Linux下的LCD驱动(一)

版权所有，转载必须说明转自 http://my.csdn.net/weiqing1981127 

原创作者：南京邮电大学  通信与信息系统专业 研二 魏清

 

一．LCD屏理论

1.1 LCD屏基本概念

我们知道，诸如PCI、I2C和USB等外围设备总线都来自于系统PC机的南桥，今天我们看到的视频控制器则来自于北桥。LCD主要由TN(扭转向列型)、STN(超扭转向列型)、DSTN(双层超扭曲向列阵)和TFT(薄膜式晶体管型)四种显示器，许多MCU内部直接集成了LCD控制器，通过LCD控制器可以方便地控制STN和TFT屏，其中TFT屏是目前嵌入式系统应用的主流。LCD常的接口类型有RGB、CPU、SPI、MIPI、MDDI、LVDS和VGA。

 

显示标准：VGA(视频图形阵列)是IBM早期提出的显示标准，VGA的分辨率是640x480，而更新标准的SVGA(高级视频图形阵列)和XGA(扩展图形阵列)则支持800x600和1024x768分辨率，嵌入式设备常用分辨率为320x240的QVGA面板。

视频标准：许多接口标准对视频控制器和显示设备的连接做了规定，视频电缆有如下标准，其一，模拟显示器；其二，数字平面显示器，如笔记本的TFT LCD，有LVDS(低电压差分信号)连接器；其三，与DVI(数字视频接口)规范标准兼容的显示器；其四，与HDTV(高清电视)规范兼容的显示器，它使用HDMI(高清多媒体接口)。

LCD常用参数：PPI是每平方英寸所拥有的像素数目，BPP是每个像素使用多少位来表示其颜色。

 

1.2帧缓冲的理解

FrameBuffer又叫帧缓冲，是Linux为操作显示设备提供的一个用户接口，用户应用程序可以通过帧缓冲透明地访问不同类型的显示设备。对于帧缓冲设备，只要在显示缓冲区与显示点对应区域写入颜色值，对应的颜色会自动在屏幕上显示，帧缓冲设备是标准的字符设备，主设备号是29，对应于/dev/fbn设备文件。

在Linux中，帧缓冲可以看成一个内存，既可以向这块内存中写数据，也可以向这个内存中读数据，用户不需要关心物理显存的位置和换页机制，这些都是由帧缓冲设备驱动完成的。帧缓冲区位于Linux内核态地址空间，所以Linux在文件操作file_operations结构中提供了mmap函数，可将缓冲区的物理地址映射到用户空间的一段虚拟地址中，之后用户就可以通过读写这段虚拟地址访问屏幕缓冲区了。帧缓冲驱动的功能就是分配一块内存作显存，然后设置LCD控制器的寄存器，LCD显示器就会不断从显存中获得数据，并显示在LCD屏上。

 

二．Mini2440的X35型LCD移植

先说明下像素时钟pixclock的概念

pixclock=1/dotclock  其中dotclock是视频硬件在显示器上绘制像素的速率

dotclock=(x向分辨率+左空边+右空边+HSYNC长度)* (y向分辨率+上空边+下空边+YSYNC长度)*整屏的刷新率

其中x向分辨率、左空边、右空边、HSYNC长度、y向分辨率、上空边、下空边和YSYNC长度可以在X35LCD说明文档中查到。

整屏的刷新率计算方法如下：

假如我们通过查X35LCD说明文档，知道fclk=6.34MHZ，那么画一个像素需要的时间就是1/6.34us，如果屏的大小是240*320，那么现实一行需要的时间就是240/6.34us，每条扫描线是240，但是水平回扫和水平同步也需要时间，如果水平回扫和水平同步需要29个像素时钟，因此，画一条扫描线完整的时间就是(240+29) /6.34us。完整的屏有320根线，但是垂直回扫和垂直同步也需要时间，如果垂直回扫和垂直同步需要13个像素时钟，那么画一个完整的屏需要(240+29)*(320+13)/6.34us，所以整屏的刷新率就是6.34/((240+29)*(320+13))MHZ

 

下面我们来看看怎么移植LCD驱动，我们的mini2440使用的是X35的LCD屏，根据X35的LCD说明文档，需要在BSP中X35LCD屏的一些参数。

在mach-mini2440.c中添加X35LCD的参数

#if defined(CONFIG_FB_S3C2410_X240320)   //定义X35LCD参数

#define LCD_WIDTH 240   //屏宽

#define LCD_HEIGHT 320  //屏高

#define LCD_PIXCLOCK 170000  //时钟

#define LCD_RIGHT_MARGIN 25    //左边界

#define LCD_LEFT_MARGIN 0    //右边界

#define LCD_HSYNC_LEN 4      //行同步

#define LCD_UPPER_MARGIN 0   //上边界

#define LCD_LOWER_MARGIN 4   //下边界

#define LCD_VSYNC_LEN 9     //帧同步

#define LCD_CON5 (S3C2410_LCDCON5_FRM565 | S3C2410_LCDCON5_INVVDEN | S3C2410_LCDCON5_INVVFRAME | S3C2410_LCDCON5_INVVLINE | S3C2410_LCDCON5_INVVCLK | S3C2410_LCDCON5_HWSWP )

