S3C2440 (3.5寸)LCD驱动程序之层次分析（十六）

http://www.cnblogs.com/lifexy/p/7603327.html

如果我们的系统用GUI（图形界面接口），这是LCD设备驱动程序就应该编写成frambuffer接口，而不是像之前那样只编写操作底层的LCD控制器接口。

什么是frambuffer设备？

    frambuffer设备层是对图像设备的一种抽象，它代表了视频硬件的帧缓存，使得应用程序通过定义好的接口就可以访问硬件。所以应用程序不需要考虑底层的（寄存器级）的操作。应用程序对设备文件的访问一般在/dev目录，如/dev/fb*。

内核的frambuffer在drivers/video/fbmem.c(fb：frame buffer)

1、我们进入fbmem.c找到它的入口函数：

fbmem_init(void)
{
	create_proc_read_entry("fb", 0, NULL, fbmem_read_proc, NULL);

	if (register_chrdev(FB_MAJOR,"fb",&fb_fops))    //（1）创建字符设备
		printk("unable to get major %d for fb devs\n", FB_MAJOR);

	fb_class = class_create(THIS_MODULE, "graphics");    //创建类
	if (IS_ERR(fb_class)) {
		printk(KERN_WARNING "Unable to create fb class; errno = %ld\n", PTR_ERR(fb_class));
		fb_class = NULL;
	}
	return 0;
}

（1）创建字符设备"fb"，FB_MAJOR=29,主设备号为29，使用命令cat /proc/devices找到这个字符设备

和我们之前的驱动程序一样，但是没有创建设备节点，为什么？

因为需要注册了LCD驱动后，才会有设备节点，所以这里的代码没有，后面分析哪里有。

2、我们来看看注册的file_operations结构体fb_ops的.open函数和.read函数，应用层是如何打开驱动，读取驱动数据

2.1 fb_open函数如下：

fb_open(struct inode *inode, struct file *file)
{
	int fbidx = iminor(inode);    //获取设备节点的次设备号
	struct fb_info *info;            //定义fb_info结构体
	int res = 0;

	if (fbidx >= FB_MAX)
		return -ENODEV;
#ifdef CONFIG_KMOD
	if (!(info = registered_fb[fbidx]))    //(1)获取此设备的LCD驱动信息
		try_to_load(fbidx);
#endif /* CONFIG_KMOD */
	if (!(info = registered_fb[fbidx]))
		return -ENODEV;
	if (!try_module_get(info->fbops->owner))
		return -ENODEV;
	file->private_data = info;
	if (info->fbops->fb_open) {    //调用register_fb[fbidx]->fbops->fb_open
		res = info->fbops->fb_open(info,1);
		if (res)
			module_put(info->fbops->owner);
	}
	return res;
}

（1）register_fb[fbidx]这个数组也是fb_info结构体，其中fbidx等于次设备号id，显然这个数组就是保存我们各个LCD驱动的信息。

2.2 fb_read函数如下：

fb_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
	unsigned long p = *ppos;
	struct inode *inode = file->f_path.dentry->d_inode;
	int fbidx = iminor(inode);        //获取设备号
	struct fb_info *info = registered_fb[fbidx];    //获取设备号的lcd驱动信息
	u32 *buffer, *dst;
	u32 __iomem *src;
	int c, i, cnt = 0, err = 0;
	unsigned long total_size;

	if (!info || ! info->screen_base)
		return -ENODEV;

	if (info->state != FBINFO_STATE_RUNNING)
		return -EPERM;

	if (info->fbops->fb_read)
		return info->fbops->fb_read(info, buf, count, ppos);
	
	total_size = info->screen_size;    //获取屏幕长度

	if (total_size == 0)
		total_size = info->fix.smem_len;

	if (p >= total_size)
		return 0;

	if (count >= total_size)
		count = total_size;

	if (count + p > total_size)
		count = total_size - p;

	buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,    //分配缓冲区
			 GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;

	src = (u32 __iomem *) (info->screen_base + p);    //获得显存物理地址

	if (info->fbops->fb_sync)
		info->fbops->fb_sync(info);

	while (count) {
		c  = (count > PAGE_SIZE) ? PAGE_SIZE : count;    //获得页地址
		dst = buffer;
		for (i = c >> 2; i--; )
			*dst++ = fb_readl(src++);    //读取显存每个像素点数据，放到dst地址上
		if (c & 3) {
			u8 *dst8 = (u8 *) dst;
			u8 __iomem *src8 = (u8 __iomem *) src;

			for (i = c & 3; i--;)
				*dst8++ = fb_readb(src8++);

			src = (u32 __iomem *) src8;
		}

		if (copy_to_user(buf, buffer, c)) {    //上传数据，长度等于页地址大小
			err = -EFAULT;
			break;
		}
		*ppos += c;
		buf += c;
		cnt += c;
		count -= c;
	}

	kfree(buffer);

	return (err) ? err : cnt;
}

从.open和.write函数中可以发现，都依赖于fb_info帧缓冲信息结构体，它从registed_fb[index]数组中得到，这个数组保存我们各个lcd驱动的信息。

