drivers/video/ssd2828.c - github/trini/u-boot - Gitiles

 /*
  * (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, reference_freq_khz, 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;
 		}
 	}

 	/*
 	 * Pick the reference clock for PLL. If we know the exact 'tx_clk'
 	 * clock speed, then everything is good. If not, then we can fallback
 	 * to 'pclk' (pixel clock from the parallel LCD interface). In the
 	 * case of using this fallback, it is necessary to have parallel LCD
 	 * already initialized and running at this point.
 	 */
 	reference_freq_khz = cfg->ssd2828_tx_clk_khz;
 	if (reference_freq_khz  == 0) {
 		reference_freq_khz = mode->pixclock_khz;
 		/* Use 'pclk' as the reference clock for PLL */
 		cfgr_reg |= SSD2828_CFGR_CSS;
 	}

 	/*
 	 * 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,
 				reference_freq_khz);
 	write_hw_register(cfg, SSD2828_PLCR, pll_config);

 	pll_freq_kbps = decode_pll_config(pll_config, reference_freq_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;
 }
	/*
	* (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, reference_freq_khz, 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;
	}
	}

	/*
	* Pick the reference clock for PLL. If we know the exact 'tx_clk'
	* clock speed, then everything is good. If not, then we can fallback
	* to 'pclk' (pixel clock from the parallel LCD interface). In the
	* case of using this fallback, it is necessary to have parallel LCD
	* already initialized and running at this point.
	*/
	reference_freq_khz = cfg->ssd2828_tx_clk_khz;
	if (reference_freq_khz == 0) {
	reference_freq_khz = mode->pixclock_khz;
	/* Use 'pclk' as the reference clock for PLL */
	cfgr_reg \|= SSD2828_CFGR_CSS;
	}

	/*
	* 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,
	reference_freq_khz);
	write_hw_register(cfg, SSD2828_PLCR, pll_config);

	pll_freq_kbps = decode_pll_config(pll_config, reference_freq_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;
	}