#elif  //定义其他LCD屏参数

#endif

 

好了，我们现在发现要想上面定义的X35LCD的参数正在起作用，必须使得CONFIG_FB_S3C2410_X240320=y；我们需要在/driver/video/Kconfig中定义

config FB_S3C2410_X240320

       boolean "3.5 inch 240X320 LCD(ACX502BMU)"

       depends on FB_S3C2410

       help

         3.5 inch 240X320 LCD(ACX502BMU)

然后我们通过make menuconfig选中"3.5 inch 240X320 LCD(ACX502BMU)"这一选项。

根据我们的X35LCD屏的说明文档，我们已经定义了一些边界参数和同步参数，因为我们的LCD驱动是基于platform总线的，所以需要在这个BSP中添加LCD的平台设备。

struct platform_device s3c_device_lcd = {   //添加LCD平台设备

       .name              = "s3c2410-lcd",       //设备名

       .id            = -1,                

       .num_resources      = ARRAY_SIZE(s3c_lcd_resource),

       .resource         = s3c_lcd_resource,        //资源

       .dev              = {

              .dma_mask           = &s3c_device_lcd_dmamask,

              .coherent_dma_mask   = 0xffffffffUL

       }

};

资源的定义如下

static struct resource s3c_lcd_resource[] = {

       [0] = {                       //内存空间资源

              .start = S3C24XX_PA_LCD,

              .end   = S3C24XX_PA_LCD + S3C24XX_SZ_LCD - 1,

              .flags = IORESOURCE_MEM,

       },

       [1] = {                    //中断资源

              .start = IRQ_LCD,

              .end   = IRQ_LCD,

              .flags = IORESOURCE_IRQ,

       }

 

};

然后我们把s3c_device_lcd放到mini2440_devices[]结构体中，接着调用platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices))将LCD平台设备注册到内核。

对于我们的LCD，需要给这个平台设备添加平台设备数据，通过调用

s3c24xx_fb_set_platdata(&mini2440_fb_info);

static struct s3c2410fb_mach_info mini2440_fb_info __initdata = {

       .displays = &mini2440_lcd_cfg,   //定义s3c2410fb_display数据

       .num_displays       = 1,

       .default_display = 0,

       .gpccon =       0xaa955699,  //GPC端口设置

       .gpccon_mask =  0xffc003cc,

       .gpcup =        0x0000ffff,

       .gpcup_mask =   0xffffffff,

       .gpdcon =       0xaa95aaa1,     //GPD端口设置

       .gpdcon_mask =  0xffc0fff0,

       .gpdup =        0x0000faff,

       .gpdup_mask =   0xffffffff,

       .lpcsel            = 0xf82,

};

继续看

static struct s3c2410fb_display mini2440_lcd_cfg __initdata = {

#if !defined (LCD_CON5)

       .lcdcon5 = S3C2410_LCDCON5_FRM565 |

                       S3C2410_LCDCON5_INVVLINE |

                       S3C2410_LCDCON5_INVVFRAME |

                       S3C2410_LCDCON5_PWREN |

                       S3C2410_LCDCON5_HWSWP,

#else

       .lcdcon5 = LCD_CON5,

#endif

       .type              = S3C2410_LCDCON1_TFT,   //屏的类型

       .width            = LCD_WIDTH,        //屏宽

       .height           = LCD_HEIGHT,      //屏高

       .pixclock       = LCD_PIXCLOCK,   //时钟

       .xres              = LCD_WIDTH,        //水平分辨率

       .yres              = LCD_HEIGHT,       //垂直分辨率

       .bpp              = 16,                 //每个像素的比特数

       .left_margin    = LCD_LEFT_MARGIN + 1,       //左边界

       .right_margin  = LCD_RIGHT_MARGIN + 1,  //右边界

       .hsync_len     = LCD_HSYNC_LEN + 1,      //行同步

       .upper_margin      = LCD_UPPER_MARGIN + 1,   //上边界

       .lower_margin       = LCD_LOWER_MARGIN + 1,  //下边界

       .vsync_len     = LCD_VSYNC_LEN + 1,          //帧同步

};

