpio_set_value(drv->sck_pin, 0);
+		gpio_set_value(drv->sdi_pin, (dout & (1 << j)) != 0);
+		udelay(spi_delay_us);
+		if (drv->sdo_pin != -1)
+			tmpdin = (tmpdin << 1) | gpio_get_value(drv->sdo_pin);
+		gpio_set_value(drv->sck_pin, 1);
+		udelay(spi_delay_us);
+	}
+	udelay(spi_cs_delay_us);
+	gpio_set_value(drv->csx_pin, 1);
+	udelay(spi_cs_delay_us);
+	return tmpdin & 0xFFFF;
+}
+
+/*
+ * Read from a SSD2828 hardware register (regnum >= 0xB0)
+ */
+static u32 read_hw_register(const struct ssd2828_config *cfg, u8 regnum)
+{
+	soft_spi_xfer_24bit_3wire(cfg, 0x700000 | regnum);
+	return soft_spi_xfer_24bit_3wire(cfg, 0x730000);
+}
+
+/*
+ * Write to a SSD2828 hardware register (regnum >= 0xB0)
+ */
+static void write_hw_register(const struct ssd2828_config *cfg, u8 regnum,
+			      u16 val)
+{
+	soft_spi_xfer_24bit_3wire(cfg, 0x700000 | regnum);
+	soft_spi_xfer_24bit_3wire(cfg, 0x720000 | val);
+}
+
+/*
+ * Send MIPI command to the LCD panel (cmdnum < 0xB0)
+ */
+static void send_mipi_dcs_command(const struct ssd2828_config *cfg, u8 cmdnum)
+{
+	/* Set packet size to 1 (a single command with no parameters) */
+	write_hw_register(cfg, SSD2828_PSCR1, 1);
+	/* Send the command */
+	write_hw_register(cfg, SSD2828_PDR, cmdnum);
+}
+
+/*
+ * Reset SSD2828
+ */
+static void ssd2828_reset(const struct ssd2828_config *cfg)
+{
+	/* RESET needs 10 milliseconds according to the datasheet */
+	gpio_set_value(cfg->reset_pin, 0);
+	mdelay(10);
+	gpio_set_value(cfg->reset_pin, 1);
+	mdelay(10);
+}
+
+static int ssd2828_enable_gpio(const struct ssd2828_config *cfg)
+{
+	if (gpio_request(cfg->csx_pin, "ssd2828_csx")) {
+		printf("SSD2828: request for 'ssd2828_csx' pin failed\n");
+		return 1;
+	}
+	if (gpio_request(cfg->sck_pin, "ssd2828_sck")) {
+		gpio_free(cfg->csx_pin);
+		printf("SSD2828: request for 'ssd2828_sck' pin failed\n");
+		return 1;
+	}
+	if (gpio_request(cfg->sdi_pin, "ssd2828_sdi")) {
+		gpio_free(cfg->csx_pin);
+		gpio_free(cfg->sck_pin);
+		printf("SSD2828: request for 'ssd2828_sdi' pin failed\n");
+		return 1;
+	}
+	if (gpio_request(cfg->reset_pin, "ssd2828_reset")) {
+		gpio_free(cfg->csx_pin);
+		gpio_free(cfg->sck_pin);
+		gpio_free(cfg->sdi_pin);
+		printf("SSD2828: request for 'ssd2828_reset' pin failed\n");
+		return 1;
+	}
+	if (cfg->sdo_pin != -1 && gpio_request(cfg->sdo_pin, "ssd2828_sdo")) {
+		gpio_free(cfg->csx_pin);
+		gpio_free(cfg->sck_pin);
+		gpio_free(cfg->sdi_pin);
+		gpio_free(cfg->reset_pin);
+		printf("SSD2828: request for 'ssd2828_sdo' pin failed\n");
+		return 1;
+	}
+	gpio_direction_output(cfg->reset_pin, 0);
+	gpio_direction_output(cfg->csx_pin, 1);
+	gpio_direction_output(cfg->sck_pin, 1);
+	gpio_direction_output(cfg->sdi_pin, 1);
+	if (cfg->sdo_pin != -1)
+		gpio_direction_input(cfg->sdo_pin);
+
+	return 0;
+}
+
+static int ssd2828_free_gpio(const struct ssd2828_config *cfg)
+{
+	gpio_free(cfg->csx_pin);
+	gpio_free(cfg->sck_pin);
+	gpio_free(cfg->sdi_pin);
+	gpio_free(cfg->reset_pin);
+	if (cfg->sdo_pin != -1)
+		gpio_free(cfg->sdo_pin);
+	return 1;
+}
+
+/*
+ * PLL configuration register settings.
