总算要涉及到LCD的驱动程序了，不过之前还是先弄一下LCD的测试程序的好（这里看的是国嵌的代码）！

之前在电脑上找了很久的LCD的驱动程序，也就是xxxfb.c，但是真心看不懂究竟是哪个驱动，但是共性的文件fbmem.c还是可以了解的，这里就通过fbmem.c来进行简单的介绍吧，至于涉及到的相关的硬件设备（今天写的驱动测试没有涉及到硬件的具体信息），只能等以后再说了！

LCD 驱动测试程序：

首先介绍一下 Framebuffer：Framebuffer 从本质上讲是图形设备的硬件抽象。对开发者而言， Framebuffer 是一块显示缓存，往缓存中写入特定格式的数据就意味着向屏幕输出内容。通过不断的向 Framebuffer 中写入数据，显示控制器就会自动的从 Framebuffer 中取数据并显示出来，帧缓冲设备对应的设备文件为 /dev/fb0，如果系统有多个显示卡， Linux 下还可以支持多个帧缓冲设备，通常指向 /dev/fb0。真缓冲设备为标准的字符设备，主设备号为 29，次设备号从 0 到 31。

 

下面可以看看帧缓冲设备的架构：

 

 

1、帧缓冲设备结构体介绍：

 

Linux 内核使用 fb_info 结构来描述帧缓冲设备，定义在 include/linux/fb.h 中， fb_infor 结构常用成员：

 

struct fb_info {
	int node;
	int flags;
	struct mutex lock;		/* Lock for open/release/ioctl funcs */
	struct mutex mm_lock;		/* Lock for fb_mmap and smem_* fields */
	struct fb_var_screeninfo var;	/* Current var */
	struct fb_fix_screeninfo fix;	/* Current fix */
	struct fb_monspecs monspecs;	/* Current Monitor specs */
	struct work_struct queue;	/* Framebuffer event queue */
	struct fb_pixmap pixmap;	/* Image hardware mapper */
	struct fb_pixmap sprite;	/* Cursor hardware mapper */
	struct fb_cmap cmap;		/* Current cmap */
	struct list_head modelist;      /* mode list */
	struct fb_videomode *mode;	/* current mode */

	/* we need the PCI or similiar aperture base/size not
	   smem_start/size as smem_start may just be an object
	   allocated inside the aperture so may not actually overlap */
	struct apertures_struct {
		unsigned int count;
		struct aperture {
			resource_size_t base;
			resource_size_t size;
		} ranges[0];
	} *apertures;
};

 

其中 fb_var_screeninfo 结构记录了用户可以修改的显示参数，包括屏幕分辨率等。 

struct fb_var_screeninfo {
	__u32 xres;			/* visible resolution		*/
	__u32 yres;
	__u32 xres_virtual;		/* virtual resolution		*/
	__u32 yres_virtual;
	__u32 xoffset;			/* offset from virtual to visible */
	__u32 yoffset;			/* resolution			*/

	__u32 bits_per_pixel;		/* guess what			*/
	__u32 grayscale;		/* != 0 Graylevels instead of colors */

	struct fb_bitfield red;		/* bitfield in fb mem if true color, */
	struct fb_bitfield green;	/* else only length is significant */
	struct fb_bitfield blue;
	struct fb_bitfield transp;	/* transparency			*/	

	__u32 nonstd;			/* != 0 Non standard pixel format */

	__u32 activate;			/* see FB_ACTIVATE_*		*/

	__u32 height;			/* height of picture in mm    */
	__u32 width;			/* width of picture in mm     */

	__u32 accel_flags;		/* (OBSOLETE) see fb_info.flags */

};

 

fb_fix_screeninfo 记录了用户不能修改的显示控制器参数，如显示缓存的物理地址等。

struct fb_fix_screeninfo {
	char id[16];			/* identification string eg "TT Builtin" */
	unsigned long smem_start;	/* Start of frame buffer mem */
					/* (physical address) */
	__u32 smem_len;			/* Length of frame buffer mem */
	__u32 type;			/* see FB_TYPE_*		*/
	__u32 type_aux;			/* Interleave for interleaved Planes */
	__u32 visual;			/* see FB_VISUAL_*		*/ 
	__u16 xpanstep;			/* zero if no hardware panning  */
	__u16 ypanstep;			/* zero if no hardware panning  */
	__u16 ywrapstep;		/* zero if no hardware ywrap    */
	__u32 line_length;		/* length of a line in bytes    */
	unsigned long mmio_start;	/* Start of Memory Mapped I/O   */
					/* (physical address) */
	__u32 mmio_len;			/* Length of Memory Mapped I/O  */
	__u32 accel;			/* Indicate to driver which	*/
					/*  specific chip/card we have	*/
	__u16 reserved[3];		/* Reserved for future compatibility */
};

 

还有就是 fb_ops 结构包含了对控制器进行操作的函数指针。

struct fb_ops {
	/* open/release and usage marking */
	struct module *owner;
	int (*fb_open)(struct fb_info *info, int user);
	int (*fb_release)(struct fb_info *info, int user);

	/* 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 __user *buf,
			    size_t count, loff_t *ppos);

	/* 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);

	/* set the video mode according to info->var */
	int (*fb_set_par)(struct fb_info *info);

	/* set color register */
	int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,
			    unsigned blue, unsigned transp, struct fb_info *info);