3、我们来找找这个数组在哪里被注册，位于register_frambuffer()：

int
register_framebuffer(struct fb_info *fb_info)
{
	int i;
	struct fb_event event;
	struct fb_videomode mode;

	if (num_registered_fb == FB_MAX)
		return -ENXIO;
	num_registered_fb++;
	for (i = 0 ; i < FB_MAX; i++)    //查找空的数组
		if (!registered_fb[i])
			break;
	fb_info->node = i;
        //创建设备节点，名称为fbi，主设备号为29，次设备号为i
	fb_info->dev = device_create(fb_class, fb_info->device,
				     MKDEV(FB_MAJOR, i), "fb%d", i);
	if (IS_ERR(fb_info->dev)) {
		/* Not fatal */
		printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n", i, PTR_ERR(fb_info->dev));
		fb_info->dev = NULL;
	} else
		fb_init_device(fb_info);

	if (fb_info->pixmap.addr == NULL) {
		fb_info->pixmap.addr = kmalloc(FBPIXMAPSIZE, GFP_KERNEL);
		if (fb_info->pixmap.addr) {
			fb_info->pixmap.size = FBPIXMAPSIZE;
			fb_info->pixmap.buf_align = 1;
			fb_info->pixmap.scan_align = 1;
			fb_info->pixmap.access_align = 32;
			fb_info->pixmap.flags = FB_PIXMAP_DEFAULT;
		}
	}	
	fb_info->pixmap.offset = 0;

	if (!fb_info->pixmap.blit_x)
		fb_info->pixmap.blit_x = ~(u32)0;

	if (!fb_info->pixmap.blit_y)
		fb_info->pixmap.blit_y = ~(u32)0;

	if (!fb_info->modelist.prev || !fb_info->modelist.next)
		INIT_LIST_HEAD(&fb_info->modelist);

	fb_var_to_videomode(&mode, &fb_info->var);
	fb_add_videomode(&mode, &fb_info->modelist);
	registered_fb[i] = fb_info;

	event.info = fb_info;
	fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
	return 0;
}

得出这个register_frambuffer()除了注册fb_info，还创建了设备节点。

所以要注册驱动时就调用这个，如下图所示

4、我们来看看/dirvers/video/s3c2410fb.c中又是怎么实现驱动的

4.1 先找到入口和出口函数：

int __devinit s3c2410fb_init(void)
{
	return platform_driver_register(&s3c2410fb_driver);
}

static void __exit s3c2410fb_cleanup(void)
{
	platform_driver_unregister(&s3c2410fb_driver);
}

发现是注册、注销设备平台drv

4.2 来查看s3c2410fb_driver 如何定义的

static struct platform_driver s3c2410fb_driver = {
	.probe		= s3c2410fb_probe,
	.remove		= s3c2410fb_remove,
	.suspend	= s3c2410fb_suspend,
	.resume		= s3c2410fb_resume,
	.driver		= {
		.name	= "s3c2410-lcd",
		.owner	= THIS_MODULE,
	},
};

和我们上节分析的platform机制一样，当与设备匹配成功，就会进入probe函数，初始化驱动设备。

4.3 来看看.probe函数，如何实现驱动的

static int __init s3c2410fb_probe(struct platform_device *pdev)
{
	struct s3c2410fb_info *info;
	struct fb_info	   *fbinfo;
	struct s3c2410fb_hw *mregs;
	int ret;
	int irq;
	int i;
	u32 lcdcon1;

	mach_info = pdev->dev.platform_data;    //获取LCD设备信息（长度、类型等）
	if (mach_info == NULL) {
		dev_err(&pdev->dev,"no platform data for lcd, cannot attach\n");
		return -EINVAL;
	}

	mregs = &mach_info->regs;

	irq = platform_get_irq(pdev, 0);
	if (irq < 0) {
		dev_err(&pdev->dev, "no irq for device\n");
		return -ENOENT;
	}

	fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);//1、分配一个fb_info结构体
	if (!fbinfo) {
		return -ENOMEM;
	}

        //2、设置fb_info
	info = fbinfo->par;
	info->fb = fbinfo;
	info->dev = &pdev->dev;

	platform_set_drvdata(pdev, fbinfo);

	dprintk("devinit\n");

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

	memcpy(&info->regs, &mach_info->regs, sizeof(info->regs));