+ *
+ * See the "PLL Configuration Register Description" in the SSD2828 datasheet.
+ */
+static u32 construct_pll_config(u32 desired_pll_freq_kbps,
+				u32 reference_freq_khz)
+{
+	u32 div_factor = 1, mul_factor, fr = 0;
+	u32 output_freq_kbps;
+
+	/* The intermediate clock after division can't be less than 5MHz */
+	while (reference_freq_khz / (div_factor + 1) >= 5000)
+		div_factor++;
+	if (div_factor > 31)
+		div_factor = 31;
+
+	mul_factor = DIV_ROUND_UP(desired_pll_freq_kbps * div_factor,
+				  reference_freq_khz);
+
+	output_freq_kbps = reference_freq_khz * mul_factor / div_factor;
+
+	if (output_freq_kbps >= 501000)
+		fr = 3;
+	else if (output_freq_kbps >= 251000)
+		fr = 2;
+	else if (output_freq_kbps >= 126000)
+		fr = 1;
+
+	return (fr << 14) | (div_factor << 8) | mul_factor;
+}
+
+static u32 decode_pll_config(u32 pll_config, u32 reference_freq_khz)
+{
+	u32 mul_factor = pll_config & 0xFF;
+	u32 div_factor = (pll_config >> 8) & 0x1F;
+	if (mul_factor == 0)
+		mul_factor = 1;
+	if (div_factor == 0)
+		div_factor = 1;
+	return reference_freq_khz * mul_factor / div_factor;
+}
+
+static int ssd2828_configure_video_interface(const struct ssd2828_config *cfg,
+					     const struct ctfb_res_modes *mode)
+{
+	u32 val;
+
+	/* RGB Interface Control Register 1 */
+	write_hw_register(cfg, SSD2828_VICR1, (mode->vsync_len << 8) |
+					      (mode->hsync_len));
+
+	/* RGB Interface Control Register 2 */
+	u32 vbp = mode->vsync_len + mode->upper_margin;
+	u32 hbp = mode->hsync_len + mode->left_margin;
+	write_hw_register(cfg, SSD2828_VICR2, (vbp << 8) | hbp);
+
+	/* RGB Interface Control Register 3 */
+	write_hw_register(cfg, SSD2828_VICR3, (mode->lower_margin << 8) |
+					      (mode->right_margin));
+
+	/* RGB Interface Control Register 4 */
+	write_hw_register(cfg, SSD2828_VICR4, mode->xres);
+
+	/* RGB Interface Control Register 5 */
+	write_hw_register(cfg, SSD2828_VICR5, mode->yres);
+
+	/* RGB Interface Control Register 6 */
+	val = SSD2828_VIDEO_MODE_BURST;
+	switch (cfg->ssd2828_color_depth) {
+	case 16:
+		val |= SSD2828_VIDEO_PIXEL_FORMAT_16BPP;
+		break;
+	case 18:
+		val |= cfg->mipi_dsi_loosely_packed_pixel_format ?
+			SSD2828_VIDEO_PIXEL_FORMAT_18BPP_LOOSELY_PACKED :
+			SSD2828_VIDEO_PIXEL_FORMAT_18BPP_PACKED;
+		break;
+	case 24:
+		val |= SSD2828_VIDEO_PIXEL_FORMAT_24BPP;
+		break;
+	default:
+		printf("SSD2828: unsupported color depth\n");
+		return 1;
+	}
+	write_hw_register(cfg, SSD2828_VICR6, val);
+
+	/* Lane Configuration Register */
+	write_hw_register(cfg, SSD2828_LCFR,
+			  cfg->mipi_dsi_number_of_data_lanes - 1);
+
+	return 0;
+}
+
+int ssd2828_init(const struct ssd2828_config *cfg,
+		 const struct ctfb_res_modes *mode)
+{
+	u32 lp_div, pll_freq_kbps, pll_config;
+	/* The LP clock speed is limited by 10MHz */
+	const u32 mipi_dsi_low_power_clk_khz = 10000;
+	/*
+	 * This is just the reset default value of CFGR register (0x301).