	/* set color registers in batch */
	int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);

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

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

	/* Draws a rectangle */
	void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);
	/* Copy data from area to another */
	void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);
	/* Draws a image to the display */
	void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);

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

	/* Rotates the display */
	void (*fb_rotate)(struct fb_info *info, int angle);

	/* wait for blit idle, optional */
	int (*fb_sync)(struct fb_info *info);

};

 

2、控制器操作函数（fbmem.c）：

 

这里首先讲述一下 LCD 测试程序的基本步骤：

 1）用 ioctl 操作取得当前屏幕的参数，根据屏幕参数可以计算屏幕缓冲区的大小。

2）将屏幕缓冲区映射到用户空间（mmap）。

3）映射后即可直接读写

 

这里用到 open、release、ioctl 等函数，主要介绍下 ioctl 函数吧，代码如下：

 

static long fb_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct inode *inode = file->f_path.dentry->d_inode;
	int fbidx = iminor(inode);
	struct fb_info *info = registered_fb[fbidx];

	return do_fb_ioctl(info, cmd, arg);
}

static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
			unsigned long arg)
{
	struct fb_ops *fb;
	struct fb_var_screeninfo var;
	struct fb_fix_screeninfo fix;
	struct fb_con2fbmap con2fb;
	struct fb_cmap cmap_from;
	struct fb_cmap_user cmap;
	struct fb_event event;
	void __user *argp = (void __user *)arg;
	long ret = 0;

	switch (cmd) {
	case FBIOGET_VSCREENINFO:
		if (!lock_fb_info(info))
			return -ENODEV;
		var = info->var;
		unlock_fb_info(info);

		ret = copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;
		break;
	case FBIOPUT_VSCREENINFO:
		if (copy_from_user(&var, argp, sizeof(var)))
			return -EFAULT;
		if (!lock_fb_info(info))
			return -ENODEV;
		console_lock();
		info->flags |= FBINFO_MISC_USEREVENT;
		ret = fb_set_var(info, &var);
		info->flags &= ~FBINFO_MISC_USEREVENT;
		console_unlock();
		unlock_fb_info(info);
		if (!ret && copy_to_user(argp, &var, sizeof(var)))
			ret = -EFAULT;
		break;
	case FBIOGET_FSCREENINFO:
		if (!lock_fb_info(info))
			return -ENODEV;
		fix = info->fix;
		unlock_fb_info(info);

		ret = copy_to_user(argp, &fix, sizeof(fix)) ? -EFAULT : 0;
		break;
	case FBIOPUTCMAP:
		if (copy_from_user(&cmap, argp, sizeof(cmap)))
			return -EFAULT;
		ret = fb_set_user_cmap(&cmap, info);
		break;
	case FBIOGETCMAP:
		if (copy_from_user(&cmap, argp, sizeof(cmap)))
			return -EFAULT;
		if (!lock_fb_info(info))
			return -ENODEV;
		cmap_from = info->cmap;
		unlock_fb_info(info);
		ret = fb_cmap_to_user(&cmap_from, &cmap);
		break;
	case FBIOPAN_DISPLAY:
		if (copy_from_user(&var, argp, sizeof(var)))
			return -EFAULT;
		if (!lock_fb_info(info))
			return -ENODEV;
		console_lock();
		ret = fb_pan_display(info, &var);
		console_unlock();
		unlock_fb_info(info);
		if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
			return -EFAULT;
		break;
	case FBIO_CURSOR:
		ret = -EINVAL;
		break;
	case FBIOGET_CON2FBMAP:
		if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
			return -EFAULT;
		if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
			return -EINVAL;
		con2fb.framebuffer = -1;
		event.data = &con2fb;
		if (!lock_fb_info(info))
			return -ENODEV;
		event.info = info;
		fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
		unlock_fb_info(info);
		ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
		break;
	case FBIOPUT_CON2FBMAP:
		if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
			return -EFAULT;
		if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
			return -EINVAL;
		if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
			return -EINVAL;
		if (!registered_fb[con2fb.framebuffer])
			request_module("fb%d", con2fb.framebuffer);
		if (!registered_fb[con2fb.framebuffer]) {
			ret = -EINVAL;
			break;
		}
		event.data = &con2fb;
		if (!lock_fb_info(info))
			return -ENODEV;
		event.info = info;
		ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
		unlock_fb_info(info);
		break;
	case FBIOBLANK:
		if (!lock_fb_info(info))
			return -ENODEV;
		console_lock();
		info->flags |= FBINFO_MISC_USEREVENT;
		ret = fb_blank(info, arg);
		info->flags &= ~FBINFO_MISC_USEREVENT;
		console_unlock();
		unlock_fb_info(info);
		break;
	default:
		if (!lock_fb_info(info))
			return -ENODEV;
		fb = info->fbops;
		if (fb->fb_ioctl)
			ret = fb->fb_ioctl(info, cmd, arg);
		else
			ret = -ENOTTY;
		unlock_fb_info(info)	}
	return ret;
}

 

如果对 ioctl 函数有所理解，可以很快看到 cmd 变量 FBIOGET_VSCREENINFO，这个变量就可以获得设备体 /dev/fb0 的相关的详细信息！

 

写的有点乱，主要是 CSDN 今天不知道为什么，总是保存不了，然我重新翻工了好几遍！上火了！