linux lcd设备驱动剖析四

mutougeda · 发表于 2020-4-26 10:00

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本帖最后由 mutougeda 于 2020-4-26 10:01 编辑

在“linux lcd设备驱动剖析二”文章中，我们详细分析了s3c24xxfb_probe函数。

文章链接：https://www.eda365.com/thread-361614-1-1.html

s3c2410fb.c中s3c24xxfb_probe是非常重要的函数之一，但仅仅分析probe函数，貌似感觉有点不够过瘾，貌似缺少分析了一个非常重要的成员。在probe函数中有一句：fbinfo->fbops = &s3c2410fb_ops;

static struct fb_ops s3c2410fb_ops = {
      .owner                      = THIS_MODULE,
      .fb_check_var       = s3c2410fb_check_var,             //设置可变参数
      .fb_set_par             = s3c2410fb_set_par,             //设置固定参数及lcdcon寄存器
      .fb_blank             = s3c2410fb_blank,                      //设置是否使能LCD控制器
      .fb_setcolreg       = s3c2410fb_setcolreg,             //设置RGB颜色，实现伪颜色表
      .fb_fillrect       = cfb_fillrect,                               //画一个矩形
      .fb_copyarea       = cfb_copyarea,                               //Copy data from area to another
      .fb_imageblit       = cfb_imageblit,                      //Draws a image to the display
};
一、s3c2410fb_check_var函数主要根据tq2440_lcd_cfg实例来设置fb_info结构体的可变参数

fb_var_screeninfo结构体各个成员，如xres、yres、bits_per_pixel、height、width 等等，具体分析如下：

/* 此函数的主要功能是设置可变参数var  */
static int s3c2410fb_check_var(struct fb_var_screeninfo *var,
                           struct fb_info *info)
{
      struct s3c2410fb_info *fbi = info->par;

      /* platform_data就是tq2440_fb_info结构体实例 */
      struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;
      struct s3c2410fb_display *display = NULL;

      /* 在tq2440_fb_info实例里，displays = tq2440_lcd_cfg，default_display = 0 */
      struct s3c2410fb_display *default_display = mach_info->displays +
                                                mach_info->default_display;

      /* 在tq2440_fb_info实例里,type = S3C2410_LCDCON1_TFT */
      int type = default_display->type;
      unsigned i;

      dprintk("check_var(var=%p, info=%p)\n", var, info);

      /* validate x/y resolution */
      /* choose default mode if possible */

      /* 如果参数都等于tq2440_fb_info实例里的参数
      * 那么赋值给display，此时display指向tq2440_fb_info实例
      */
      if (var->yres == default_display->yres &&
         var->xres == default_display->xres &&
         var->bits_per_pixel == default_display->bpp)
            display = default_display;

      /* 否则从tq2440_fb_info结构体实例中循环匹配,num_displays = 1 */
      else
            for (i = 0; i < mach_info->num_displays; i++)
                     if (type == mach_info->displays.type &&
                        var->yres == mach_info->displays.yres &&
                        var->xres == mach_info->displays.xres &&
                        var->bits_per_pixel == mach_info->displays.bpp) {
                              display = mach_info->displays + i;
                              break;
                     }

      /* 如果匹配不成功，display = NULL 则错误 */
      if (!display) {
            dprintk("wrong resolution or depth %dx%d at %d bpp\n",
                     var->xres, var->yres, var->bits_per_pixel);
            return -EINVAL;
      }

      /* it is always the size as the display */
      /* 找到匹配的display后，将实例中的可变参数赋值 */
      var->xres_virtual       = display->xres;
      var->yres_virtual       = display->yres;
      var->height                = display->height;
      var->width                      = display->width;

      /* copy lcd settings */
      var->pixclock                = display->pixclock;
      var->left_margin       = display->left_margin;
      var->right_margin       = display->right_margin;
      var->upper_margin       = display->upper_margin;
      var->lower_margin       = display->lower_margin;
      var->vsync_len             = display->vsync_len;
      var->hsync_len                = display->hsync_len;

      fbi->regs.lcdcon5       = display->lcdcon5;
      /* set display type */
      fbi->regs.lcdcon1       = display->type;

      var->transp.offset       = 0;
      var->transp.length       = 0;
      /* set r/g/b positions */
      switch (var->bits_per_pixel) {
      case 1:
      case 2:
      case 4:
            var->red.offset             = 0;
            var->red.length             = var->bits_per_pixel;
            var->green                      = var->red;
            var->blue                      = var->red;
            break;
      ......

