Linux-FrameBuffer fb_info结构体解析申请以及注册
fb_info 结构体(fb.h(include/linux))
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
union {
char __iomem *screen_base; /* Virtual address */
char *screen_buffer;
};
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;
bool skip_vt_switch; /* no VT switch on suspend/resume required */
};
- count:fb_info的引用计数，fb_open 时使其加1，release时使其减1，为0时，destroy
- node:全局变量
registered_fb中的索引值，注册的时候分配，通过node可以索引fb_info - flags:一些标志位，有关于硬件加速的，大小端，fb的内存位置(设备或者内存)，具体硬件加速的方法，表明哪个使用了硬件加速
#define FBINFO_MODULE 0x0001 /* Low-level driver is a module */
#define FBINFO_HWACCEL_DISABLED 0x0002
/* When FBINFO_HWACCEL_DISABLED is set:
* Hardware acceleration is turned off. Software implementations
* of required functions (copyarea(), fillrect(), and imageblit())
* takes over; acceleration engine should be in a quiescent state */
/* hints */
#define FBINFO_VIRTFB 0x0004 /* FB is System RAM, not device. */
#define FBINFO_PARTIAL_PAN_OK 0x0040 /* otw use pan only for double-buffering */
#define FBINFO_READS_FAST 0x0080 /* soft-copy faster than rendering */
/* hardware supported ops */
/* semantics: when a bit is set, it indicates that the operation is
* accelerated by hardware.
* required functions will still work even if the bit is not set.
* optional functions may not even exist if the flag bit is not set.
*/
#define FBINFO_HWACCEL_NONE 0x0000
#define FBINFO_HWACCEL_COPYAREA 0x0100 /* required */
#define FBINFO_HWACCEL_FILLRECT 0x0200 /* required */
#define FBINFO_HWACCEL_IMAGEBLIT 0x0400 /* required */
#define FBINFO_HWACCEL_ROTATE 0x0800 /* optional */
#define FBINFO_HWACCEL_XPAN 0x1000 /* optional */
#define FBINFO_HWACCEL_YPAN 0x2000 /* optional */
#define FBINFO_HWACCEL_YWRAP 0x4000 /* optional */
#define FBINFO_MISC_USEREVENT 0x10000 /* event request
from userspace */
#define FBINFO_MISC_TILEBLITTING 0x20000 /* use tile blitting */
/* A driver may set this flag to indicate that it does want a set_par to be
* called every time when fbcon_switch is executed. The advantage is that with
* this flag set you can really be sure that set_par is always called before
* any of the functions dependent on the correct hardware state or altering
* that state, even if you are using some broken X releases. The disadvantage
* is that it introduces unwanted delays to every console switch if set_par
* is slow. It is a good idea to try this flag in the drivers initialization
* code whenever there is a bug report related to switching between X and the
* framebuffer console.
*/
#define FBINFO_MISC_ALWAYS_SETPAR 0x40000
/* where the fb is a firmware driver, and can be replaced with a proper one */
#define FBINFO_MISC_FIRMWARE 0x80000
/*
* Host and GPU endianness differ.
*/
#define FBINFO_FOREIGN_ENDIAN 0x100000
/*
* Big endian math. This is the same flags as above, but with different
* meaning, it is set by the fb subsystem depending FOREIGN_ENDIAN flag
* and host endianness. Drivers should not use this flag.
