Linux LCD驱动分析

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。

drivers/video/s3c2410fb.c
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);//s3c_device_lcd->dev.platform_data = 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。

以上这些是我们port一个LCD驱动时候必须完成的工作

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.cstatic 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_val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)

{
/*下面的 saddr1 saddr2 saddr3 三个addr为啥要这样设置，请大神指教**/
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);

}