      /* TQ2440的LCD就是采用这种模式 */
      case 32:
            /* 24 bpp 888 and 8 dummy */
            var->red.length             = 8;
            var->red.offset             = 16;
            var->green.length       = 8;
            var->green.offset       = 8;
            var->blue.length       = 8;
            var->blue.offset       = 0;
            break;
      }
      return 0;
}
tq2440_lcd_cfg实例在arch/ARM/mach-s3c2440/mach-tq2440.c中定义

/* LCD driver info */
/* tq2440_lcd_cfg在tq2440_fb_info中被设置 */
static struct s3c2410fb_display tq2440_lcd_cfg __initdata = {
      .lcdcon5       = S3C2410_LCDCON5_FRM565 |
                        S3C2410_LCDCON5_INVVLINE |
                        S3C2410_LCDCON5_INVVFRAME |
                        S3C2410_LCDCON5_PWREN |
                        S3C2410_LCDCON5_HWSWP,
      .type             = S3C2410_LCDCON1_TFT,

      ......

/* TQ(LCD W4.3)的配置,config_EmbedSky_W43:CONFIG_FB_S3C24X0_TFT480272=y */
#elif defined(CONFIG_FB_S3C24X0_TFT480272)
      .width                = 480,
      .height                = 272,

      .pixclock       = 40000, /* HCLK 100 MHz, divisor 1 */

      /* VCLK=HCLK/[(CLKVAL+1)x2]，HCLK = 100MHz
      * 根据LCD手册"WXCAT43-TG6#001_V1.0.pdf"的第22页可得,VCLK = 10MHz
      * 即10 = 100/[(CLKVAL+1)x2]，可得CLKVAL = 4
   */
      .setclkval       = 0x4,
      .xres                = 480,
      .yres                = 272,
      .bpp                = 16,

      /* 为什么是这样?参考linux/Documentation/fb/framebuffer.txt */
      .left_margin  = 19,       /* 左边沿  : for HFPD*/
      .right_margin = 10,       /* 右边沿  : for HBPD*/
      .hsync_len       = 30,       /* 水平同步: for HSPW*/
      .upper_margin = 4,       /* 上边沿  : for VFPD*/
      .lower_margin = 2,       /* 下边沿  : for VBPD*/
      .vsync_len       = 8,       /* 垂直同步: for VSPW*/

      ......
};
二、s3c2410fb_set_par函数先根据var->bits_per_pixel来选择fix.visual，这里bits_per_pixel = 32，

故fix.visual = FB_VISUAL_TRUECOLOR，然后计算一行的字节数，最后调用s3c2410fb_activate_var

函数来激活LCD控制器，即设置各个lcdcon寄存器。

static int s3c2410fb_set_par(struct fb_info *info)
{
      /* 获得刚被s3c2410fb_check_var函数设置过的var */
      struct fb_var_screeninfo *var = &info->var;

      switch (var->bits_per_pixel) {
      case 32:
      case 16:
      case 12:
            info->fix.visual = FB_VISUAL_TRUECOLOR;             /* 真彩色 */
            break;
      case 1:
            info->fix.visual = FB_VISUAL_MONO01;
            break;
      default:
            info->fix.visual = FB_VISUAL_PSEUDOCOLOR;
            break;
      }

      /* 一行的字节数 = x*bpp/8 = 480*32/8 = 480*4 */
      info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;

