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https://blog.csdn.net/huangweiqing80/article/details/82990736
为更好的了解Linux LCD子系统，我们先来看一下Linux LCD裸机驱动程序是怎么写的？
1.LCD裸机思维导图
2LCD裸机驱动
这里以TQ2440显示一张图片为例
#define GPCCON (*(volatile unsigned long *)0x56000020)
#define GPDCON (*(volatile unsigned long *)0x56000030)
#define GPGCON (*(volatile unsigned long *)0x56000060)
#define LCDCON1 (*(volatile unsigned long *)0x4D000000)
#define LCDCON2 (*(volatile unsigned long *)0x4D000004)
#define LCDCON3 (*(volatile unsigned long *)0x4D000008)
#define LCDCON4 (*(volatile unsigned long *)0x4D00000C)
#define LCDCON5 (*(volatile unsigned long *)0x4D000010)
#define LCDSADDR1 (*(volatile unsigned long *)0x4D000014)
#define LCDSADDR2 (*(volatile unsigned long *)0x4D000018)
#define LCDSADDR3 (*(volatile unsigned long *)0x4D00001C)
#define TPAL (*(volatile unsigned long *)0x4D000050)
#define VSPW 9
#define VBPD 1
#define LINEVAL 271
#define VFPD 1
#define CLKVAL 4 //10 = 100/((CLKVAL+1)*2)
#define HSPW 40
#define HBPD 1
#define HOZVAL 479
#define HFPD 1
unsigned short LCDBUFFER[272][480];
typedef unsigned int U32;
typedef unsigned short U16;
typedef unsigned char U8;
void lcd_port_init()
{
GPDCON = 0xaaaaaaaa;
GPCCON = 0xaaaaaaaa;
}
void lcd_control_init()
{
LCDCON1 = (CLKVAL<<8)|(0x3<<5)|(0xc<<1)|(0<<0);
LCDCON2 = (VBPD<<24)|(LINEVAL<<14)|(VFPD<<6)|(VSPW);
LCDCON3 = (HBPD<<19)|(HOZVAL<<8)|(HFPD);
LCDCON4 = (HSPW);
LCDCON5 = (1<<11)|(1<<9)|(1<<8);
LCDSADDR1 = (((U32)LCDBUFFER>>22)<<21) | (((U32)LCDBUFFER>>1)&0x1fffff);
LCDSADDR2 = (((U32)LCDBUFFER+272*480*2)>>1)&0x1fffff;
LCDSADDR3 = (0<<11) | (480*2/2);
TPAL = 0;
}
void lcd_init()
{
lcd_port_init();
lcd_control_init();
//打开LCD电源
GPGCON |= (0x3<<8);
LCDCON5 |= (1<<3);
LCDCON1 |= 1;
}
void point(unsigned int x,unsigned int y,unsigned int color)
{
unsigned int red, green, blue;
red = (color>>19) & 0x1f;
green = (color>>10) & 0x3f;
blue = (color>>3) & 0x1f;
LCDBUFFER[y][x] = (unsigned short)((red<<11)|(green<<5)|blue);
}
void Paint_Bmp(U16 x0,U16 y0,U16 wide,U16 high,const U8 *bmp)
{
U16 x,y;
U16 c;
U32 p = 0;
for( y = y0 ; y < y0+high ; y++ )
{
for( x = x0 ; x < x0+wide ; x++ )
{
c = bmp[p] | (bmp[p+1]<<8) ;
if ( ( x < 480) && ( y < 272) )
LCDBUFFER[y][x] = c ;
p = p + 2 ;
}
}
}
void clearSrc(unsigned int color)
{
TPAL = (1<<24)|(color&0xffffff);
}
extern unsigned char bmp[90200];
void lcd_test()
{
int x;
for(x=0;x<480;x++)
point(x++,150,0xff0000);
Paint_Bmp(0,0,220,220,bmp);
clearSrc(0xff0000);
}
关于Linux LCD驱动程序的分析：LINUX下的LCD子系统分析
通过这篇文章我大概讲一下我的个人理解：
- LCD子系统是通过平台设备驱动模型来注册的，他有device和driver两个部分。
- framebuffer是为了封装LCD，提供统一的用户空间环境，这样在用户空间显示图片和读取图片就可以通过/dev/fb节点来操作
- framebuffer是在LCD driver 的probe函数中进行初始化和注册的
- probe函数中的下面函数的个人理解
4.1 s3c2410fb_map_video_memory
分配帧缓冲内存，unsigned short LCDBUFFER[272][480];
4.2 s3c2410fb_init_registers
设置引脚类型，对应LCD裸机中的引脚初始化 lcd_port_init
4.3 s3c2410fb_set_par
设置LCD控制器寄存器，对应LCD裸机中的时序初始化lcd_control_init
5.关于fb_info 结构体，我家里中文解释的成员很重要
struct fb_info {
atomic_t count;
int node;
int flags;
struct mutex lock; /* Lock for open/release/ioctl funcs */
