lcd设备驱动之全解析.docx

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1、linux中LCD设备驱动（1）framebuffer(帧缓冲)1、framebuffer 帧缓冲 帧缓冲（framebuffer）是Linux 系统为显示设备提供的一个接口，它将显示缓冲区抽象，屏蔽图像硬件的底层差异，允许上层应用程序在图形模式下直接对显示缓冲区进行读写操作。用户不必关心物理显示缓冲区的具体位置及存放方式，这些都由帧缓冲设备驱动本身来完成。 framebuffer机制模仿显卡的功能，将显卡硬件结构抽象为一系列的数据结构，可以通过framebuffer的读写直接对显存进行操作。用户可以将framebuffer看成是显存的一个映像，将其映射到进程空间后，就可以直接进行读写操作，写

2、操作会直接反映在屏幕上。 framebuffer是个字符设备，主设备号为29，对应于/dev/fb%d 设备文件。通常，使用如下方式（前面的数字表示次设备号） 0 = /dev/fb0 第一个fb 设备 1 = /dev/fb1 第二个fb 设备 fb 也是一种普通的内存设备，可以读写其内容。例如，屏幕抓屏：cp /dev/fb0 myfilefb 虽然可以像内存设备（/dev/mem）一样，对其read,write,seek 以及mmap。但区别在于fb 使用的不是整个内存区，而是显存部分。2、fb与应用程序的交互对于用户程序而言，它和其他的设备并没有什么区别，用户可以把fb看成是一块内存，

3、既可以向内存中写数据，也可以读数据。fb的显示缓冲区位于内核空间，应用程序可以把此空间映射到自己的用户空间，在进行操作。在应用程序中，操作/dev/fbn的一般步骤如下：（1）打开/dev/fbn设备文件。（2）用ioctl()操作取得当前显示屏幕的参数，如屏幕分辨率、每个像素点的比特数。根据屏幕参数可计算屏幕缓冲区的大小。（3）用mmap()函数，将屏幕缓冲区映射到用户空间。（4）映射后就可以直接读/写屏幕缓冲区，进行绘图和图片显示了。3、fb的结构及其相关结构体在linux中，fb设备驱动的源码主要在Fb.h (linux2.6.28includelinux)和Fbmem.c (linux

4、2.6.28driversvideo)两个文件中，它们是fb设备驱动的中间层，为上层提供系统调用，为底层驱动提供接口。在fb.h文件中有fb驱动需要使用的很多结构，我们先对这些结构体进行说明：本章共介绍5个结构体：(1)、struct fb_info结构体(2)、struct fb_ops结构体(3)、struct fb_fix_screeninfo结构体(4)、struct fb_var_screeninfo结构体(5)、struct fb_cmap结构体（1）、struct fb_info结构体介绍一个帧缓冲区对应一个struct fb_info结构，它包括了帧缓冲设备的属性和操作的完整集

5、合，每个帧设备都有一个fb_info结构体。源码如下：struct fb_info int node;int flags;struct mutex lock;/* Lock for open/release/ioctl funcs */互斥锁struct fb_var_screeninfo var;/* Current var */当前缓冲区的可变参数struct fb_fix_screeninfo fix;/* Current fix */固定参数struct fb_monspecs monspecs;/* Current Monitor specs */当前显示器标志struct work

6、_struct queue;/* Framebuffer event queue */帧缓冲事件队列struct fb_pixmap pixmap;/* Image hardware mapper */图像硬件mapperstruct fb_pixmap sprite;/* Cursor hardware mapper */光标硬件mapperstruct fb_cmap cmap;/* Current cmap */当前的调色板struct list_head modelist; /* mode list */struct fb_videomode *mode;/* current mode

7、 */当前的视频模式#ifdef CONFIG_FB_BACKLIGHT如果配置了LCD支持背光灯/* assigned backlight device */* set before framebuffer registration, remove after unregister */背光调整struct backlight_device *bl_dev;/* Backlight level curve */struct mutex bl_curve_mutex;u8 bl_curveFB_BACKLIGHT_LEVELS;#endif#ifdef CONFIG_FB_DEFERRED_I