+	 * Because we are not always able to read back from SPI, have
+	 * it initialized here.
+	 */
+	u32 cfgr_reg = SSD2828_CFGR_EOT | /* EOT Packet Enable */
+		       SSD2828_CFGR_ECD | /* Disable ECC and CRC */
+		       SSD2828_CFGR_HS;   /* Data lanes are in HS mode */
+
+	/* Initialize the pins */
+	if (ssd2828_enable_gpio(cfg) != 0)
+		return 1;
+
+	/* Reset the chip */
+	ssd2828_reset(cfg);
+
+	/*
+	 * If there is a pin to read data back from SPI, then we are lucky. Try
+	 * to check if SPI is configured correctly and SSD2828 is actually able
+	 * to talk back.
+	 */
+	if (cfg->sdo_pin != -1) {
+		if (read_hw_register(cfg, SSD2828_DIR) != 0x2828 ||
+		    read_hw_register(cfg, SSD2828_CFGR) != cfgr_reg) {
+			printf("SSD2828: SPI communication failed.\n");
+			ssd2828_free_gpio(cfg);
+			return 1;
+		}
+	}
+
+	/*
+	 * Setup the parallel LCD timings in the appropriate registers.
+	 */
+	if (ssd2828_configure_video_interface(cfg, mode) != 0) {
+		ssd2828_free_gpio(cfg);
+		return 1;
+	}
+
+	/* Configuration Register */
+	cfgr_reg &= ~SSD2828_CFGR_HS;  /* Data lanes are in LP mode */
+	cfgr_reg |= SSD2828_CFGR_CKE;  /* Clock lane is in HS mode */
+	cfgr_reg |= SSD2828_CFGR_DCS;  /* Only use DCS packets */
+	write_hw_register(cfg, SSD2828_CFGR, cfgr_reg);
+
+	/* PLL Configuration Register */
+	pll_config = construct_pll_config(
+				cfg->mipi_dsi_bitrate_per_data_lane_mbps * 1000,
+				cfg->ssd2828_tx_clk_khz);
+	write_hw_register(cfg, SSD2828_PLCR, pll_config);
+
+	pll_freq_kbps = decode_pll_config(pll_config, cfg->ssd2828_tx_clk_khz);
+	lp_div = DIV_ROUND_UP(pll_freq_kbps, mipi_dsi_low_power_clk_khz * 8);
+
+	/* VC Control Register */
+	write_hw_register(cfg, SSD2828_VCR, 0);
+
+	/* Clock Control Register */
+	write_hw_register(cfg, SSD2828_CCR, SSD2828_LP_CLOCK_DIVIDER(lp_div));
+
+	/* PLL Control Register */
+	write_hw_register(cfg, SSD2828_PCR, 1); /* Enable PLL */
+
+	/* Wait for PLL lock */
+	udelay(500);
+
+	send_mipi_dcs_command(cfg, MIPI_DCS_EXIT_SLEEP_MODE);
+	mdelay(cfg->mipi_dsi_delay_after_exit_sleep_mode_ms);
+
+	send_mipi_dcs_command(cfg, MIPI_DCS_SET_DISPLAY_ON);
+	mdelay(cfg->mipi_dsi_delay_after_set_display_on_ms);
+
+	cfgr_reg |= SSD2828_CFGR_HS;    /* Enable HS mode for data lanes */
+	cfgr_reg |= SSD2828_CFGR_VEN;   /* Enable video pipeline */
+	write_hw_register(cfg, SSD2828_CFGR, cfgr_reg);
+
+	return 0;
+}
diff --git a/drivers/video/ssd2828.h b/drivers/video/ssd2828.h
new file mode 100644
index 0000000000..14b96c5143
--- /dev/null
+++ b/drivers/video/ssd2828.h
@@ -0,0 +1,123 @@
+/*
+ * (C) 2015 Siarhei Siamashka <siarhei.siamashka@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * Support for the SSD2828 bridge chip, which can take pixel data coming
+ * from a parallel LCD interface and translate it on the flight into MIPI DSI
+ * interface for driving a MIPI compatible TFT display.
+ *
+ * Implemented as a utility function. To be used from display drivers, which are
+ * responsible for driving parallel LCD hardware in front of the video pipeline.
