怎样通过framebuffer来传递关屏信息-白红宇

怎样通过framebuffer来传递关屏信息

阅读量：4283 次

发布时间：2019-05-27

本文共 3541 字，大约阅读时间需要 11 分钟。

本人的项目是一个用oled来显示的android项目；需要在系统睡眠关闭主屏幕的时候，一起把oled屏幕关掉。但这是并没有进入系统睡眠。因此不能使用kernel里的suspend 与resume机制来控制oled的显示和背光。可以使用framebuffer的功能来从用户态到kernel态来传递命令。

在用户层，可以使用消息的机制，来获得用户关屏的动作，无论是短按电源键还是时间到关屏，都会有一个消息发布；这是上层hardware从可以获得这个消息，然后通过framebuffer来告知kernel层；本文主要说明这个用户层和kernel之间的通信机制。

一. kernel对framebuffer的注册和使用

1. probe函数里的变量定义：

struct fb_info *info;	u32 vmem_size;	struct ssd1307fb_par *par;	u8 *vmem;

2. 主要变量的初始化：（只有部分）

info = framebuffer_alloc(sizeof(struct ssd1307fb_par), &client->dev);	if (!info) {		dev_err(&client->dev, "Couldn't allocate framebuffer.\n");		return -ENOMEM;	}

vmem_size = par->width * par->height / 8;	vmem = vmalloc(vmem_size);	if (!vmem) {		dev_err(&client->dev, "Couldn't allocate graphical memory.\n");		ret = -ENOMEM;		goto fb_alloc_error;	}	info->fbops = &ssd1307fb_ops;	info->fix = ssd1307fb_fix;	info->fix.line_length = par->width / 8;	info->fbdefio = &ssd1307fb_defio;	dev_info(&client->dev, "%s info->fix.line_length=%d\n",        __func__, info->fix.line_length);	info->var = ssd1307fb_var;	info->var.xres = par->width;	info->var.xres_virtual = par->width;	info->var.yres = par->height;	info->var.yres_virtual = par->height;	info->var.red.length = 1;	info->var.red.offset = 0;	info->var.green.length = 1;	info->var.green.offset = 0;	info->var.blue.length = 1;	info->var.blue.offset = 0;	info->screen_base = (char *)vmem;	info->fix.smem_start = (unsigned long)vmem;	info->fix.smem_len = vmem_size;	fb_deferred_io_init(info);

3. 注册

ret = register_framebuffer(info);	if (ret) {		dev_err(&client->dev, "Couldn't register the framebuffer\n");		goto panel_init_error;	}

4. 在上面的注册中，还有一些文件节点需要定义：

static struct fb_fix_screeninfo ssd1307fb_fix = {	.id		= "Solomon SSD1307",	.type		= FB_TYPE_PACKED_PIXELS,	.visual		= FB_VISUAL_MONO10,	.xpanstep	= 0,	.ypanstep	= 0,	.ywrapstep	= 0,	.accel		= FB_ACCEL_NONE,};static struct fb_var_screeninfo ssd1307fb_var = {	.bits_per_pixel	= 1,};

static struct fb_ops ssd1307fb_ops = {	.owner		= THIS_MODULE,	.fb_read	= fb_sys_read,	.fb_write	= ssd1307fb_write,	.fb_fillrect	= ssd1307fb_fillrect,	.fb_copyarea	= ssd1307fb_copyarea,	.fb_imageblit	= ssd1307fb_imageblit,	.fb_blank   = ssd1305fb_blank,};

static void ssd1307fb_deferred_io(struct fb_info *info,				struct list_head *pagelist){	ssd1305fb_update_display(info->par);}static struct fb_deferred_io ssd1307fb_defio = {	.delay		= HZ,	.deferred_io	= ssd1307fb_deferred_io,};

在上面的注册中， .fb_blank = ssd1305fb_blank, 就是对关屏动作的回调函数的调用。

二、上层对framebuffer的调用

int fbfd = 0;    struct fb_var_screeninfo vinfo;    struct fb_fix_screeninfo finfo;    long int screensize = 0;    char *fbp = 0;    // Open the file for reading and writing    fbfd = open("/dev/graphics/fb3", O_RDWR);    if (fbfd < 0) {        printf("Error: cannot open framebuffer device.\n");        exit(1);    }    printf("The framebuffer device was opened successfully. fbfd=%x\n", fbfd);    screensize = 128 * 8;    printf("the screensize is %d\n", screensize );    // Map the device to memory    fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,                       fbfd, 0);    if ((int)fbp == -1) {        printf("Error: failed to map framebuffer device to memory.\n");        exit(4);    }    printf("The framebuffer device was mapped to memory successfully.\n");    memcpy(fbp, picture5, screensize);    munmap(fbp, screensize);	sleep(10);    printf("start blank OLED\n");	ioctl(fbfd, FBIOBLANK, 0);  // enable bklight	ioctl(fbfd, FBIOBLANK, 1);  // disable bkilght    close(fbfd);

在上面中，ioctl(fbfd, FBIOBLANK, 0) ; 函数就是对底层函数ssd1305fb_blank（）的调用。

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