8、Ostruct delayed_work deferred_work;struct fb_deferred_io *fbdefio;#endifstruct fb_ops *fbops;帧缓冲操作函数集struct device *device;/* This is the parent */父设备struct device *dev;/* This is this fb device */fb设备int class_flag; /* private sysfs flags */私有的sysfs标志#ifdef CONFIG_FB_TILEBLITTINGstruct fb_tile_ops

9、*tileops; /* Tile Blitting */图块blitting#endifchar _iomem *screen_base;/* Virtual address */虚拟基地址unsigned long screen_size;/* Amount of ioremapped VRAM or 0 */ ioremap的虚拟内存大小void *pseudo_palette;/* Fake palette of 16 colors */ 伪16位调色板#define FBINFO_STATE_RUNNING 0#define FBINFO_STATE_SUSPENDED 1u32 s

10、tate; /* Hardware state i.e suspend */硬件的状态void *fbcon_par; /* fbcon use-only private area */* From here on everything is device dependent */void *par; ;（2）、struct fb_ops结构体介绍/*Frame buffer operations* LOCKING NOTE: those functions must _ALL_ be called with the console* semaphore held, this is the o

11、nly suitable locking mechanism we have* in 2.6. Some may be called at interrupt time at this point though.*/fb_ops结构体用来实现对帧缓冲设备的操作，这些函数需要驱动开发人员编写，struct fb_ops /* open/release and usage marking */struct module *owner;打开和释放int (*fb_open)(struct fb_info *info, int user);int (*fb_release)(struct fb_inf

12、o *info, int user);这两个函数对于非线性布局的/常规内存映射无法工作的帧缓冲设备需要/* For framebuffers with strange non linear layouts or that do not* work with normal memory mapped access*/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 _us

13、er *buf, size_t count, loff_t *ppos);检测可变参数，并调整到支持的值/* checks var and eventually tweaks it to something supported,* DO NOT MODIFY PAR */int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);设置视频模式/* set the video mode according to info-var */int (*fb_set_par)(struct fb_info *info)

14、;设置color寄存器的值/* set color register */int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green, unsigned blue, unsigned transp, struct fb_info *info);批量设置color寄存器，设置颜色表/* set color registers in batch */int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);显示空白/* blank display */int (*

15、fb_blank)(int blank, struct fb_info *info);pan显示/* pan display */int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);填充矩形/* Draws a rectangle */void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);数据复制/* Copy data from area to another */void (*fb_copyarea

16、) (struct fb_info *info, const struct fb_copyarea *region);图形填充/* Draws a image to the display */void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);绘制光标/* Draws cursor */int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);旋转显示/* Rotates the display */void (*fb_ro

17、tate)(struct fb_info *info, int angle);等待blit空闲/* wait for blit idle, optional */int (*fb_sync)(struct fb_info *info);fb特定的ioctl操作/* perform fb specific ioctl (optional) */int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,unsigned long arg);处理32兼容的ioctl操作/* Handle 32bit compat ioctl (optional)

18、*/int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,unsigned long arg);fb特定的mmap操作/* perform fb specific mmap */int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);保存目前的硬件状态/* save current hardware state */void (*fb_save_state)(struct fb_info *info);恢复被保存的硬件状态/* restore saved st

19、ate */void (*fb_restore_state)(struct fb_info *info);通过fb_info获得framebuffer的能力/* get capability given var */void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps, struct fb_var_screeninfo *var);（3）、struct fb_fix_screeninfo结构体接收fb_fix_screeninfo结构体中，记录了用户不能修改的固定显示控制器参数。这些固定的参数如缓冲区的物理地址、

20、缓冲区的长度等等。struct fb_fix_screeninfo char id16; /* identification string eg TT Builtin */字符串形式的标识符unsigned long smem_start;/* Start of frame buffer mem */* (physical address) */fb缓存的开始位置_u32 smem_len;/* Length of frame buffer mem */fb缓存的长度_u32 type; /* see FB_TYPE_* */FB_TYPE_*类型_u32 type_aux;/* Interl

21、eave for interleaved Planes */分界_u32 visual; /* see FB_VISUAL_* */屏幕使用的色彩模式_u16 xpanstep;/* zero if no hardware panning */如果没有硬件panning ，赋0_u16 ypanstep;/* zero if no hardware panning */_u16 ywrapstep;/* zero if no hardware ywrap */1行的字节数_u32 line_length;/* length of a line in bytes */内存映射I/O的开始位置un

