u-boot的LCD初始化代码是在common/lcd.c中，我们找到lcd_init函数：
该函数功能流程为：lcd_ctrl_init初始化了LCD的硬件参数---->开辟LCD的帧缓冲(缓冲基地址保存在了gd->fs_base变量中)—>清屏—>使能LCD—>设置LCD控制台参数
lcd_ctrl_init和lcd_enable函数是u-boot抽离出的函数接口，需要根据LCD的实际情况进行底层硬件的初始化操作实现这两个函数；除此之外还需要定义一个名为panel_info的vidinfo_t结构类型变量，该结构变量保存了LCD屏幕的大小和颜色位深，用于LCD屏幕的控制台显示。
我的屏幕是W43，分辨率480x272，驱动编写参考的TQ2440官方的LCD屏幕驱动代码修改而来。
添加LCD的相关配置宏：
gedit include/configs/tq2440.h
末尾添加如下代码：
/*
* LCD configuration
*/
#define CONFIG_LCD /* 该宏用于添加进LCD相关的编译项 */
#define LCD_BPP LCD_COLOR16 /* 每像素为16bits */
#define CONFIG_LCD_LOGO /* 显示LOGO */
#define CONFIG_LCD_INFO /* 显示用户自定义信息 */
#define CONFIG_LCD_INFO_BELOW_LOGO /* 用户自定义信息与LOGO的位置无关 */
#define CONFIG_SYS_WHITE_ON_BLACK /* 黑底白字 */
#define CONFIG_SYS_CONSOLE_IS_IN_ENV /* 控制台接收自环境变量 */
#define CONFIG_CONSOLE_MUX /* 定义该宏可支持将打印信息同时输出到串口和LCD */
#define CONFIG_CONSOLE_SCROLL_LINES 16 /* 屏幕显示总行数 */
/* 以下三个宏为我自己定义的 */
#define CONFIG_TQ2440_LCD /* 该宏用于将tq2440_lcd.c文件编译进来 */
#define LCD_XSIZE_TFT 480 /* LCD行数 */
#define LCD_YSIZE_TFT 272 /* LCD列数 */
#define MVAL 13
#define MVAL_USED 0 /* 0:each frame 1:rate by MVAL */
#define INVVDEN 1 /* 0:normal 1:inverted */
#define BSWP 0 /* byte swap control */
#define HWSWP 1 /* half word swap control */
#define CONFIG_TQ2440_LCD_VBPD 1
#define CONFIG_TQ2440_LCD_VFPD 1
#define CONFIG_TQ2440_LCD_VSPW 9
#define CONFIG_TQ2440_LCD_HBPD 1
#define CONFIG_TQ2440_LCD_HFPD 1
#define CONFIG_TQ2440_LCD_HSPW 40
#define CONFIG_TQ2440_LCD_CLKVAL 4
添加tq2440的LCD文件：
gedit drivers/video/tq2440_lcd.c
粘贴进如下代码：
#include <common.h>
#include <lcd.h>
#include <asm/system.h>
#include <asm/gpio.h>
#include <asm/arch/s3c24x0_cpu.h>
#include <lcd.h>
#include <version.h>
DECLARE_GLOBAL_DATA_PTR; /* 导入gd_t结构变量gd */
/* to get lower 21bits */
#define M5D(n) ((n) & 0x1FFFFF)
vidinfo_t panel_info =
{
.vl_col = LCD_XSIZE_TFT, /* 列数 */
.vl_row = LCD_YSIZE_TFT, /* 行数 */
.vl_bpix = LCD_BPP, /* 像素位数为16bits，该宏在tq2440.h中被定义 */
};
/* 将LCD缓冲数组转为二维数组来用 */
#define tq2440_lcd_frame_pbuf ((volatile unsigned short (*)[LCD_XSIZE_TFT])(gd->fb_base))
void tq2440_lcd_clear_screen(unsigned short color)
{
int x = 0, y = 0;
for (y = 0; y < LCD_YSIZE_TFT; y++)
{
for (x = 0; x < LCD_XSIZE_TFT; x++)
{
tq2440_lcd_frame_pbuf[y][x] = color;
}
}
}
void lcd_ctrl_init(void* lcdbase)
{
char vbpd = 0;
char vfpd = 0;
char vspw = 0;
char hbpd = 0;
char hfpd = 0;
char hspw = 0;
char clkval = 0;
char* lcdenv = NULL;
struct s3c24x0_gpio* const gpio = s3c24x0_get_base_gpio();
struct s3c24x0_lcd* const lcd = s3c24x0_get_base_lcd();
/* set lcd frame buffer start adddress */
lcd->lcdsaddr1 = (((unsigned int)tq2440_lcd_frame_pbuf >> 22) << 21) | M5D((unsigned int)tq2440_lcd_frame_pbuf >> 1);
