linux lcd设备驱动剖析四

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：http://blog.csdn.net/lwj103862095/article/details/18189765

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[i].type &&
                 var->yres == mach_info->displays[i].yres &&
                 var->xres == mach_info->displays[i].xres &&
                 var->bits_per_pixel == mach_info->displays[i].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。