22、signed long mmio_start;/* Start of Memory Mapped I/O */* (physical address) */内存映射I/O的长度_u32 mmio_len;/* Length of Memory Mapped I/O */_u32 accel; /* Indicate to driver which */* specific chip/card we have*/_u16 reserved3;/* Reserved for future compatibility */;（4）、struct fb_var_screeninfo结构体介绍fb_va

23、r_screeninfo结构体中存储了用户可以修改的显示器控制参数，例如屏幕分辨率、透明度等等。struct fb_var_screeninfo _u32 xres; /* visible resolution */_u32 yres;可见解析度，即分辨率_u32 xres_virtual;/* virtual resolution*/_u32 yres_virtual;虚拟解析度_u32 xoffset;/* offset from virtual to visible */_u32 yoffset;/* resolution*/虚拟到可见之间的偏移_u32 bits_per_pixel;/

24、* guess what*/每像素位数，BPP_u32 grayscale;/* != 0 Graylevels instead of colors */非0时指灰度struct fb_bitfield red;/* bitfield in fb mem if true color, */struct fb_bitfield green;/* else only length is significant */struct fb_bitfield blue;fb缓存的RGB位域struct fb_bitfield transp;/* transparency*/透明度_u32 nonstd;

25、/* != 0 Non standard pixel format */!= 0 非标准像素格式_u32 activate;/* see FB_ACTIVATE_*/ _u32 height; /* height of picture in mm */屏幕的高度_u32 width; /* width of picture in mm */屏幕的宽度_u32 accel_flags;/* (OBSOLETE) see fb_info.flags */fb_info的标志/* Timing: All values in pixclocks, except pixclock (of course)

26、 */_u32 pixclock;/* pixel clock in ps (pico seconds) */* 像素时钟（皮秒） */_u32 left_margin;/* time from sync to picture*/行切换：从同步到绘图之间的延迟_u32 right_margin;/* time from picture to sync*/ 行切换：从绘图到同步之间的延迟_u32 upper_margin;/* time from sync to picture*/ 帧切换：从同步到绘图之间的延迟_u32 lower_margin; 帧切换：从绘图到同步之间的延迟_u32 hsy

27、nc_len;/* length of horizontal sync*/ 水平同步的长度_u32 vsync_len;/* length of vertical sync*/ 垂直同步的长度_u32 sync; /* see FB_SYNC_* */_u32 vmode; /* see FB_VMODE_* */_u32 rotate; /* angle we rotate counter clockwise */ 顺时钟旋转的角度_u32 reserved5;/* Reserved for future compatibility */;（5）、struct fb_cmap结构体介绍fb_

28、cmap结构体中记录了颜色板信息，即调色板信息。，用户空间可以通过ioctl()的FBIOGETCMAP和 FBIOPUTCMAP命令读取或设定颜色表。struct fb_cmap _u32 start; /* First entry */第一个元素的入口_u32 len; /* Number of entries */元素个数_u16 *red; /* Red values */红色、绿色、蓝色_u16 *green; _u16 *blue;_u16 *transp;/* transparency, can be NULL */透明度;上面这些结构体之间有什么关系呢？看下图：（6）、fb_b

29、itfield 结构体描述每一像素显示缓冲区的组织方式，包含位域偏移、位域长度和MSB 指示，struct fb_bitfield _u32 offset; /* beginning of bitfield */ 位域偏移_u32 length; /* length of bitfield */ 位域长度_u32 msb_right;/* != 0 : Most significant bit is */* right */ MSB;上一篇说了framebuffer帧缓冲的有关知识，这一篇具体的说下LCD驱动的实现。1、LCD设备驱动在linux内核中是作为平台设备存在，所以又要说那些已经说过

30、很多遍的东西。int _devinit s3cfb_init(void)return platform_driver_register(&s3cfb_driver);static void _exit s3cfb_cleanup(void)platform_driver_unregister(&s3cfb_driver);module_init(s3cfb_init);module_exit(s3cfb_cleanup);对应的platform_driver结构体为：static struct platform_driver s3cfb_driver = .probe = s3cfb_prob

