1.framebuffer驱动
2.spi framebuffer驱动
3.spi framebuffer驱动(切换并显示虚拟终端)

framebuffer驱动

framebuffer最基本的驱动只需要填充并注册fb_info结构体

struct fb_info {
	atomic_t count;
	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 */
#ifdef CONFIG_FB_BACKLIGHT
	/* assigned backlight device */
	/* set before framebuffer registration, 
	   remove after unregister */
	struct backlight_device *bl_dev;

	/* Backlight level curve */
	struct mutex bl_curve_mutex;	
	u8 bl_curve[FB_BACKLIGHT_LEVELS];
#endif
#ifdef CONFIG_FB_DEFERRED_IO
	struct delayed_work deferred_work;
	struct fb_deferred_io *fbdefio;
#endif
	struct fb_ops *fbops;
	struct device *device;		/* This is the parent */
	struct device *dev;		/* This is this fb device */
	int class_flag;                    /* private sysfs flags */
#ifdef CONFIG_FB_TILEBLITTING
	struct fb_tile_ops *tileops;    /* Tile Blitting */
#endif
	char __iomem *screen_base;	/* Virtual address */
	unsigned long screen_size;	/* Amount of ioremapped VRAM or 0 */ 
	void *pseudo_palette;		/* Fake palette of 16 colors */ 
#define FBINFO_STATE_RUNNING	0
#define FBINFO_STATE_SUSPENDED	1
	u32 state;			/* Hardware state i.e suspend */
	void *fbcon_par;                /* fbcon use-only private area */
	/* From here on everything is device dependent */
	void *par;
	/* we need the PCI or similar 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;
};

参数比较多，不解释，看一个范例

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fb.h>
#include <linux/dma-mapping.h>

#define X 1024
#define Y 768

u32 p_addr; //用于存放显存的物理地址
u8 *v_addr; //用于存放显存的虚拟地址, 在驱动代码，我们也只能操作缓存的虚拟地址

struct fb_ops fops = { //这里不实现操作函数，使用fbmem.c里实现的功能函数
               //如果这里实现了功能函数，则会调用这里实现的函数
};

struct fb_info *fbi;
static int __init framebuffer_init(void)
{
    v_addr = dma_alloc_coherent(NULL, X*Y*4, &p_addr, GFP_KERNEL); //分配显存的缓冲区

    //动态分配fb_info的对象空间,　而且额外分配100个字节(这100字节空间的地址==&fbi[1])
    fbi = framebuffer_alloc(100, NULL);

    fbi->var.xres = X; //分辨率
    fbi->var.yres = Y;
    fbi->var.xres_virtual = X;
    fbi->var.yres_virtual = Y;
    fbi->var.bits_per_pixel = 32; // 32位每个像素
    fbi->var.red.offset = 16; //像素数据里的红
    fbi->var.red.length = 8;
    fbi->var.green.offset = 8; //像素数据里的绿
    fbi->var.green.length = 8;
    fbi->var.blue.offset = 0; //像素数据里的蓝
    fbi->var.blue.length = 8;

    strcpy(fbi->fix.id, "myfb"); 
    fbi->fix.smem_start = p_addr; //显存的物理地址
    fbi->fix.smem_len = X*Y*4; //显存缓冲区大小
    fbi->fix.type = FB_TYPE_PACKED_PIXELS; //像素数据是打包的方式
    fbi->fix.visual = FB_VISUAL_TRUECOLOR; //真彩色
    fbi->fix.line_length = X*4; //每一行多少个字节

    fbi->fbops = &fops; 
    fbi->screen_base = v_addr; // 显示缓冲区的虚拟地址
    fbi->screen_size = X*Y*4;


    return register_framebuffer(fbi); //注册fb设备
}

static void __exit framebuffer_exit(void)
{
    unregister_framebuffer(fbi);
    framebuffer_release(fbi);

    dma_free_coherent(NULL, X*Y*4, v_addr, p_addr);
}

module_init(framebuffer_init);
module_exit(framebuffer_exit);

MODULE_LICENSE("GPL");

fb内存缓冲区使用dma_alloc_coherent申请物理连续大内存。使用register_framebuffer注册结构体就完成了framebuffer设备的注册，/dev目录下可以看到生成了一个新的fb设备。