LCD能够支持彩色图像的显示和视频的播放，是一种很重要的输出设备，在一些嵌入式人机交互系统中，也往往需要lcd进行显示。Linux内核已经支持了s3c2416的lcd控制器。

1. lcd设备

lcd设备包含了名字、独有的资源等等一些驱动程序的硬件或自定义信息。 通过platform_add_devices(platform_device_register)函数将定义的平台设备注册到内核中，用于匹配设备驱动。

内核在drivers\video\fbdev\s3c-fb.c中实现了s3c2416 lcd驱动，lcd设备平台代码如下:

Eastar: /arch/arm/mach-s3c24xx/mach-home2416.c

static struct s3c_fb_pd_win home2416_fb_win[] = {
       [0]= {
              .default_bpp  = 16,
              .max_bpp      = 32,
              .xres           = 800,
              .yres           = 480,
       },
};
static struct fb_videomode home2416_lcd_timing = {
       .pixclock = 41094,
       .left_margin   = 19,
       .right_margin       = 37,
       .upper_margin     = 10,
       .lower_margin      = 26,
       .hsync_len     = 27,
       .vsync_len     = 13,
       .xres           = 800,
       .yres           = 480,
};
static void s3c2416_fb_gpio_setup_24bpp(void)
{
       unsignedint gpio;
       for(gpio = S3C2410_GPC(1); gpio <= S3C2410_GPC(4); gpio++) {
              s3c_gpio_cfgpin(gpio,S3C_GPIO_SFN(2));
              s3c_gpio_setpull(gpio,S3C_GPIO_PULL_NONE);
       }
       for(gpio = S3C2410_GPC(8); gpio <= S3C2410_GPC(15); gpio++) {
              s3c_gpio_cfgpin(gpio,S3C_GPIO_SFN(2));
              s3c_gpio_setpull(gpio,S3C_GPIO_PULL_NONE);
       }
       for(gpio = S3C2410_GPD(0); gpio <= S3C2410_GPD(15); gpio++) {
              s3c_gpio_cfgpin(gpio,S3C_GPIO_SFN(2));
              s3c_gpio_setpull(gpio,S3C_GPIO_PULL_NONE);
       }
}
static struct s3c_fb_platdata home2416_fb_platdata = {
       .win[0]          = &home2416_fb_win[0],
       .vtiming  = &home2416_lcd_timing,
       .setup_gpio   = s3c2416_fb_gpio_setup_24bpp,
       .vidcon0 = VIDCON0_VIDOUT_RGB | VIDCON0_PNRMODE_RGB,
       .vidcon1 = VIDCON1_INV_HSYNC | VIDCON1_INV_VSYNC,
};
static struct resource s3c_fb_resource[]= {
       [0]= DEFINE_RES_MEM(S3C_PA_FB, SZ_16K),
       [1]= DEFINE_RES_IRQ(IRQ_LCD_VSYNC),
       [2]= DEFINE_RES_IRQ(IRQ_LCD_FIFO),
       [3]= DEFINE_RES_IRQ(IRQ_LCD_SYSTEM),
};
struct platform_device s3c_device_fb = {
       .name            = "s3c-fb",
       .id          = -1,
       .num_resources    = ARRAY_SIZE(s3c_fb_resource),
       .resource       = s3c_fb_resource,
       .dev        = {
              .dma_mask          = &samsung_device_dma_mask,
              .coherent_dma_mask  = DMA_BIT_MASK(32),
       },
};
void __init s3c_fb_set_platdata(structs3c_fb_platdata *pd)
{
       s3c_set_platdata(pd,sizeof(struct s3c_fb_platdata),
                     &s3c_device_fb);
}

在板级初始化函数 home2416_machine_init() 中加入lcd平台数据 s3c_fb_set_platdata(&home2416_fb_platdata) ，在 static struct platform_device *home2416_devices[] 板级平台设备列表中加入 &s3c_device_fb ，使lcd设备能够注册到内核中。