好了，这样我们就完成了LCD驱动的移植工作，接着我们通过make menuconfig选择相应的文件层、设备层和X35LCD屏这个三个选项，最后编译生成内核。

 

三．LCD文件层和驱动层设计思路

LCD驱动可以分为文件层和设备层，文件层又叫FrameBuffer设备驱动，对应的文件是fbmem.c，主要实现为用户提供file_operations接口，同时为设备层提供一些函数接口，这个帧缓冲设备驱动内核已经帮我们编写好，我们不需要编写。在设备层我们专门Mini2440的LCD编写的驱动在s3c2410fb.c中，该驱动叫LCD驱动，主要是填充一个fbinfo结构，然后用register_framebuffer注册到内核，对于fbinfo结构，最主要的是填充它的fs_ops成员。对于驱动工程师，第一件事就是学会根据LCD说明文档，移植LCD。第二件事就是会写设备层LCD驱动。

3.1 LCD驱动中几个重要的数据结构

在分析内核LCD驱动代码之前，我们先要熟悉几个结构体。

struct fb_info {

       int node;

       int flags;

       struct mutex lock;

       struct mutex mm_lock;       

       struct fb_var_screeninfo var;           //当前缓冲区的可变参数

       struct fb_fix_screeninfo fix;       //当前缓冲区的固定参数

       struct fb_monspecs monspecs;

       struct work_struct queue;

       struct fb_pixmap pixmap;   

       struct fb_pixmap sprite;      

       struct fb_cmap cmap;                    //当前的调试板

       struct list_head modelist;     

       struct fb_videomode *mode;     

#ifdef CONFIG_FB_BACKLIGHT       //背光

       struct backlight_device *bl_dev;

       struct mutex bl_curve_mutex;        //背光灯层次

       u8 bl_curve[FB_BACKLIGHT_LEVELS];  //调整背光灯

#endif

#ifdef CONFIG_FB_DEFERRED_IO

       struct delayed_work deferred_work;

       struct fb_deferred_io *fbdefio;

#endif

       struct fb_ops *fbops;   //帧缓冲操作函数集合

       struct device *device;        

       struct device *dev;             

       int class_flag;                  

#ifdef CONFIG_FB_TILEBLITTING

       struct fb_tile_ops *tileops;  

#endif

       char __iomem *screen_base;     //虚拟基地址

       unsigned long screen_size;    //虚拟内存大小

       void *pseudo_palette;        

#define FBINFO_STATE_RUNNING    0

#define FBINFO_STATE_SUSPENDED      1

       u32 state;            

       void *fbcon_par;              

       void *par;            //私有数据

       resource_size_t aperture_base;

       resource_size_t aperture_size;

};

为了清晰起见，对于fb_info结构体，我只注释了重点几个成员，每个帧设备都有一个fb_info，该结构体包含了驱动实现的底层函数和记录设备状态的数据。fb_info结构体主要包含fb_var_screeninfo、fb_fix_screeninfo、fb_cmap和fb_ops，

struct fb_var_screeninfo {

       __u32 xres;                 //水平分辨率

       __u32 yres;        //垂直分辨率

       __u32 xres_virtual;            

       __u32 yres_virtual;

       __u32 xoffset;                   

       __u32 yoffset;            

       __u32 bits_per_pixel;         //每个像素所占的比特数

       __u32 grayscale;        

       struct fb_bitfield red;          

       struct fb_bitfield green;

       struct fb_bitfield blue;

       struct fb_bitfield transp;

       __u32 nonstd;            

       __u32 activate;                  

       __u32 height;               //屏高

       __u32 width;               //屏宽

       __u32 accel_flags;             

       __u32 pixclock;                  //像素时钟

       __u32 left_margin;              //左边界

       __u32 right_margin;            //右边界

       __u32 upper_margin;          //上边界

       __u32 lower_margin;   //下边界

       __u32 hsync_len;         //水平同步长度

       __u32 vsync_len;         //垂直同步长度

       __u32 sync;                

       __u32 vmode;            

       __u32 rotate;              

       __u32 reserved[5];            

};

上面的fb_var_screeninfo结构体存放了用户可以修改的显示控制器参数，如分辨率，BPP等参数。

struct fb_fix_screeninfo {

       char id[16];                

       unsigned long smem_start;   //fb缓冲区开始的位置

       __u32 smem_len;               //fb缓冲区长度

       __u32 type;         

       __u32 type_aux;         

       __u32 visual;                 //屏幕色彩模式

       __u16 xpanstep;                

       __u16 ypanstep;         

       __u16 ywrapstep;       

       __u32 line_length;       

       unsigned long mmio_start;     //内存映射开始位置

       __u32 mmio_len;              //内存映射长度

       __u32 accel;               

       __u16 reserved[3];            

};