	/* Stop the video and unset ENVID if set */
	info->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID;
	lcdcon1 = readl(S3C2410_LCDCON1);
	writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, S3C2410_LCDCON1);

	info->mach_info		    = pdev->dev.platform_data;

	fbinfo->fix.type	    = FB_TYPE_PACKED_PIXELS;
	fbinfo->fix.type_aux	    = 0;
	fbinfo->fix.xpanstep	    = 0;
	fbinfo->fix.ypanstep	    = 0;
	fbinfo->fix.ywrapstep	    = 0;
	fbinfo->fix.accel	    = FB_ACCEL_NONE;

	fbinfo->var.nonstd	    = 0;
	fbinfo->var.activate	    = FB_ACTIVATE_NOW;
	fbinfo->var.height	    = mach_info->height;
	fbinfo->var.width	    = mach_info->width;
	fbinfo->var.accel_flags     = 0;
	fbinfo->var.vmode	    = FB_VMODE_NONINTERLACED;

	fbinfo->fbops		    = &s3c2410fb_ops;
	fbinfo->flags		    = FBINFO_FLAG_DEFAULT;
	fbinfo->pseudo_palette      = &info->pseudo_pal;

	fbinfo->var.xres	    = mach_info->xres.defval;
	fbinfo->var.xres_virtual    = mach_info->xres.defval;
	fbinfo->var.yres	    = mach_info->yres.defval;
	fbinfo->var.yres_virtual    = mach_info->yres.defval;
	fbinfo->var.bits_per_pixel  = mach_info->bpp.defval;

	fbinfo->var.upper_margin    = S3C2410_LCDCON2_GET_VBPD(mregs->lcdcon2) + 1;
	fbinfo->var.lower_margin    = S3C2410_LCDCON2_GET_VFPD(mregs->lcdcon2) + 1;
	fbinfo->var.vsync_len	    = S3C2410_LCDCON2_GET_VSPW(mregs->lcdcon2) + 1;

	fbinfo->var.left_margin	    = S3C2410_LCDCON3_GET_HFPD(mregs->lcdcon3) + 1;
	fbinfo->var.right_margin    = S3C2410_LCDCON3_GET_HBPD(mregs->lcdcon3) + 1;
	fbinfo->var.hsync_len	    = S3C2410_LCDCON4_GET_HSPW(mregs->lcdcon4) + 1;

	fbinfo->var.red.offset      = 11;
	fbinfo->var.green.offset    = 5;
	fbinfo->var.blue.offset     = 0;
	fbinfo->var.transp.offset   = 0;
	fbinfo->var.red.length      = 5;
	fbinfo->var.green.length    = 6;
	fbinfo->var.blue.length     = 5;
	fbinfo->var.transp.length   = 0;
	fbinfo->fix.smem_len        =	mach_info->xres.max *
					mach_info->yres.max *
					mach_info->bpp.max / 8;

	for (i = 0; i < 256; i++)
		info->palette_buffer[i] = PALETTE_BUFF_CLEAR;

	if (!request_mem_region((unsigned long)S3C24XX_VA_LCD, SZ_1M, "s3c2410-lcd")) {
		ret = -EBUSY;
		goto dealloc_fb;
	}


	dprintk("got LCD region\n");
        //3、硬件相关的操作，设置中断，LCD时钟频率，显存地址，配置银奖
	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_mem;
	}

	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);

	/* Initialize video memory */
	ret = s3c2410fb_map_video_memory(info);    //显存地址
	if (ret) {
		printk( KERN_ERR "Failed to allocate video RAM: %d\n", ret);
		ret = -ENOMEM;
		goto release_clock;
	}
	dprintk("got video memory\n");

	ret = s3c2410fb_init_registers(info);    //设置寄存器，配置引脚

	ret = s3c2410fb_check_var(&fbinfo->var, fbinfo);

	ret = register_framebuffer(fbinfo);    //4、注册一个fb_info结构体
	if (ret < 0) {
		printk(KERN_ERR "Failed to register framebuffer device: %d\n", ret);
		goto free_video_memory;
	}

	/* create device files */
	device_create_file(&pdev->dev, &dev_attr_debug);

	printk(KERN_INFO "fb%d: %s frame buffer device\n",
		fbinfo->node, fbinfo->fix.id);

	return 0;

free_video_memory:
	s3c2410fb_unmap_video_memory(info);
release_clock:
	clk_disable(info->clk);
	clk_put(info->clk);
release_irq:
	free_irq(irq,info);
release_mem:
 	release_mem_region((unsigned long)S3C24XX_VA_LCD, S3C24XX_SZ_LCD);
dealloc_fb:
	framebuffer_release(fbinfo);
	return ret;
}

4.4 显然要写个LCD驱动程序，需要以下4步：

1）分配一个fb_info结构体：framebuffer_alloc（）；

2）设置fb_info；

3）硬件相关操作（设置中断，LCD时钟频率，显存地址，配置引脚… …）

4）注册fb_info：register_frambuffer（）