*/
#define FBINFO_BE_MATH 0x100000
/* report to the VT layer that this fb driver can accept forced console
output like oopses */
#define FBINFO_CAN_FORCE_OUTPUT 0x200000
- var:变量，描述的是具体屏的一些参数，包括可见的分辨率，Bpp(bits_per_pixel),还有具体的时钟信号，包括bp，fp，vsync，hsync等,可以通过应用层设置也可以驱动层配置，相关设置时序的工具有fbset，还有相关的一些调色板配置
- fix:描述的是不可变量，驱动中控制参数，不能在用户层更改。包括显存起始位置（一般是显示控制器DMA起始地址-物理地址,smem_start），framebuffer的长度(smem_len)
- monspecs:描述的是显示器的一些参数，时序，生产日期等，一般这种信息描述在显示器中的EDID中，通过解析EDID来填充此参数
- queue：事件队列，不过分析多个驱动，并没有发现使用该字段的，等遇到再做更新
- pixmap，sprite（光标）都是像素图，注册framebuffer的时候会默认申请，未知干什么用的
- cmap：设备独立的 colormap 信息，可以通过 ioctl 的 FBIOGETCMAP 和 FBIOPUTCMAP 命令设置 colormap；
- modelist:将var参数转化成video mode，然后存入这个链表
- mode：一些时序，刷新率扫描方式(vmode)（隔行，逐行），极性(sync)
- 关于背光CONFIG_FB_BACKLIGHT，有关于背光曲线以及背光设备注册，需要注意的是需要在注册framebuffer之前就对其初始化
- CONFIG_FB_DEFERRED_IO，延迟IO，使用缺页中断的原理操作，减少FBIOPAN_DISPLAY带来的系统调用开支。原理
- fbops:提供具体的fb操作函数，主要是通过fbmem.c中提供的文件操作函数，间接调用fb_ops,主要的操作有fb_check_var，fb_pan_display，fb_mmap，等，以下三个函数提供了绘图的操作，可以使用系统中的绘图函数，也可以重写硬件加速的绘图函数
/* 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);
- device:fb_info的设备父节点，对应即sys/device/xxx/fb_info
- dev：设备指针，注册framebuffer时创建
- pseudo_palette：伪调色板
- state：硬件状态，在fbmem中会设置成suspend以及resume
#define FBINFO_STATE_RUNNING 0
#define FBINFO_STATE_SUSPENDED 1
19.skip_vt_switch:关于VT switch，是与console切换以及PM相关的，具体
framebuffer的申请
struct fb_info * framebuffer_alloc(size_t size, struct device *dev)
struct fb_info *framebuffer_alloc(size_t size, struct device *dev)
{
#define BYTES_PER_LONG (BITS_PER_LONG/8)
#define PADDING (BYTES_PER_LONG - (sizeof(struct fb_info) % BYTES_PER_LONG))
int fb_info_size = sizeof(struct fb_info);
struct fb_info *info;
char *p;
if (size)
fb_info_size += PADDING;
p = kzalloc(fb_info_size + size, GFP_KERNEL);
if (!p)
return NULL;
info = (struct fb_info *) p;
if (size)
info->par = p + fb_info_size;
info->device = dev;
#ifdef CONFIG_FB_BACKLIGHT
mutex_init(&info->bl_curve_mutex);
#endif
return info;
#undef PADDING
#undef BYTES_PER_LONG
}
EXPORT_SYMBOL(framebuffer_alloc);
- 位置
fbsysfs.c video\fbdev\core - 功能
申请fb_info,初始化其内部的少许成员(device,par,bl_curve_mutex(CONFIG_FB_BACKLIGHT)) - 传入参数
size：除了fb_info的结构体申请之外，多申请的字节数，将多申请的首地址赋值给par，假如为0，则不用顾及par，为NULL，也不会涉及到字节对齐
device：赋值fb_info中device，作为fb_info的父节点存在，表现是sysfs中的子目录与父目录关系
framebuffer注册
int register_framebuffer(struct fb_info *fb_info)
static int do_register_framebuffer(struct fb_info *fb_info)
{
int i, ret;
struct fb_event event;
struct fb_videomode mode;
if (fb_check_foreignness(fb_info))
return -ENOSYS;
ret = do_remove_conflicting_framebuffers(fb_info->apertures,
fb_info->fix.id,
fb_is_primary_device(fb_info));
if (ret)
return ret;
if (num_registered_fb == FB_MAX)
return -ENXIO;
num_registered_fb++;
for (i = 0 ; i < FB_MAX; i++)
if (!registered_fb[i])
break;
fb_info->node = i;
atomic_set(&fb_info->count, 1);
mutex_init(&fb_info->lock);
mutex_init(&fb_info->mm_lock);
fb_info->dev = device_create(fb_class, fb_info->device,
MKDEV(FB_MAJOR, i), NULL, "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);
if (fb_info->skip_vt_switch)
pm_vt_switch_required(fb_info->dev, false);
else
pm_vt_switch_required(fb_info->dev, true);