31、e,.remove = s3cfb_remove,.suspend = s3cfb_suspend,.resume = s3cfb_resume, .driver = .name = s3c-lcd,.owner = THIS_MODULE,;那么平台设备的资源呢？/* LCD Controller */static u64 s3c_device_lcd_dmamask = 0xffffffffUL;struct platform_device s3c_device_lcd = .name = s3c-lcd,.id = -1,设备编号，-1表示只有这样一个设备.num_resources=

32、ARRAY_SIZE(s3c_lcd_resource),.resource = s3c_lcd_resource,.dev = .dma_mask = &s3c_device_lcd_dmamask,.coherent_dma_mask= 0xffffffffUL;static struct resource s3c_lcd_resource = 0 = .start = S3C64XX_PA_LCD, /LCD的I/O内存的开始位置.end = S3C64XX_PA_LCD + SZ_1M - 1,.flags = IORESOURCE_MEM,1 = .start = IRQ_LCD_V

33、SYNC, /LCD的开始中断号.end = IRQ_LCD_SYSTEM, /LCD的结束中断号.flags = IORESOURCE_IRQ,;2、分析其probe函数，源码如下：/* Probe*/static int _init s3cfb_probe(struct platform_device *pdev)struct resource *res;struct fb_info *fbinfo;s3cfb_info_t *info;char driver_name = s3cfb;int index = 0, ret, size;fbinfo = framebuffer_alloc(

34、sizeof(s3cfb_info_t), &pdev-dev);申请一个s3cfb_info_t结构体的空间if (!fbinfo)return -ENOMEM;platform_set_drvdata(pdev, fbinfo);info = fbinfo-par;info-dev = &pdev-dev; 填充info结构体变量的相应信息res = platform_get_resource(pdev, IORESOURCE_MEM, 0)；获取LCD平台设备所使用的I/O端口资源。if (res = NULL) dev_err(&pdev-dev, failed to get memo

35、ry registersn);ret = -ENXIO;goto dealloc_fb;size = (res-end - res-start) + 1;info-mem = request_mem_region(res-start, size, pdev-name);申请LCD设备所占的I/O空间if (info-mem = NULL) dev_err(&pdev-dev, failed to get memory regionn);ret = -ENOENT;goto dealloc_fb;info-io = ioremap(res-start, size);将LCD的I/O端口所占用的这

36、段I/O空间映射到内存的虚拟地址。if (info-io = NULL) dev_err(&pdev-dev, ioremap() of registers failedn);ret = -ENXIO;goto release_mem;s3cfb_pre_init();这个函数的源码在S3cfb_fimd4x.c (linux2.6.28driversvideosamsung)文件中，如下所示：void s3cfb_pre_init(void)/* initialize the fimd specific */s3cfb_fimd.vidintcon0 &= S3C_VIDINTCON0_FR

37、AMESEL0_MASK;s3cfb_fimd.vidintcon0 |= S3C_VIDINTCON0_FRAMESEL0_VSYNC;s3cfb_fimd.vidintcon0 |= S3C_VIDINTCON0_INTFRMEN_ENABLE;writel(s3cfb_fimd.vidintcon0, S3C_VIDINTCON0);这个函数中涉及到一个结构体s3cfb_fimd_info_t s3cfb_fimd，和这个函数在同一个文件中定义，列出部分源码：s3cfb_fimd_info_t s3cfb_fimd = .vidcon0 = S3C_VIDCON0_INTERLACE_F

38、_PROGRESSIVE | S3C_VIDCON0_VIDOUT_RGB_IF | S3C_VIDCON0_L1_DATA16_SUB_16_MODE | S3C_VIDCON0_L0_DATA16_MAIN_16_MODE | S3C_VIDCON0_PNRMODE_RGB_P | S3C_VIDCON0_CLKVALUP_ALWAYS | S3C_VIDCON0_CLKDIR_DIVIDED | S3C_VIDCON0_CLKSEL_F_HCLK | S3C_VIDCON0_ENVID_DISABLE | S3C_VIDCON0_ENVID_F_DISABLE,.dithmode = (

39、S3C_DITHMODE_RDITHPOS_5BIT | S3C_DITHMODE_GDITHPOS_6BIT | S3C_DITHMODE_BDITHPOS_5BIT ) & S3C_DITHMODE_DITHERING_DISABLE,#if defined (CONFIG_FB_S3C_BPP_8).wincon0 = S3C_WINCONx_BYTSWP_ENABLE | S3C_WINCONx_BURSTLEN_4WORD | S3C_WINCONx_BPPMODE_F_8BPP_PAL,.wincon1 = S3C_WINCONx_HAWSWP_ENABLE | S3C_WINCO