上面这个fb_fix_screeninfo主要记录了用户不能修改的固定显示控制器参数，如缓冲区物理地址、缓冲区长度、显示色彩模式、内核映射的开始位置等，这些结构体程序都需要驱动程序初始化时设置。

struct fb_cmap {

       __u32 start;          //颜色板的第一个元素入口位置

       __u32 len;            //元素长度

       __u16 *red;         //红

       __u16 *green;   //绿

       __u16 *blue;    //蓝

       __u16 *transp;     //透明分量值     

};

对于上面的fb_cmap，它主要记录了一个颜色板信息，用户空间可以使用ioctl函数的FBIOGETCMAP和FBIOPUTCMAP读取和设置颜色表的值。

struct fb_ops {

       struct module *owner;

       int (*fb_open)(struct fb_info *info, int user);

       int (*fb_release)(struct fb_info *info, int user);

       ssize_t (*fb_read)(struct fb_info *info, char __user *buf,

                        size_t count, loff_t *ppos);

       ssize_t (*fb_write)(struct fb_info *info, const char __user *buf,

                         size_t count, loff_t *ppos);

       int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);

       int (*fb_set_par)(struct fb_info *info);

       int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,

                         unsigned blue, unsigned transp, struct fb_info *info);

       int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);

       int (*fb_blank)(int blank, struct fb_info *info);

       int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);

       void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);

       void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);

       void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);

       int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);

       void (*fb_rotate)(struct fb_info *info, int angle);

       int (*fb_sync)(struct fb_info *info);

       int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,

                     unsigned long arg);

       int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,

                     unsigned long arg);

       int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);

       void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,

                         struct fb_var_screeninfo *var);

       void (*fb_destroy)(struct fb_info *info);

};

其中fb_ops就是用来实现对帧缓冲设备的操作。

 

3.2  LCD驱动层

好了，我们先看看驱动层代码s3c2410fb.c

static struct platform_driver s3c2410fb_driver = {

       .probe           = s3c2410fb_probe,  //探测

       .remove         = s3c2410fb_remove, //移除

       .suspend = s3c2410fb_suspend,   //挂起

       .resume         = s3c2410fb_resume,  //恢复

       .driver           = {

              .name     = "s3c2410-lcd",   //驱动名

              .owner    = THIS_MODULE,

       },

};

我们看看探测函数s3c2410fb_probe

static int __init s3c2410fb_probe(struct platform_device *pdev)

{

       return s3c24xxfb_probe(pdev, DRV_S3C2410);

}

继续看

static int __init s3c24xxfb_probe(struct platform_device *pdev,

                              enum s3c_drv_type drv_type)

{

       struct s3c2410fb_info *info;  //该驱动的全局变量结构体

       struct s3c2410fb_display *display; //LCD屏的配置信息

       struct fb_info *fbinfo;    //帧缓冲驱动中对应的fb_info结构体

       struct s3c2410fb_mach_info *mach_info;  //内核平台设备数据

       struct resource *res;             //LCD资源

       int ret;

       int irq;

       int i;

       int size;

       u32 lcdcon1;

       mach_info = pdev->dev.platform_data;        //获得平台设备数据

       if (mach_info == NULL) {

              dev_err(&pdev->dev,

                     "no platform data for lcd, cannot attach\n");

              return -EINVAL;

       }

       if (mach_info->default_display >= mach_info->num_displays) {

              dev_err(&pdev->dev, "default is %d but only %d displays\n",

                     mach_info->default_display, mach_info->num_displays);

              return -EINVAL;

       }

       //获得LCD配置信息结构体

       display = mach_info->displays + mach_info->default_display;

       irq = platform_get_irq(pdev, 0);       //获得中断号

       if (irq < 0) {

              dev_err(&pdev->dev, "no irq for device\n");

              return -ENOENT;

       }

   //给帧缓冲fb_info分配空间，并将struct s3c2410fb_info作为其私有数据

       fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);

       if (!fbinfo)

              return -ENOMEM;

       platform_set_drvdata(pdev, fbinfo);   //把fb_info作为平台设备的私有数据

       info = fbinfo->par; //获得fb_info的私有数据

       info->dev = &pdev->dev; 

       info->drv_type = drv_type;

       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);//获取资源

       if (res == NULL) {

              dev_err(&pdev->dev, "failed to get memory registers\n");

              ret = -ENXIO;

              goto dealloc_fb;

       }

       size = (res->end - res->start) + 1;

       info->mem = request_mem_region(res->start, size, pdev->name);  //申请内存

       if (info->mem == NULL) {

              dev_err(&pdev->dev, "failed to get memory region\n");

              ret = -ENOENT;

              goto dealloc_fb;

