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。