40、Nx_BURSTLEN_4WORD | S3C_WINCONx_BPPMODE_F_16BPP_565 | S3C_WINCONx_BLD_PIX_PLANE | S3C_WINCONx_ALPHA_SEL_1,.bpp = S3CFB_PIXEL_BPP_8,.bytes_per_pixel = 1,.wpalcon = S3C_WPALCON_W0PAL_16BIT,.vidosd1c = S3C_VIDOSDxC_ALPHA1_B(S3CFB_MAX_ALPHA_LEVEL) | S3C_VIDOSDxC_ALPHA1_G(S3CFB_MAX_ALPHA_LEVEL) | S3C_VID

41、OSDxC_ALPHA1_R(S3CFB_MAX_ALPHA_LEVEL),.vidosd2c = S3C_VIDOSDxC_ALPHA1_B(S3CFB_MAX_ALPHA_LEVEL) | S3C_VIDOSDxC_ALPHA1_G(S3CFB_MAX_ALPHA_LEVEL) | S3C_VIDOSDxC_ALPHA1_R(S3CFB_MAX_ALPHA_LEVEL),.vidosd3c = S3C_VIDOSDxC_ALPHA1_B(S3CFB_MAX_ALPHA_LEVEL) | S3C_VIDOSDxC_ALPHA1_G(S3CFB_MAX_ALPHA_LEVEL) | S3C_V

42、IDOSDxC_ALPHA1_R(S3CFB_MAX_ALPHA_LEVEL),.vidosd4c = S3C_VIDOSDxC_ALPHA1_B(S3CFB_MAX_ALPHA_LEVEL) | S3C_VIDOSDxC_ALPHA1_G(S3CFB_MAX_ALPHA_LEVEL) | S3C_VIDOSDxC_ALPHA1_R(S3CFB_MAX_ALPHA_LEVEL),.vidintcon0 = S3C_VIDINTCON0_FRAMESEL0_VSYNC | S3C_VIDINTCON0_FRAMESEL1_NONE | S3C_VIDINTCON0_INTFRMEN_DISABL

43、E | S3C_VIDINTCON0_FIFOSEL_WIN0 | S3C_VIDINTCON0_FIFOLEVEL_25 | S3C_VIDINTCON0_INTFIFOEN_DISABLE | S3C_VIDINTCON0_INTEN_ENABLE,.vidintcon1 = 0,.xoffset = 0,.yoffset = 0,.w1keycon0 = S3C_WxKEYCON0_KEYBLEN_DISABLE | S3C_WxKEYCON0_KEYEN_F_DISABLE | S3C_WxKEYCON0_DIRCON_MATCH_FG_IMAGE | S3C_WxKEYCON0_CO

44、MPKEY(0x0),.w4keycon1 = S3C_WxKEYCON1_COLVAL(0xffffff),.sync = 0,.cmap_static = 1,.vs_offset = S3CFB_DEFAULT_DISPLAY_OFFSET,.brightness = S3CFB_DEFAULT_BRIGHTNESS,.backlight_level = S3CFB_DEFAULT_BACKLIGHT_LEVEL,.backlight_power = 1,.lcd_power = 1,;那么对应的结构体原型在哪呢？在S3cfb.h (linux2.6.28driversvideosams

45、ung)文件中，如下所示：看那些对应的注释，也应该大致明白这个结构体的作用，存储与显示控制器有关的信息，还有显示屏幕的信息。不知道大家对s3cfb_fimd_info_t这个结构体的命名有何看法？名字往往代表了这个结构体的作用。其实这个结构体的名字给我们的信息是：fimd FIMD:Fully Interactive Mobile Display （完全交互式移动显示设备）这是第一个概念，另一个概念是OSD，我查了下资料，有这样的含义：OSD是on-screen display的简称，即屏幕菜单式调节方式。一般是按Menu键后屏幕弹出的显示器各项调节项目信息的矩形菜单，可通过该菜单对显示器各项工作指标包括色彩、模式、几何形状等进行调整，从而达到最佳的使用状态。现在对这个结构体的认识是不是深刻多了？typedef struct /* Screen size *