【驱动】09.LCD驱动

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LCD驱动

硬件原理

MCU常用的8080接口LCD模组（Framebuffer内存+LCD控制器+LCD屏幕都是外面的）

MPU常用的TFT RGB接口（Framebuffer内存+LCD控制器集成在芯片里面）

MIPI标准

对于LCD，MIPI接口可以分为3类：

• MIPI-DBI (Display Bus Interface)

  • 既然是Bus(总线)，就是既能发送数据，也能发送命令，常用的8080接口就属于DBI接口。

  • Type B (i-80 system), 8-/9-/16-/18-/24-bit bus

  • Type C (Serial data transfer interface, 3/4-line SPI)

• MIPI-DPI (Display Pixel Interface)

  • Pixel(像素)，强调的是操作单个像素，在MPU上的LCD控制器就是这种接口

  • Supports 24 bit/pixel (R: 8-bit, G: 8-bit, B: 8-bit)

  • Supports 18 bit/pixel (R: 6-bit, G: 6-bit, B: 6-bit)

  • Supports 16 bit/pixel (R: 5-bit, G: 6-bit, B: 5-bit)

• MIPI-DSI (Display Serial Interface)

  • Serial，相比于DBI、DPI需要使用很多接口线，DSI需要的接口线大为减少
  • Supports one data lane/maximum speed 500Mbps
  • Supports DSI version 1.01
  • Supports D-PHY version 1.00

应用编程

结合APP分析LCD驱动程序

1. open

app:  open("/dev/fb0", ...)   主设备号: 29, 次设备号: 0
--------------------------------------------------------------
kernel:
         fb_open   // fbmem.c
         	struct fb_info *info;
         	info = get_fb_info(fbidx);
			
			if (info->fbops->fb_open) {
				res = info->fbops->fb_open(info,1);   // 硬件相关的驱动
				if (res)
					module_put(info->fbops->owner);
			}         	

2. 获得可变信息(含有分辨率等)

app:  	ioctl(fd, FBIOGET_VSCREENINFO, &fb_info->var);
-------------------------------------------------------------------------
kernel:
         fb_ioctl   // fbmem.c
         	struct fb_info *info = file_fb_info(file);

         	do_fb_ioctl(info, cmd, arg);
         		var = info->var;     // 硬件相关的驱动设置的
         		ret = copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;

3. 获得固定信息(含有显存信息)

app:  	ioctl(fd, FBIOGET_FSCREENINFO, &fb_info->fix);
-------------------------------------------------------------------------
kernel:
         fb_ioctl   // fbmem.c
         	struct fb_info *info = file_fb_info(file);

         	do_fb_ioctl(info, cmd, arg);
         		fix = info->fix;     // 硬件相关的驱动设置的
         		ret = copy_to_user(argp, &fix, sizeof(fix)) ? -EFAULT : 0;

4. mmap

app：void *ptr = mmap(0,
			fb_info->var.yres_virtual * fb_info->fix.line_length,
			PROT_WRITE | PROT_READ,
			MAP_SHARED, fd, 0);
-------------------------------------------------------------------------
kernel:
         fb_mmap   // fbmem.c
         	struct fb_info *info = file_fb_info(file);

         	start = info->fix.smem_start;
         	len = info->fix.smem_len;
         	return vm_iomap_memory(vma, s