/* set lcd frame buffer end adddress */
lcd->lcdsaddr2 = M5D(((unsigned int)tq2440_lcd_frame_pbuf + (LCD_XSIZE_TFT * LCD_YSIZE_TFT * 2)) >> 1);
/* set virtul screen page wigth */
lcd->lcdsaddr3 = (((LCD_XSIZE_TFT - LCD_XSIZE_TFT) / 1) << 11) | (LCD_XSIZE_TFT / 1);
lcdenv = getenv("dwVBPD");
vbpd = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_VBPD;
lcdenv = getenv("dwVFPD");
vfpd = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_VFPD;
lcdenv = getenv("dwVSPW");
vspw = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_VSPW;
lcdenv = getenv("dwHBPD");
hbpd = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_HBPD;
lcdenv = getenv("dwHFPD");
hfpd = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_HFPD;
lcdenv = getenv("dwHSPW");
hspw = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_HSPW;
lcdenv = getenv("dwCLKVAL");
clkval = lcdenv ? (int)simple_strtol(lcdenv, NULL, 10) : CONFIG_TQ2440_LCD_CLKVAL;
/* clear screen */
tq2440_lcd_clear_screen(0x0000);
/* initialize VD[7:0] */
gpio->gpcup = 0xFFFFFFFF;
gpio->gpccon = 0xAAAAAAAA;
/* initialize VD[15:8] */
gpio->gpdup = 0xFFFFFFFF;
gpio->gpdcon = 0xAAAAAAAA;
/* lcd config */
lcd->lcdcon1 = (clkval << 8) | (MVAL_USED << 7) | (3 << 5) | (12 << 1) | 0;
lcd->lcdcon2 = (vbpd << 24) | ((LCD_YSIZE_TFT - 1) << 14) | (vfpd << 6) | vspw;
lcd->lcdcon3 = (hbpd << 19) | ((LCD_XSIZE_TFT - 1) << 8) | hfpd;
lcd->lcdcon4 = (MVAL << 8) | hspw;
lcd->lcdcon5 = (1 << 11) | (0 << 10) | (1 << 9) | (1 << 8) | (0 << 7) | (0 << 6) | (1 << 3) | (BSWP << 1) | HWSWP;
/* make lcd sub interrupt */
lcd->lcdintmsk |= 0x3;
/* disable lpc3480 */
lcd->lpcsel &= ~(0x7);
/* disbale temp palette */
lcd->tpal = 0x0;
/* disable gpg4 pull-up */
gpio->gpgup &= ~(1 << 4);
/* set gpg4 mode to lcd_pwrdn */
gpio->gpgcon |= 3 << 8;
/* set gpg4 to high */
gpio->gpgdat |= 1 << 4;
/* enable pwren signal */
lcd->lcdcon5 |= 1 << 3;
/* set signal polarity to normal */
lcd->lcdcon5 &= ~(1 << 5);
}
void lcd_enable(void)
{
struct s3c24x0_lcd* const lcd = s3c24x0_get_base_lcd();
/* Enable the video output and the LCD control signal. */
lcd->lcdcon1 |= (1 << 0);
}
#ifdef CONFIG_LCD_INFO
void lcd_show_board_info(void)
{
lcd_printf("%s (%s - %s)\n", U_BOOT_VERSION, U_BOOT_DATE, U_BOOT_TIME);
}
#endif
添加进编译项：
gedit drivers/video/Makefile
末尾添加一行：
obj-$(CONFIG_TQ2440_LCD) += tq2440_lcd.o
编译后使用tftp下载到内存0x30008000处并运行程序，查看效果：
下面操作将输出信息重定向到LCD上显示：
使用以下命令查看可以将输出信息重定向到哪些设备：
coninfo
可以看到可以将输出信息重定向到串口和LCD，serial就是我们使用的串口一，标志为IO，也就是说可以输入输出，LCD为.O，也就是说只能输出不能输入。
将输出信息同时重定向到LCD和串口一：
setenv stdout 'lcd,serial'
ends…