一个简单的framebuffer的显示使用例子

    本例子中，显示设备是一个oled的显示屏； 没有过多的关于分辨率，刷新频率的设置； 只是演示一个framebuffer的例子。

一， kernel层的驱动代码如下：

    1. 注册，这是一个使用i2c通讯的显示设备，因此注册成一个i2c设备。

          定义：

struct ssd1307fb_par {struct i2c_client *client;u32 height;struct fb_info *info;struct ssd1307fb_ops *ops;u32 page_offset;struct pwm_device *pwm;u32 pwm_period;int reset;int bklight;u32 width;};

static const struct i2c_device_id ssd1307fb_i2c_id[] = {{ "ssd1305fb", 0 },{ "ssd1306fb", 0 },{ "ssd1307fb", 0 },{ }};MODULE_DEVICE_TABLE(i2c, ssd1307fb_i2c_id);static struct i2c_driver ssd1307fb_driver = {.probe = ssd1307fb_probe,.remove = ssd1307fb_remove,.suspend = ssd1307fb_suspend,.resume = ssd1307fb_resume,.id_table = ssd1307fb_i2c_id,.driver = {.name = "ssd1307fb",.of_match_table = ssd1307fb_of_match,.owner = THIS_MODULE,},};module_i2c_driver(ssd1307fb_driver);

     2. 正常启动后进入probe() 函数， 进行初始化，包括变量的初始化，显示器件寄存器的初始化，和framebuffer的初始化等； 我们只列举关于framebuffer的初始化。

struct fb_info *info;struct device_node *node = client->dev.of_node;u32 vmem_size;struct ssd1307fb_par *par;u8 *vmem;int ret;

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

par->ops = (struct ssd1307fb_ops *)of_match_device(ssd1307fb_of_match,   &client->dev)->data;

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;

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);

       //   以上是对 info 变量的初始化，在我们的例子里，有一些，未必用到；

    memcpy(vmem, picture1, vmem_size);    ssd1305fb_update_display(par);    dev_info(&client->dev, "%s: have update display\n", __func__);ret = register_framebuffer(info);if (ret) {dev_err(&client->dev, "Couldn't register the framebuffer\n");goto panel_init_error;}

       //  上面是对共享内存的初始化和， 进行framebuffer的注册。

       //  在上面的注册中， 一些文件系统的定义如下：

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,};

        //   在上面的文件ops注册中， 虽然定义了 fb_read 和 fb_write 等文件节点，但在我们的例子中，这几个节点都没有用到。我们使用的是下面的 fb_deferred_io 的结构。
        //  在下面中， ssd1307fb_ssd1305_init  函数会被自动调用，进行oled显示设备的初始化。

static struct ssd1307fb_ops ssd1307fb_ssd1305_ops = {.init= ssd1307fb_ssd1305_init,};static struct ssd1307fb_ops ssd1307fb_ssd1306_ops = {.init= ssd1307fb_ssd1306_init,};static const struct of_device_id ssd1307fb_of_match[] = {{.compatible = "solomon,ssd1305fb-i2c",.data = (void *)&ssd1307fb_ssd1305_ops,},{.compatible = "solomon,ssd1306fb-i2c",.data = (void *)&ssd1307fb_ssd1306_ops,},{.compatible = "solomon,ssd1307fb-i2c",.data = (void *)&ssd1307fb_ssd1307_ops,},{},};MODULE_DEVICE_TABLE(of, ssd1307fb_of_match);

       //   针对共享内存的buff的初始化，如下：

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,};

       //    这样，当应用层更改共享内存的数据时，则 ssd1307fb_deferred_io()  函数会自动被调用； 从而调用ssd1305fb_update_display（）函数，进行显示的刷新。

二、 应用层的调用例子：

#include <unistd.h>#include <stdio.h>#include <string.h>#include <fcntl.h>#include <linux/fb.h>#include <sys/mman.h>#define SSD1307FB_SSD1305_MAX_COL128#define SSD1307FB_SSD1305_MAX_ROW64

unsigned char picture5[SSD1307FB_SSD1305_MAX_ROW/8][SSD1307FB_SSD1305_MAX_COL]={0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,...     ...

int main(){    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);    close(fbfd);    return 0;}