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_COL 128
#define SSD1307FB_SSD1305_MAX_ROW 64

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;
}