       }

       info->io = ioremap(res->start, size);  //物理地址转换为虚拟地址

       if (info->io == NULL) {

              dev_err(&pdev->dev, "ioremap() of registers failed\n");

              ret = -ENXIO;

              goto release_mem;

       }

       info->irq_base = info->io + ((drv_type == DRV_S3C2412) ? S3C2412_LCDINTBASE : S3C2410_LCDINTBASE);  //基地址

       dprintk("devinit\n");

       strcpy(fbinfo->fix.id, driver_name);  //驱动名

       lcdcon1 = readl(info->io + S3C2410_LCDCON1);

       writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, info->io + S3C2410_LCDCON1);  //禁止输出使能

       fbinfo->fix.type         = FB_TYPE_PACKED_PIXELS;

       fbinfo->fix.type_aux         = 0;  //LCD屏固定参数设置

       fbinfo->fix.xpanstep         = 0;

       fbinfo->fix.ypanstep         = 0;

       fbinfo->fix.ywrapstep       = 0;

       fbinfo->fix.accel        = FB_ACCEL_NONE;

       fbinfo->var.nonstd           = 0;     //LCD屏可变参数设置

       fbinfo->var.activate          = FB_ACTIVATE_NOW;

       fbinfo->var.accel_flags     = 0;

       fbinfo->var.vmode           = FB_VMODE_NONINTERLACED;

       fbinfo->fbops                  = &s3c2410fb_ops;  //操作函数集合

       fbinfo->flags             = FBINFO_FLAG_DEFAULT;

       fbinfo->pseudo_palette      = &info->pseudo_pal;

       for (i = 0; i < 256; i++)

              info->palette_buffer[i] = PALETTE_BUFF_CLEAR;//初始化调试板为空

       ret = request_irq(irq, s3c2410fb_irq, IRQF_DISABLED, pdev->name, info);

       if (ret) {

              dev_err(&pdev->dev, "cannot get irq %d - err %d\n", irq, ret);

              ret = -EBUSY;

              goto release_regs;

       }

       info->clk = clk_get(NULL, "lcd");  //获取时钟

       if (!info->clk || IS_ERR(info->clk)) {

              printk(KERN_ERR "failed to get lcd clock source\n");

              ret = -ENOENT;

              goto release_irq;

       }

       clk_enable(info->clk);   //使能时钟

       dprintk("got and enabled clock\n");

       msleep(1);

       info->clk_rate = clk_get_rate(info->clk) //设置时钟;

       for (i = 0; i < mach_info->num_displays; i++) { //获取最大需要的显存大小

              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;

       }

       //申请fb_info的显示缓冲区空间，并将其地址写入fbinfo中

       ret = s3c2410fb_map_video_memory(fbinfo);

       if (ret) {

              printk(KERN_ERR "Failed to allocate video RAM: %d\n", ret);

              ret = -ENOMEM;

              goto release_clock;

       }

       dprintk("got video memory\n");

       fbinfo->var.xres = display->xres;  //水平分辨率

       fbinfo->var.yres = display->yres;  //垂直分辨率

       fbinfo->var.bits_per_pixel = display->bpp;  //每个像素的比特数

       s3c2410fb_init_registers(fbinfo);    //初始化GPIO寄存器

      //检查fb_info->var与fbinfo支持的哪一种分辨率、色彩模式匹配

s3c2410fb_check_var(&fbinfo->var, fbinfo);

       ret = s3c2410fb_cpufreq_register(info);

       if (ret < 0) {

              dev_err(&pdev->dev, "Failed to register cpufreq\n");

              goto free_video_memory;

       }

       ret = register_framebuffer(fbinfo);//注册帧缓冲设备fb_info到系统中

       if (ret < 0) {

              printk(KERN_ERR "Failed to register framebuffer device: %d\n",

                     ret);

              goto free_cpufreq;

       }

       ret = device_create_file(&pdev->dev, &dev_attr_debug);

       if (ret) {

              printk(KERN_ERR "failed to add debug attribute\n");

       }

       printk(KERN_INFO "fb%d: %s frame buffer device\n",

              fbinfo->node, fbinfo->fix.id);

       return 0;

 free_cpufreq:

       s3c2410fb_cpufreq_deregister(info);

free_video_memory:

       s3c2410fb_unmap_video_memory(fbinfo);

release_clock:

       clk_disable(info->clk);

       clk_put(info->clk);

release_irq:

       free_irq(irq, info);

release_regs:

       iounmap(info->io);

release_mem:

       release_resource(info->mem);

       kfree(info->mem);

dealloc_fb:

       platform_set_drvdata(pdev, NULL);

       framebuffer_release(fbinfo);

       return ret;