struct mutex mm_lock; /* Lock for fb_mmap and smem_* fields */
struct fb_var_screeninfo var; /* Current var */ 像素点等设置
struct fb_fix_screeninfo fix; /* Current fix */
struct fb_monspecs monspecs; /* Current Monitor specs */
struct work_struct queue; /* Framebuffer event queue */
struct fb_pixmap pixmap; /* Image hardware mapper */
struct fb_pixmap sprite; /* Cursor hardware mapper */
struct fb_cmap cmap; /* Current cmap */
struct list_head modelist; /* mode list */
struct fb_videomode *mode; /* current mode */
#ifdef CONFIG_FB_BACKLIGHT
/* assigned backlight device */
/* set before framebuffer registration,
remove after unregister */
struct backlight_device *bl_dev;
/* Backlight level curve */
struct mutex bl_curve_mutex;
u8 bl_curve[FB_BACKLIGHT_LEVELS];
#endif
#ifdef CONFIG_FB_DEFERRED_IO
struct delayed_work deferred_work;
struct fb_deferred_io *fbdefio;
#endif
struct fb_ops *fbops;
struct device *device; /* This is the parent */
struct device *dev; /* This is this fb device */
int class_flag; /* private sysfs flags */
#ifdef CONFIG_FB_TILEBLITTING
struct fb_tile_ops *tileops; /* Tile Blitting */
#endif
char __iomem *screen_base; /* Virtual address */ 帧缓冲起始地址
unsigned long screen_size; /* Amount of ioremapped VRAM or 0 */
void *pseudo_palette; /* Fake palette of 16 colors */
#define FBINFO_STATE_RUNNING 0
#define FBINFO_STATE_SUSPENDED 1
u32 state; /* Hardware state i.e suspend */
void *fbcon_par; /* fbcon use-only private area */
/* From here on everything is device dependent */
void *par;
/* we need the PCI or similar aperture base/size not
smem_start/size as smem_start may just be an object
allocated inside the aperture so may not actually overlap */
struct apertures_struct {
unsigned int count;
struct aperture {
resource_size_t base;
resource_size_t size;
} ranges[0];
} *apertures;
};
上面讲的是三星平台的LCD子系统架构，其他平台的架构会略有不同，但都大同小异，下面我们再来看一下MTK平台的LCD子系统
MTK LCD 驱动过程详解
这边我也补充一下：
- MTK 的LCD子系统同样也是通过平台设备驱动模型来驱动的，他同样也有device 和driver两部分，文中只讲了plateform_driver部分，plateform_device部分在source/mediatek/platform/mt6572/kernel/core/mt_devs.c
__init int mt_board_init(void)
{
...
retval = platform_device_register(&mt6575_device_fb);
...
}
static struct platform_device mt6575_device_fb = {
.name = "mtkfb",
.id = 0,
.num_resources = ARRAY_SIZE(resource_fb),
.resource = resource_fb,
.dev = {
.dma_mask = &mtkfb_dmamask,
.coherent_dma_mask = 0xffffffff,
},
};
知道了MTK整个LCD子系统的架构，我们再来看MTK LCM的移植就很清楚了
1. LCD
1.1怎样新建一个LCD驱动
LCD模组主要包括LCD显示屏和驱动IC。比如LF040DNYB16a模组的驱动IC型号为NT35510。要在MT577平台上新建这个lcd的驱动，步骤如下：
A. 新建文件夹nt35510：
\mediatek\custom\common\kernel\lcm\nt35510
\mediatek\custom\common\lk\lcm\nt35510 //\mediatek\custom\common\uboot\lcm\nt35510
B.修改\mediatek\custom\common\kernel\lcm\mt65xx_lcm_list.c, 在lcm_driver_list [ lcm_count ] 中增加nt35510_lcm_drv。
C.打开mediatek\config\ginwave73_gb\ProjectConfig.mk：
BUILD_LK=yes //BUILD_UBOOT=yes
BOOT_LOGO=wsvganl
CUSTOM_KERNEL_LCM = nt35510
CUSTOM_LK_LCM= nt35510 // CUSTOM_UBOOT_LCM =nt35510
LCM_WIDTH=600
LCM_HEIGHT=1024
驱动文件移植原则：
根据具体平台，填充对应的函数，不能直接复制整个文件，避免不必要编译和接口错误。
其他平台（如RK，IMX等）的LCM移植会不同，但是我们可以通过分析LCD子系统的架构便能很清晰的知道移植需要移植哪些东西