framebuffer-Linux驱动分析之Framebuffer驱动

Framebuffer截图_framebuffer_Framebuffer画布

前言

前面我们了解了LCD的基本架构《》，接下来我们拿个具体的实例来分析分析。这样可以了解其大概是如何使用和工作的。

FrameBuffer驱动分析

内核版本：4.20

芯片平台：s3c2410

依然是使用之前的方式进行分析，大部分内容在注释。

(1)装载和卸载函数

static struct platform_driver s3c2410fb_driver = {  .probe    = s3c2410fb_probe,  .remove    = s3c2410fb_remove,  .suspend  = s3c2410fb_suspend,  .resume    = s3c2410fb_resume,  .driver    = {    .name  = "s3c2410-lcd",  },};
int __init s3c2410fb_init(void){  int ret = platform_driver_register(&s3c2410fb_driver);  return ret;}
static void __exit s3c2410fb_cleanup(void){  platform_driver_unregister(&s3c2410fb_driver);}
module_init(s3c2410fb_init);module_exit(s3c2410fb_cleanup);

上面比较简单，就是注册一个platform_driver, 控制器一般都是使用platform总线。

(2)probe()

static int s3c2410fb_probe(struct platform_device *pdev){  return s3c24xxfb_probe(pdev, DRV_S3C2410);}
static int s3c24xxfb_probe(struct platform_device *pdev,         enum s3c_drv_type drv_type){  struct s3c2410fb_info *info;  struct s3c2410fb_display *display;  struct fb_info *fbinfo;  struct s3c2410fb_mach_info *mach_info;  struct resource *res;  int ret;  int irq;  int i;  int size;  u32 lcdcon1;    //获取板子配置信息  mach_info = dev_get_platdata(&pdev->dev);    //省略......   //display包含了屏幕的分辨率信息等  display = mach_info->displays + mach_info->default_display;   //获取中断号  irq = platform_get_irq(pdev, 0);
   //分配一个fb_info  fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);    //保存fbinfo到driver data  platform_set_drvdata(pdev, fbinfo);
  info = fbinfo->par;  info->dev = &pdev->dev;  info->drv_type = drv_type;    //获取IO资源并申请  res = platform_get_resource(pdev, IORESOURCE_MEM, 0);  size = resource_size(res);  info->mem = request_mem_region(res->start, size, pdev->name);
    //映射为虚拟地址  info->io = ioremap(res->start, size);   //获取中断基地址  info->irq_base = info->io + S3C2410_LCDINTBASE;
  strcpy(fbinfo->fix.id, driver_name);
  //操作寄存器，停止LCDC输出  lcdcon1 = readl(info->io + S3C2410_LCDCON1);  writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, info->io + S3C2410_LCDCON1);   //初始化固定参数  fbinfo->fix.type      = FB_TYPE_PACKED_PIXELS;  fbinfo->fix.type_aux      = 0;  fbinfo->fix.xpanstep      = 0;  fbinfo->fix.ypanstep      = 0;  fbinfo->fix.ywrapstep      = 0;  fbinfo->fix.accel      = FB_ACCEL_NONE;   //初始化可变参数  fbinfo->var.nonstd      = 0;  fbinfo->var.activate      = FB_ACTIVATE_NOW;  fbinfo->var.accel_flags     = 0;  fbinfo->var.vmode      = FB_VMODE_NONINTERLACED;   //设置操作函数  fbinfo->fbops        = &s3c2410fb_ops;  fbinfo->flags        = FBINFO_FLAG_DEFAULT;  fbinfo->pseudo_palette      = &info->pseudo_pal;   //清除画板  for (i = 0; i < 256; i++)    info->palette_buffer[i] = PALETTE_BUFF_CLEAR;   //申请中断  ret = request_irq(irq, s3c2410fb_irq, 0, pdev->name, info);    //获取时钟并使能  info->clk = clk_get(NULL, "lcd");  clk_prepare_enable(info->clk);
  usleep_range(1000, 1100);
  info->clk_rate = clk_get_rate(info->clk);
  /* 计算显示所需分配的内存大小 */  for (i = 0; i num_displays; i++) {    unsigned long smem_len = mach_info->displays[i].xres;
    smem_len *= mach_info->displays[i].yres;    smem_len *= mach_info->displays[i].bpp;    smem_len >>= 3;    if (fbinfo->fix.smem_len < smem_len)      fbinfo->fix.smem_len = smem_len;  }
  /* 初始化显存，这里面设置了DMA */  ret = s3c2410fb_map_video_memory(fbinfo);   //根据屏幕信息初始化fbinfo中的可变参数  fbinfo->var.xres = display->xres;  fbinfo->var.yres = display->yres;  fbinfo->var.bits_per_pixel = display->bpp;  //初始化LCDC相关寄存器  s3c2410fb_init_registers(fbinfo);
   //注册framebuffer  ret = register_framebuffer(fbinfo);
  return 0;
}

上面省略了一些错误判断。

上面总结下来就两个部分：

1. 根据屏幕信息填充fb_info, 然后调用register_framebuffer进行注册

2. LCDC相对应的寄存器的配置(硬件平台相关的)

(3)各种操作屏幕的函数

static struct fb_ops s3c2410fb_ops = {  .owner    = THIS_MODULE,  .fb_check_var  = s3c2410fb_check_var, //检查可变参数合法性  .fb_set_par  = s3c2410fb_set_par, //设置可变参数  .fb_blank  = s3c2410fb_blank, //设置开关屏  .fb_setcolreg  = s3c2410fb_setcolreg, //设置颜色寄存器     //下面三个都是使用内核自带的函数  .fb_fillrect  = cfb_fillrect, //绘制矩形  .fb_copyarea  = cfb_copyarea, //区域拷贝  .fb_imageblit  = cfb_imageblit,//绘制位图};

简单看几个函数，其实就是对寄存器的操作。

static int s3c2410fb_set_par(struct fb_info *info){    //设置参数信息  struct fb_var_screeninfo *var = &info->var;      switch (var->bits_per_pixel) {  case 32:  case 16:  case 12:    info->fix.visual = FB_VISUAL_TRUECOLOR;    break;  case 1:    info->fix.visual = FB_VISUAL_MONO01;    break;  default:    info->fix.visual = FB_VISUAL_PSEUDOCOLOR;    break;  }
  info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;    //设置寄存器，该函数中都是寄存器的操作  s3c2410fb_activate_var(info);  return 0;}

static int s3c2410fb_blank(int blank_mode, struct fb_info *info){  struct s3c2410fb_info *fbi = info->par;  void __iomem *tpal_reg = fbi->io;
  dprintk("blank(mode=%d, info=%p)n", blank_mode, info);  tpal_reg += is_s3c2412(fbi) ? S3C2412_TPAL : S3C2410_TPAL;    //根据开关设置寄存器  if (blank_mode == FB_BLANK_POWERDOWN)    s3c2410fb_lcd_enable(fbi, 0);  else    s3c2410fb_lcd_enable(fbi, 1);
  if (blank_mode == FB_BLANK_UNBLANK)    writel(0x0, tpal_reg);  else {    dprintk("setting TPAL to output 0x000000n");    writel(S3C2410_TPAL_EN, tpal_reg);  }
  return 0;}