}

上面这个探测函数中包含了几个重要的函数，如申请帧缓冲设备的显存区空间的函数s3c2410fb_map_video_memory(fbinfo)；初始化GPIO寄存器的函数s3c2410fb_init_registers(fbinfo)；检查fb_info->var与fbinfo支持的哪一种分辨率、色彩模式匹配，并据此填充var中其他参数的函数s3c2410fb_check_var(&fbinfo->var, fbinfo)，下面我们依次对这三个函数进行分析。

 

首先看s3c2410fb_map_video_memory(fbinfo)，即申请帧缓冲设备的显存区空间的函数

static int __init s3c2410fb_map_video_memory(struct fb_info *info)

{

       struct s3c2410fb_info *fbi = info->par;  //获得fb_info的私有数据

       dma_addr_t map_dma;  //保存DMA缓冲区总线地址

       unsigned map_size = PAGE_ALIGN(info->fix.smem_len);

       dprintk("map_video_memory(fbi=%p) map_size %u\n", fbi, map_size);

       //将分配的一个写合并DMA缓存区设置为LCD屏幕的虚拟地址

       info->screen_base = dma_alloc_writecombine(fbi->dev, map_size,

                                             &map_dma, GFP_KERNEL); 

       if (info->screen_base) {

              dprintk("map_video_memory: clear %p:%08x\n",

                     info->screen_base, map_size);

              memset(info->screen_base, 0x00, map_size);  //设置DMA缓存内容为空

              //将DMA缓冲区总线地址设为fb_info不可变参数中缓存的开始位置

              info->fix.smem_start = map_dma;

              dprintk("map_video_memory: dma=%08lx cpu=%p size=%08x\n",

                     info->fix.smem_start, info->screen_base, map_size);

       }

       return info->screen_base ? 0 : -ENOMEM;

}

 

接着我们看看初始化GPIO寄存器的函数s3c2410fb_init_registers(fbinfo)

static int s3c2410fb_init_registers(struct fb_info *info)

{

       struct s3c2410fb_info *fbi = info->par;  //获得fb_info的私有数据

       struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;

       unsigned long flags;

       void __iomem *regs = fbi->io;

       void __iomem *tpal;

       void __iomem *lpcsel;

       if (is_s3c2412(fbi)) {

              tpal = regs + S3C2412_TPAL;

              lpcsel = regs + S3C2412_TCONSEL;

       } else {

              tpal = regs + S3C2410_TPAL;       

              lpcsel = regs + S3C2410_LPCSEL;

       }

       local_irq_save(flags);

//把GPIO端口C和D配置成LCD模式

modify_gpio(S3C2410_GPCUP,  mach_info->gpcup,  mach_info->gpcup_mask);

modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);

modify_gpio(S3C2410_GPDUP,  mach_info->gpdup,  mach_info->gpdup_mask);

modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);

       local_irq_restore(flags);

       dprintk("LPCSEL    = 0x%08lx\n", mach_info->lpcsel);

       writel(mach_info->lpcsel, lpcsel);

       dprintk("replacing TPAL %08x\n", readl(tpal));

       writel(0x00, tpal);

       return 0;

}

最后看看检查fb_info->var与fbinfo支持的哪一种分辨率、色彩模式匹配，并据此填充var中其他参数的函数s3c2410fb_check_var(&fbinfo->var, fbinfo)

static int s3c2410fb_check_var(struct fb_var_screeninfo *var,

                            struct fb_info *info)

{

       struct s3c2410fb_info *fbi = info->par;

       struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;

       struct s3c2410fb_display *display = NULL;

       struct s3c2410fb_display *default_display = mach_info->displays +

                                              mach_info->default_display;

       int type = default_display->type; //获取LCD类型，TFT

       unsigned i;

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

       //验证x/y解析度

       if (var->yres == default_display->yres &&

           var->xres == default_display->xres &&

           var->bits_per_pixel == default_display->bpp)

              display = default_display;

       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;

                     }

       if (!display) {

              dprintk("wrong resolution or depth %dx%d at %d bpp\n",

                     var->xres, var->yres, var->bits_per_pixel);

              return -EINVAL;

       }

       var->xres_virtual = display->xres; //配置屏的虚拟解析像素

       var->yres_virtual = display->yres;

       var->height = display->height; //配置屏的高度宽度

       var->width = display->width;

       var->pixclock = display->pixclock;   //配置屏的时钟

       var->left_margin = display->left_margin; //配置屏的行帧同步、水平垂直同步

       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;  ///配置LCD寄存器

       fbi->regs.lcdcon1 = display->type;

       var->transp.offset = 0;  //配置透明度

       var->transp.length = 0;