      /* activate this new configuration */
      s3c2410fb_activate_var(info);

      return 0;
}
s3c2410fb_activate_var函数先调用s3c2410fb_calc_pixclk函数来计算LCD时钟频率，然后调用s3c2410fb_calculate_tft_lcd_regs函数来设置lcdcon1~lcdcon5，然后调用writel函数将前面s3c2410fb_calculate_tft_lcd_regs函数设置好的lcdconx写入对应寄存器，接着调用s3c2410fb_set_lcdaddr函数来设置LCDSADDR1、LCDSADDR2、LCDSADDR3寄存器，也就是将之前在probe函数通过s3c2410fb_map_video_memory-->dma_alloc_writecombine函数分配好的“显存”告诉LCD控制器，最后使能LCD控制器。
static void s3c2410fb_activate_var(struct fb_info *info)
{
      /* 在framebuffer_alloc函数里info->par指向了额外多申请
      * 内存空间的首地址,即info->par指向s3c2410fb_info结构体
      */
      struct s3c2410fb_info *fbi = info->par;
      void __iomem *regs = fbi->io;             /* IO基地址 */

      /* 设置显示模式为: TFT LCD panel */
      int type = fbi->regs.lcdcon1 & S3C2410_LCDCON1_TFT;

      /* 通过probe函数后platform_data指向tq2440_fb_info结构体实例 */
      struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;
      struct s3c2410fb_display *default_display = mach_info->displays +
                                                mach_info->default_display;
      struct fb_var_screeninfo *var = &info->var;

      /* 计算LCD时钟频率, 在mach_tq2440.c里 pixclock = 40000 */
      int clkdiv = s3c2410fb_calc_pixclk(fbi, var->pixclock) / 2;

      dprintk("%s: var->xres  = %d\n", __func__, var->xres);
      dprintk("%s: var->yres  = %d\n", __func__, var->yres);
      dprintk("%s: var->bpp = %d\n", __func__, var->bits_per_pixel);

      if (type == S3C2410_LCDCON1_TFT) {
            s3c2410fb_calculate_tft_lcd_regs(info, &fbi->regs);
            --clkdiv;
            if (clkdiv < 0)
                     clkdiv = 0;
      } else {
            s3c2410fb_calculate_stn_lcd_regs(info, &fbi->regs);
            if (clkdiv < 2)
                     clkdiv = 2;
      }

//       fbi->regs.lcdcon1 |=  S3C2410_LCDCON1_CLKVAL(clkdiv);
      fbi->regs.lcdcon1 |=  S3C2410_LCDCON1_CLKVAL(default_display->setclkval);

      /* write new registers */

      dprintk("new register set:\n");
      dprintk("lcdcon[1] = 0x%08lx\n", fbi->regs.lcdcon1);
      dprintk("lcdcon[2] = 0x%08lx\n", fbi->regs.lcdcon2);
      dprintk("lcdcon[3] = 0x%08lx\n", fbi->regs.lcdcon3);
      dprintk("lcdcon[4] = 0x%08lx\n", fbi->regs.lcdcon4);
      dprintk("lcdcon[5] = 0x%08lx\n", fbi->regs.lcdcon5);

      /* 禁止视频输出,禁止LCD控制信号 */
      writel(fbi->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID,
            regs + S3C2410_LCDCON1);

      /* 将前面s3c2410fb_calculate_tft_lcd_regs函数设置好的lcdconx写入对应寄存器 */
      writel(fbi->regs.lcdcon2, regs + S3C2410_LCDCON2);
      writel(fbi->regs.lcdcon3, regs + S3C2410_LCDCON3);
      writel(fbi->regs.lcdcon4, regs + S3C2410_LCDCON4);
      writel(fbi->regs.lcdcon5, regs + S3C2410_LCDCON5);

      /* set lcd address pointers */
      s3c2410fb_set_lcdaddr(info);

      /* 最后使能LCD控制器，即使能视频输出 */
      fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID,
      writel(fbi->regs.lcdcon1, regs + S3C2410_LCDCON1);
}
s3c2410fb_calculate_tft_lcd_regs函数比较简单这里就不分析了，这里只分析s3c2410fb_set_lcdaddr函数

static void s3c2410fb_set_lcdaddr(struct fb_info *info)
{
      unsigned long saddr1, saddr2, saddr3;
      struct s3c2410fb_info *fbi = info->par;
      void __iomem *regs = fbi->io;

      /* LCDSADDR1 = 帧缓冲区起始地址再右移1位 */
      saddr1  = info->fix.smem_start >> 1;