fb_var_to_videomode(&mode, &fb_info->var);
fb_add_videomode(&mode, &fb_info->modelist);
registered_fb[i] = fb_info;
event.info = fb_info;
if (!lockless_register_fb)
console_lock();
if (!lock_fb_info(fb_info)) {
if (!lockless_register_fb)
console_unlock();
return -ENODEV;
}
fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
unlock_fb_info(fb_info);
if (!lockless_register_fb)
console_unlock();
return 0;
}
-
作用
注册framebuffer到framebuffer框架下的全局变量registered_fb中 -
framebuffer的框架(框架图抄来的)
在framebuffer框架中(fbmem.c)，完成了对字符设备的注册，申请了Major=29(FB_MAJOR),此设备号从0开始，总共256（实际上只支持32个#define FB_MAX 32 /* sufficient for now */）的设备数,并提供了f_ops,
ret = register_chrdev(FB_MAJOR, "fb", &fb_fops);
static const struct file_operations fb_fops = {
.owner = THIS_MODULE,
.read = fb_read,
.write = fb_write,
.unlocked_ioctl = fb_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = fb_compat_ioctl,
#endif
.mmap = fb_mmap,
.open = fb_open,
.release = fb_release,
#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
.get_unmapped_area = get_fb_unmapped_area,
#endif
#ifdef CONFIG_FB_DEFERRED_IO
.fsync = fb_deferred_io_fsync,
#endif
.llseek = default_llseek,
};
- 注册成功的结果
1.添加到全局变量registered_fb数组中，其索引号赋值给fb_info中的node 成员变量
2.索引号作为次设备号，创建/dev/fb%d的设备节点，%d 是次设备号
fb_info->dev = device_create(fb_class, fb_info->device, MKDEV(FB_MAJOR, i), NULL, "fb%d", i);
3.在其/sys/xxx/下创建一系列的属性文件（由fb_init_device完成），其中xxx包含父节点的目录
static struct device_attribute device_attrs[] = {
__ATTR(bits_per_pixel, S_IRUGO|S_IWUSR, show_bpp, store_bpp),
__ATTR(blank, S_IRUGO|S_IWUSR, show_blank, store_blank),
__ATTR(console, S_IRUGO|S_IWUSR, show_console, store_console),
__ATTR(cursor, S_IRUGO|S_IWUSR, show_cursor, store_cursor),
__ATTR(mode, S_IRUGO|S_IWUSR, show_mode, store_mode),
__ATTR(modes, S_IRUGO|S_IWUSR, show_modes, store_modes),
__ATTR(pan, S_IRUGO|S_IWUSR, show_pan, store_pan),
__ATTR(virtual_size, S_IRUGO|S_IWUSR, show_virtual, store_virtual),
__ATTR(name, S_IRUGO, show_name, NULL),
__ATTR(stride, S_IRUGO, show_stride, NULL),
__ATTR(rotate, S_IRUGO|S_IWUSR, show_rotate, store_rotate),
__ATTR(state, S_IRUGO|S_IWUSR, show_fbstate, store_fbstate),
#ifdef CONFIG_FB_BACKLIGHT
__ATTR(bl_curve, S_IRUGO|S_IWUSR, show_bl_curve, store_bl_curve),
#endif
};
4.初始化pixmap的成员变量，具体要干什么未知，后面更新
5.将var的中的屏的参数转换成fb_videomode,将其mode挂载在modelist链表中去，当然首次会初始化modelist
INIT_LIST_HEAD(&fb_info->modelist);
6.skip_vt_switch,主要是console在suspend的时候切换console，调用
pm_vt_switch_required(fb_info->dev, false);完成。设置为1，则不进行切换，当然也要使能对应的CONFIG，CONFIG_VT_CONSOLE_SLEEP
7.通过通知链，将FB_EVENT_FB_REGISTERED的事件发送出去，通知链的原理是建立一个链表，向其注册回调，通过xxx_notifier_call_chain,将事件发送出去，这个通知链会经常用到，通知一些包括RESUME，SUSPEND，BLANK等事件，具体实现在fb_notify.c
总结
1.fb_info代表的一类显示设备(LCD,OLED等)，而显示设备的父节点就是显示控制器，
2.通常显示设备的参数以及显示控制器参数会在deviceTree中描述，对于显示设备来讲，描述的是一些时序，对应到fb_info中var参数，控制器参数一般包括显示控制器的中断号，显存位置等
3.显示控制器作为设备挂在platform device的树中，显示控制器驱动 platform driver 通过匹配某些字段，完成match操作，probe函数中，读取平台参数，包括显示控制器的参数，显示设备的参数，调用注册framebuffer，完成设备节点的创建
4.显示控制器一般会关联硬件加速函数，2D,可以部分重写部分framebuffer框架中的一些绘图函数
5.Framebuffer框架作为简单的显示框架，目前已经切换到DRM框架中，为了适应更复杂的图形计算。目前主流的芯片也都基于其框架写显示部分的驱动。但是早期的芯片例如三星2440,6410 还是会有部分的驱动代码
6.DRM框架也是今后的方向