(OK) kernel create framebuffer device

http://blog.chinaunix.net/uid-26009923-id-4040712.html

一.framebuffer的初始化
1. 以s3cfb的注册过程说明
module_init(s3cfb_init);
   --> platform_driver_register(&s3cfb_driver);
         --> s3cfb_probe(struct platform_device *pdev)
 在drivers/video/samsung/s3cfb.c中

static int __init s3cfb_probe(struct platform_device
*pdev)
{
    //第一步为framebuffer分配空间
    struct fb_info *fbinfo 
= framebuffer_alloc(sizeof(s3cfb_info_t),
&pdev->dev);
    //第二步初始化fbinfo
    ....
    ....
    //第三步注册framebuffer
    ret = register_framebuffer(&s3cfb_info[index].fb);
}

2. framebuffer_alloc过程
在drivers/video/fbsysfs.c中,
主要作用就是: 申请内存,并略微初始化fb_info结构体,主要的初始化是在s3c_probe函数中

struct fb_info *framebuffer_alloc(size_t size, struct device
*dev)
{
    int fb_info_size 
= sizeof(struct fb_info);
    struct fb_info *info;
    fb_info_size += PADDING;   
//为了对齐
    //申请内存,并清零
    info = (struct fb_info
*) kzalloc(fb_info_size
+ size, GFP_KERNEL);
    info->par
= p + fb_info_size;
    //device指针保存dev
    info->device
= dev;
    return info;
}

3. register_framebuffer过程
在drivers/video/fbmem.c中
主要作用是:
     1. 在全局变量数组registered_fb中查找未使用的一项,把找到的这个项号保存在fb_info中
     2. 在/dev/graphics/fb目录下创建设备结点, /dev/graphics/fb0 ls /dev/graphics/fb1就产生了
     3. 将fb_info添加到全局数组registered_fb中,并发送msg,说明注册完成

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;

    if (fb_check_foreignness(fb_info))
        return -ENOSYS;

    remove_conflicting_framebuffers(fb_info->apertures, fb_info->fix.id,
 fb_is_primary_device(fb_info));

    num_registered_fb++;
    for (i
= 0 ; i 
< FB_MAX; i++)  
//1.1在数组registered_fb中搜索没有使用的一项来注册
        if (!registered_fb[i])
            break;
    fb_info->node
= i;             
//1.2这个i值很重要,以后open(/dev/fb0),后面的0,1,2就是这个i
    mutex_init(&fb_info->lock);
    mutex_init(&fb_info->mm_lock);
    //2.在"/dev/grapihc"下创建fb[i]设备文件,fb_class="/dev/graphic"
    fb_info->dev
= device_create(fb_class, fb_info->device, MKDEV(FB_MAJOR,
 i), 
NULL, "fb%d", i);
    fb_init_device(fb_info);  
//在/sys/device目录下创建/sys文件
    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;                  //3.将初始化了的fb_info加到全局变量中

    event.info 
= fb_info;
    if (!lock_fb_info(fb_info))
        return -ENODEV;
    fb_notifier_call_chain(FB_EVENT_FB_REGISTERED,
&event);
    unlock_fb_info(fb_info);
    return 0;
}

这样就注册好了framebuffer,有了/dev/graphics/fb0,但是文件操作在哪儿呢?
二.上层调用 open /dev/graphics/fb0时
通过register_framebuffer产生了设备文件/dev/graphics/fb0,但是open /dev/graphics/fb0时的文件操作是如何产生的呢?
看一下drivers/video/fbmem.c的注册过程就知道了.
module_init(fbmem_init);
    --> fbmem_init

static int __init
fbmem_init(void)
{
    proc_create("fb", 0,
NULL, 
&fb_proc_fops);    
//创建/proc/fb
    register_chrdev(FB_MAJOR,"fb",&fb_fops);   
    //注册字符设备文件
   //创建class=/dev/graphics",以后用device_create创建的设备文件都会在/dev/graphics目录下
    fb_class = class_create(THIS_MODULE,
"graphics");
    return 0;
}

注册的文件操作结构体是fb_fops

static const struct file_operations fb_fops
= {
    .owner =    THIS_MODULE,
    .mmap =        fb_mmap,
    .open =        fb_open,
    .... //省略
};

上层调用open /dev/graphics/fb0时,会先调用fb_open函数

static int fb_open(struct inode
*inode, struct file
*file)
__acquires(&info->lock)
__releases(&info->lock)
{
    //从inode中获取次设备号,来判断是哪个fb,并将次设备号转为索引值
    int fbidx 
= iminor(inode);
    struct fb_info *info;
    int res = 0;

    if (fbidx
>= FB_MAX)
        return -ENODEV;
    info = registered_fb[fbidx]; 
//通过索引值找在全局数组中找到fb
    if (!info)
        request_module("fb%d", fbidx);
    info = registered_fb[fbidx]; 
//通过索引值找在全局数组中找到fb
    if (!info)                    //为什么要调两次?
        return -ENODEV;
    mutex_lock(&info->lock);
    if (!try_module_get(info->fbops->owner))
{  //模块引用计数加1
        res = 
-ENODEV;
        goto out;
    }
    file->private_data
= info;
    if (info->fbops->fb_open)
{              //如果fb0有open函数则调用fb0的open
        res = info->fbops->fb_open(info,1);
        if (res)
            module_put(info->fbops->owner);
    }
#ifdef CONFIG_FB_DEFERRED_IO
    if (info->fbdefio)
        fb_deferred_io_open(info, inode, file);
#endif
out:
    mutex_unlock(&info->lock);
    return res;
}