       //根据BBP来设置可变参数RGB的颜色位域

       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;

       case 8:

              if (display->type != S3C2410_LCDCON1_TFT) {

                     var->red.length            = 3;

                     var->red.offset            = 5;

                     var->green.length  = 3;

                     var->green.offset  = 2;

                     var->blue.length    = 2;

                     var->blue.offset    = 0;

              } else {

                     var->red.offset            = 0;

                     var->red.length            = 8;

                     var->green           = var->red;

                     var->blue             = var->red;

              }

              break;

       case 12:

              var->red.length            = 4;

              var->red.offset            = 8;

              var->green.length  = 4;

              var->green.offset  = 4;

              var->blue.length    = 4;

              var->blue.offset    = 0;

              break;

       default:

       case 16:

              if (display->lcdcon5 & S3C2410_LCDCON5_FRM565) {

                     var->red.offset            = 11;  //偏移

                     var->green.offset  = 5;

                     var->blue.offset    = 0;

                     var->red.length            = 5;   //长度

                     var->green.length  = 6;

                     var->blue.length    = 5;

              } else {

                     var->red.offset            = 11;

                     var->green.offset  = 6;

                     var->blue.offset    = 1;

                     var->red.length            = 5;

                     var->green.length  = 5;

                     var->blue.length    = 5;

              }

              break;

       case 32:

              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;

}

好了，我们已经分析完LCD驱动中probe探测函数了，该函数主要是分配fb_info结构体空间，然后填充fb_info，初始化GPIO控制器，检查并设置fb_info中可变参数，申请帧缓冲设备的显示缓冲区空间，最后调用register_framebuffer函数注册到内核。

 

下面我们把重点放在fb_info结构体的fb_ops成员上

static struct fb_ops s3c2410fb_ops = {

       .owner           = THIS_MODULE,

       .fb_check_var      = s3c2410fb_check_var,  //检查参数

       .fb_set_par    = s3c2410fb_set_par,    //激活fb_info参数配置

       .fb_blank       = s3c2410fb_blank,    //显示空白

       .fb_setcolreg  = s3c2410fb_setcolreg,  //设置颜色表

       .fb_fillrect      = cfb_fillrect,        //可选

       .fb_copyarea = cfb_copyarea,        //可选

       .fb_imageblit  = cfb_imageblit,    //可选

};

fp_ops是使得帧缓冲设备工作所需函数的集合，它们最终与LCD控制器打交道。

s3c2410fb_check_va用于调整可变参数，并修改为硬件所支持的值；s3c2410fb_set_par则根据屏幕参数设置具体读写LCD控制器的寄存器，使得LCD控制器进入相应的工作状态。对于fb_ops中的.fb_fillrect、fb_copyarea和fb_imageblit，我们通常使用通用的cfb_fillrect、cfb_copyarea和cfb_imageblit函数即可。s3c2410fb_setcolreg是用来实现伪颜色表和颜色表的填充。

 

对于fb_ops中的成员中s3c2410fb_check_va这个函数在上面probe探测函数中已经讲过了，剩下的任务就是分析下激活fb_info参数配置函数s3c2410fb_set_par和显示空白函数s3c2410fb_blank。

首先看看显示空白函数s3c2410fb_blank

static int s3c2410fb_blank(int blank_mode, struct fb_info *info)

{

       struct s3c2410fb_info *fbi = info->par;   //获得fb_info私有数据

       void __iomem *tpal_reg = fbi->io;  //获得内存指针

       dprintk("blank(mode=%d, info=%p)\n", blank_mode, info);

       tpal_reg += is_s3c2412(fbi) ? S3C2412_TPAL : S3C2410_TPAL;

       //根据显示空白的模式设置LCD开启或停止

if (blank_mode == FB_BLANK_POWERDOWN) {

              s3c2410fb_lcd_enable(fbi, 0);  //停止LCD

       } else {

              s3c2410fb_lcd_enable(fbi, 1);  //开启LCD

       }

       //根据显示空白的模式控制临时调色板是否有效

       if (blank_mode == FB_BLANK_UNBLANK)

              writel(0x0, tpal_reg);         //调色板寄存器无效

       else {

              dprintk("setting TPAL to output 0x000000\n");

              writel(S3C2410_TPAL_EN, tpal_reg); //调色板寄存器有效

       }

       return 0;

}

跟踪s3c2410fb_blank中的s3c2410fb_lcd_enable函数

static void s3c2410fb_lcd_enable(struct s3c2410fb_info *fbi, int enable)