      /* LCDSADDR2 = 帧缓冲区结束地址再右移1位 */
      saddr2  = info->fix.smem_start;
      saddr2 += info->fix.line_length * info->var.yres;  /* 帧缓冲区大小 */
      saddr2 >>= 1;

      /* LCDSADDR3 = 一行的长度，单位为2字节 */
      saddr3 = S3C2410_OFFSIZE(0) |
               S3C2410_PAGEWIDTH((info->fix.line_length / 2) & 0x3ff);

      dprintk("LCDSADDR1 = 0x%08lx\n", saddr1);
      dprintk("LCDSADDR2 = 0x%08lx\n", saddr2);
      dprintk("LCDSADDR3 = 0x%08lx\n", saddr3);

      writel(saddr1, regs + S3C2410_LCDSADDR1);
      writel(saddr2, regs + S3C2410_LCDSADDR2);
      writel(saddr3, regs + S3C2410_LCDSADDR3);
}
三、s3c2410fb_setcolreg函数主要通过red,green,blue三原色构造出val，然后再将val写入pseudo_palette假调色板中。
static int s3c2410fb_setcolreg(unsigned regno,
                           unsigned red, unsigned green, unsigned blue,
                           unsigned transp, struct fb_info *info)
{
      struct s3c2410fb_info *fbi = info->par;
      void __iomem *regs = fbi->io;
      unsigned int val;

      /* TQ2440的LCD是FB_VISUAL_TRUECOLOR，即TFT */
      switch (info->fix.visual) {
      case FB_VISUAL_TRUECOLOR:
            /* true-colour, use pseudo-palette */
            if (regno < 16) {
                     u32 *pal = info->pseudo_palette;

                     /* 用red,green,blue三原色构造出val */
                     val  = chan_to_field(red, &info->var.red);
                     val |= chan_to_field(green, &info->var.green);
                     val |= chan_to_field(blue,  &info->var.blue);

                     pal[regno] = val;
            }
            break;
      ......

      default:
            return 1;       /* unknown type */
      }
      return 0;
}
chan_to_field 函数如下，将具体的RGB数据代入就比较容易理解这个函数了，相应的var.red、var.green、var.blue在s3c2410fb_check_var函数的最后面有设置。

static inline unsigned int chan_to_field(unsigned int chan,
                                       struct fb_bitfield *bf)
{
      chan &= 0xffff;
      chan >>= 16 - bf->length;
      return chan << bf->offset;
}
s3c2410fb_check_var函数设置rgb的部分代码，这里省略了大部分源码，为的是方便参考。

static int s3c2410fb_check_var(struct fb_var_screeninfo *var,
                           struct fb_info *info)
{
      .......
      /* set r/g/b positions */
      switch (var->bits_per_pixel) {
      .......
      /* TQ2440的LCD就是采用这种模式 */
      case 32:
            /* 24 bpp 888 and 8 dummy */
            var->red.length             = 8;
            var->red.offset             = 16;
            var->green.length       = 8;
            var->green.offset       = 8;
            var->blue.length       = 8;
            var->blue.offset       = 0;
            break;
      }
      return 0;
}
而cfb_fillrect、cfb_copyarea、cfb_imageblit是通用的函数，不用驱动工程师去理会，只需要在加载lcd驱动时，将其对应的模块加载，而要加载模块，必须在编译内核后，再执行make modules，这样就可以得到相应的cfb*.ko了。
到这里s3c2410fb.c内核自带的lcd驱动基本剖析完毕，这里总结一下难点：
一、内核自带的lcd驱动是以平台驱动设备模型来编写的，难点不在框架，框架其实很简单，

1、分配一个fb_info结构体；

2、设置 fb_info结构体；

3、注册；

4、硬件相关的设置

二、好啦，难点就是如何设置fb_info结构体，而fb_info结构体成员那么多，是不每个成员都要一一设置呢？当然不是，

主要设置fb_info结构体的固定参数 fb_fix_screeninfo结构体和可变参数fb_var_screeninfo结构体，还有就是硬件相关

的设置，比如lcd时序参数的设置，也就是要设置lcdcon1~lcdcon5，lcdaddr1~lcdaddr3各个寄存器。

NNNei256 · 发表于 2020-4-26 14:11

linux lcd设备驱动剖析四

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