本文主要是介绍omap 的framebuffer驱动程序，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1.帧缓冲的基本原理
通过 framebuffer ，应用程序用 mmap 把显存映射到应用程序虚拟地址空间，将要显示的数据写入这个内存空间就可以在屏幕上显示出来；
驱动程序分配系统内存作为显存；实现 file_operations 结构中的接口，为应用程序服务；实现 fb_ops 结构中的接口，控制和操作 LCD 控制器；
驱动程序将显存的起始地址和长度传给 LCD 控制器的寄存器 (一般由 fb_set_var 完成) 。 LCD 控制器会自动的将显存中的数据显示在 LCD 屏上。
2.
register_framebuffer(struct fb_info *fb_info)
unregister_framebuffer(struct fb_info *fb_info)
底层驱动程序的工作基本上是填充 fb_info 结构，然后注册它
3. OMAP 的 DSS显示
DSS（Display sub system）显示子系统
显示子系统的库在drivers/video/omap2/dss目录中，主要包含了
core.c, dispc.c, display.c, dpi.c, dss.c ,manager.c omapdss.c, overlay.c venc.c
core.c中定义了platform_driver
static struct platform_driver omap_dss_driver = {
.driver = {.name = "omapdss",.owner = THIS_MODULE,},
}
它和arch/arm/mach-omap2中定义的平台设备相匹配
static struct platform_device my_dss_device = {.name = "omapdss",.id = -1,.dev = {.platform_data = &my_dss_data,},
};
文件系统的信息包含在以下目录中
/ # ls sys/devices/platform/omapdss/
uevent
modalias
subsystem
power
driver
manager0
manager1
overlay0
overlay1
overlay2
microamps_requested_vdda_dac
display2
display1
display0
----------------------------------------------------
overlay0目录中为基本显示层的信息
overlay1和overlay2分别目录中分别是两个叠加显示层的信息
manager0和manager1中则提供了管理方面的功能
查看sys文件系统
/ # cat sys/devices/platform/omapdss/overlay0/name
gfx
gfx为graphics的含义，表示overlay0的名称为图形层,文件enable是一个可又控制的
# echo 0 > sys/devices/platform/omapdss/overlay0/enabled 关屏
# echo 1 > sys/devices/platform/omapdss/overlay0/enabled 开屏
4. 主显示驱动的framebuffer
drivers/video/omap2/omapfb
omafb.c, omapfb-sysfs.c, omapfb-ioctl.c, omapfb-main.c
omapfb-main.c定义了platform_driver
#define MODULE_NAME "omapfb"
static struct platform_driver omapfb_driver = {.probe = omapfb_probe,.remove = omapfb_remove,.suspend = omapfb_suspend,.resume = omapfb_resume,.driver = {.name = MODULE_NAME,.owner = THIS_MODULE,},
};
与arch/arm/plat-omap/fb.c中的platform_device相匹配
static struct platform_device omap_fb_device = {.name = "omapfb",.id = -1,.dev = {.dma_mask = &omap_fb_dma_mask,.coherent_dma_mask = ~(u32)0,.platform_data = &omapfb_config,},.num_resources = 0,
};
omapfb-main.c的调用
static int omapfb_probe(struct platform_device *pdev)
{struct omapfb2_device *fbdev = NULL;omapfb_create_framebuffers(fbdev);/*调用 framebuffer_alloc 为fb_info结构体分配内存*/
}
static int omapfb_create_framebuffers(struct omapfb2_device *fbdev)
{struct fb_info *fbi;struct omapfb2_device *fbdev = NULL;fbdev = kzalloc(sizeof(struct omapfb2_device), GFP_KERNEL);fbi = framebuffer_alloc(sizeof(struct omapfb_info),fbdev->dev);...omapfb_fb_init(fbdev, fbdev->fbs[i]);//初始化//注册framebufferfor (i = 0; i < fbdev->num_fbs; i++) {r = register_framebuffer(fbdev->fbs[i]);return r;}
}
static int omapfb_fb_init(struct omapfb2_device *fbdev, struct fb_info *fbi)
{fbi->fbops = &omapfb_ops;
}static struct fb_ops omapfb_ops = {.owner = THIS_MODULE,.fb_open = omapfb_open,.fb_release = omapfb_release,.fb_fillrect = cfb_fillrect,.fb_copyarea = cfb_copyarea,.fb_imageblit = cfb_imageblit,.fb_blank = omapfb_blank,.fb_ioctl = omapfb_ioctl,.fb_check_var = omapfb_check_var,.fb_set_par = omapfb_set_par,.fb_pan_display = omapfb_pan_display,.fb_mmap = omapfb_mmap,.fb_setcolreg = omapfb_setcolreg,.fb_setcmap = omapfb_setcmap,/*.fb_write = omapfb_write,*/
};
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