内核在 drivers\video\backlight\pwm_bl.c 中实现了基于pwm方式的lcd背光驱动，背光设备平台代码如下：

Eastar: arch/arm/mach-s3c24**/mach-home2416.c

static int s3c2416_backlight_init(structdevice *dev)
{
       gpio_request(S3C2410_GPB(0),"Backlight");    //使用的IO口为: GPB.0
       gpio_direction_output(S3C2410_GPB(0),0);
       s3c_gpio_setpull(S3C2410_GPB(0),S3C_GPIO_PULL_NONE);
       s3c_gpio_cfgpin(S3C2410_GPB(0),S3C2410_GPB0_TOUT0);
       return 0;
}
static int s3c2416_backlight_notify(struct device *dev, int brightness)
{
    if(!brightness) 
    {
        gpio_direction_output(S3C2410_GPB(0),0);
    }
    else 
    {
        gpio_direction_output(S3C2410_GPB(0),0);
        s3c_gpio_setpull(S3C2410_GPB(0),S3C_GPIO_PULL_NONE);
        s3c_gpio_cfgpin(S3C2410_GPB(0),S3C2410_GPB0_TOUT0);
    }
    return brightness;
}
static void s3c2416_backlight_exit(struct device *dev)
{
    gpio_direction_output(S3C2410_GPB(0),0);
}
static struct platform_pwm_backlight_data backlight_data = 
{
    .max_brightness= 100,
    .dft_brightness= 50,
    .enable_gpio    = -1,
    .init           = s3c2416_backlight_init,
    .notify         = s3c2416_backlight_notify,
    .exit           = s3c2416_backlight_exit,
};
static struct platform_device s3c2416_backlight = 
{
    .name= "pwm-backlight",
    .dev = {
          .parent= &samsung_device_pwm.dev,
          .platform_data= &backlight_data,
    },
    .id   = -1,
};
static struct pwm_lookup s3c2416_pwm_lookup[] = {
    PWM_LOOKUP("samsung-pwm",0, "pwm-backlight", NULL, 36296, PWM_POLARITY_NORMAL),
};

在板级初始化函数home2416_machine_init ()中把pwm背光映射到pwm设备表中pwm_add_table(s3c2416_pwm_lookup, ARRAY_SIZE(s3c2416_pwm_lookup))，在static struct platform_device *home2416_devices[]板级平台设备列表中加入&s3c2416_backlight，使背光设备能够注册到内核中。

修改drivers\tty\vt\vt.c，禁止lcd开机一段时间后自动关屏:

static int blankinterval = 0;

修改drivers/video/console/fbcon.c，禁止光标闪烁:

static int fbcon_cursor_noblink = 1;

2、内核配置

Linux配置支持lcd设备驱动，选中 Device Drivers->Graphics support->Frame buffer Devices->Samsumg S3C framebuffer support ：

Linux配置支持lcd背光驱动，选中DeviceDrivers->Graphics support->Backlight & LCD device support->Generic PWM based Backlight Driver。

Linux配置开机logo，DeviceDrivers->Graphics support->Bootup logo->Standard 224-color Linux logo。

3、lcd测试

cat /proc/devices可以知道lcd主设备号为29，次设备号为0，在/dev目录中创建fb0设备文件。

mknod  /dev/fb0  c  29  0

lcd显示黑屏。

mknod  /dev/zero  c  1  5
dd if=/dev/zero of=/dev/fb0

4、应用编程

应用程序可以通过设备文件访问lcd，lcd纯色显示应用测试代码lcd_test.c如下。

#include "fcntl.h"
#include "unistd.h"
#include "stdio.h"
#include "stdlib.h"
#include "sys/mman.h"
void screen_clear(unsigned short*ppixel, unsigned short color)
{
    int i;
    for(i=0; i<800*480; i++)
        ppixel[i]= color;
}
int main(void)
{
       unsignedshort colors[] = {0xffff, 0x0000, 0xf800,
              0x07e0,0x001f, 0xffe0, 0xf81f, 0x7ff};
       int screen_size;
       int fd;
       int index;
       unsignedshort *ppixel;
       fd= open("/dev/fb0", O_RDWR);
       if(fd == -1) {
            printf("Openframebuffer failed\n");
            exit(1);
       }
       screen_size= 800*480*2;
       ppixel=(unsigned short *)mmap(0, screen_size,
              PROT_READ|PROT_WRITE,MAP_SHARED, fd,0);
       if(ppixel == (unsigned short *)-1) {
              printf("Mapframebuffer failed\n");
              exit(1);
       }
       while(1) {
              screen_clear(ppixel,colors[index]);
              index++;
              if(index >= sizeof(colors)/sizeof(colors[0]))
                index= 0;
              sleep(2);
       }
       umap(ppixel,screen_size);
       close(fd);
       return0;
}

用arm-linux-gcc静态编译，使之生成arm cpu可执行的指令，并且可脱离任何库独立运行：

arm-linux-gcc -static -o lcd_test

lcd_test.c，生成lcd_test可执行文件。复制可执行文件到根文件系统，目标板启动后在目录输入./lcd_test即可执行。

5、附录