{

       unsigned long flags;

       local_irq_save(flags);

       if (enable)

              fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID; //开启LCD

       else

              fbi->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID; //关闭LCD

       writel(fbi->regs.lcdcon1, fbi->io + S3C2410_LCDCON1);

       local_irq_restore(flags);

}

 

接着看看这个根据fbinfo->var激活fb_info中的参数配置函数s3c2410fb_set_par

static int s3c2410fb_set_par(struct fb_info *info)

{

       struct fb_var_screeninfo *var = &info->var;

       switch (var->bits_per_pixel) {//根据色位模式设置色彩模式

       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;

       }

   //设置fb_info中固定参数中一行的字节数

       info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;

       s3c2410fb_activate_var(info); //激活fb_info参数配置

       return 0;

}

我们看看s3c2410fb_set_par中激活fb_info参数配置函数s3c2410fb_activate_var

static void s3c2410fb_activate_var(struct fb_info *info)

{

       struct s3c2410fb_info *fbi = info->par;

       void __iomem *regs = fbi->io;

       int type = fbi->regs.lcdcon1 & S3C2410_LCDCON1_TFT;

       struct fb_var_screeninfo *var = &info->var;

       int clkdiv;

       //计算LCD控制器1中的CLKVAL值

       clkdiv = DIV_ROUND_UP(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) { //配置TFT屏LCD控制寄存器

              s3c2410fb_calculate_tft_lcd_regs(info, &fbi->regs);

              --clkdiv;

              if (clkdiv < 0)

                     clkdiv = 0;

       } else {   //配置STN屏LCD控制寄存器

              s3c2410fb_calculate_stn_lcd_regs(info, &fbi->regs);

              if (clkdiv < 2)

                     clkdiv = 2;

       }

       //设置LCD控制器1中的CLKVAL值

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

       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);

       //设置LCD控制器1-5的参数

       writel(fbi->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID,

              regs + S3C2410_LCDCON1);

       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);

       s3c2410fb_set_lcdaddr(info); //设置帧缓冲起始地址寄存器1-3

       fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID,

       writel(fbi->regs.lcdcon1, regs + S3C2410_LCDCON1);

}

 

下面我们主要关注s3c2410fb_calculate_tft_lcd_regs和s3c2410fb_set_lcdaddr函数

static void s3c2410fb_calculate_tft_lcd_regs(const struct fb_info *info,

                                        struct s3c2410fb_hw *regs)

{

       const struct s3c2410fb_info *fbi = info->par;

       const struct fb_var_screeninfo *var = &info->var;

       switch (var->bits_per_pixel) {//根据色模式设置LCD控制器1和5

       case 1:

              regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP;

              break;

       case 2:

              regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP;

              break;

       case 4:

              regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP;

              break;

       case 8:

              regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP;

              regs->lcdcon5 |= S3C2410_LCDCON5_BSWP |

                             S3C2410_LCDCON5_FRM565;

              regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP;

              break;

       case 16:

              regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP;

              regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP;

              regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP;

              break;

       case 32:

              regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP;

              regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP |

                               S3C2410_LCDCON5_HWSWP |

                               S3C2410_LCDCON5_BPP24BL);

              break;

       default:

              dev_err(fbi->dev, "invalid bpp %d\n",

                     var->bits_per_pixel);

       }

       dprintk("setting vert: up=%d, low=%d, sync=%d\n",

              var->upper_margin, var->lower_margin, var->vsync_len);

       dprintk("setting horz: lft=%d, rt=%d, sync=%d\n",

              var->left_margin, var->right_margin, var->hsync_len);

       //设置LCD控制器2、3、4

       regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) |

                     S3C2410_LCDCON2_VBPD(var->upper_margin - 1) |

                     S3C2410_LCDCON2_VFPD(var->lower_margin - 1) |

                     S3C2410_LCDCON2_VSPW(var->vsync_len - 1);

       regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) |

                     S3C2410_LCDCON3_HFPD(var->left_margin - 1) |

                     S3C2410_LCDCON3_HOZVAL(var->xres - 1);

       regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1);

}

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;

       saddr1  = info->fix.smem_start >> 1;

       saddr2  = info->fix.smem_start;

       saddr2 += info->fix.line_length * info->var.yres;

       saddr2 >>= 1;

       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);

       //初始化LCD控制器的地址指针

       writel(saddr1, regs + S3C2410_LCDSADDR1);

       writel(saddr2, regs + S3C2410_LCDSADDR2);

       writel(saddr3, regs + S3C2410_LCDSADDR3);

}

归纳下我们分析的这个激活fb_info参数配置函数s3c2410fb_activate_var，该函数主要是计算clkval的值，计算LCD控制器1-5的值，然后设置LCD控制器1-5，并设置帧缓冲寄存器。