+ */
+
+#ifndef _SSD2828_H
+#define _SSD2828_H
+
+struct ctfb_res_modes;
+
+struct ssd2828_config {
+	/*********************************************************************/
+	/* SSD2828 configuration                                             */
+	/*********************************************************************/
+
+	/*
+	 * The pins, which are used for SPI communication. This is only used
+	 * for configuring SSD2828, so the performance is irrelevant (only
+	 * around a hundred of bytes is moved). Also these can be any arbitrary
+	 * GPIO pins (not necessarily the pins having hardware SPI function).
+	 * Moreover, the 'sdo' pin may be even not wired up in some devices.
+	 *
+	 * These configuration variables need to be set as pin numbers for
+	 * the standard u-boot GPIO interface (gpio_get_value/gpio_set_value
+	 * functions). Note that -1 value can be used for the pins, which are
+	 * not really wired up.
+	 */
+	int csx_pin;
+	int sck_pin;
+	int sdi_pin;
+	int sdo_pin;
+	/* SSD2828 reset pin (shared with LCD panel reset) */
+	int reset_pin;
+
+	/*
+	 * The SSD2828 has its own dedicated clock source 'tx_clk' (connected
+	 * to TX_CLK_XIO/TX_CLK_XIN pins), which is necessary at least for
+	 * clocking SPI after reset. The exact clock speed is not strictly,
+	 * defined, but the datasheet says that it must be somewhere in the
+	 * 8MHz - 30MHz range (see "TX_CLK Timing" section). It is used as
+	 * a reference clock for PLL and must be set correctly.
+	 */
+	int ssd2828_tx_clk_khz;
+
+	/*
+	 * This is not a property of the used LCD panel, but more like a
+	 * property of the SSD2828 wiring. See the "SSD2828QN4 RGB data
+	 * arrangement" table in the datasheet. The SSD2828 pins are arranged
+	 * in such a way that 18bpp and 24bpp configurations are completely
+	 * incompatible with each other.
+	 *
+	 * Depending on the color depth, this must be set to 16, 18 or 24.
+	 */
+	int ssd2828_color_depth;
+
+	/*********************************************************************/
+	/* LCD panel configuration                                           */
+	/*********************************************************************/
+
+	/*
+	 * The number of lanes in the MIPI DSI interface. May vary from 1 to 4.
+	 *
+	 * This information can be found in the LCD panel datasheet.
+	 */
+	int mipi_dsi_number_of_data_lanes;
+
+	/*
+	 * Data transfer bit rate per lane. Please note that it is expected
+	 * to be higher than the pixel clock rate of the used video mode when
+	 * multiplied by the number of lanes. This is perfectly normal because
+	 * MIPI DSI handles data transfers in periodic bursts, and uses the
+	 * idle time between bursts for sending configuration information and
+	 * commands. Or just for saving power.
+	 *
+	 * The necessary Mbps/lane information can be found in the LCD panel
+	 * datasheet. Note that the transfer rate can't be always set precisely
+	 * and it may be rounded *up* (introducing no more than 10Mbps error).
+	 */
+	int mipi_dsi_bitrate_per_data_lane_mbps;
+
+	/*
+	 * Setting this to 1 enforces packing of 18bpp pixel data in 24bpp
+	 * envelope when sending it over the MIPI DSI link.
+	 *
+	 * If unsure, set to 0.
+	 */
+	int mipi_dsi_loosely_packed_pixel_format;
+
+	/*
+	 * According to the "Example for system sleep in and out" section in
+	 * the SSD2828 datasheet, some LCD panel specific delays are necessary
+	 * after MIPI DCS commands EXIT_SLEEP_MODE and SET_DISPLAY_ON.
+	 *
+	 * For example, Allwinner uses 100 milliseconds delay after
+	 * EXIT_SLEEP_MODE and 200 milliseconds delay after SET_DISPLAY_ON.
+	 */
+	int mipi_dsi_delay_after_exit_sleep_mode_ms;
+	int mipi_dsi_delay_after_set_display_on_ms;
+};
+
+/*
+ * Initialize the SSD2828 chip. It needs the 'ssd2828_config' structure
+ * and also the video mode timings.
+ *
+ * The right place to insert this function call is after the parallel LCD
+ * interface is initialized and before turning on the backlight. This is
+ * advised in the "Example for system sleep in and out" section of the
+ * SSD2828 datasheet.
+ */
+int ssd2828_init(const struct ssd2828_config *cfg,
+		 const struct ctfb_res_modes *mode);
+
+#endif