详解linux lcd驱动编写

有些嵌入式设备是不需要lcd的，比如路由器。但是，还有些设备是需要lcd显示内容的，比如游戏机、测试仪、智能手表等等。所以，今天我们就看看lcd驱动在linux上是怎么进行的。

1、代码目录

drivers/video

2、查看video下的makefile文件

# spdx-license-identifier: gpl-2.0
obj-$(config_vgastate)      += vgastate.o
obj-$(config_hdmi)        += hdmi.o

obj-$(config_vt)  += console/
obj-$(config_fb_sti)  += console/
obj-$(config_logo)  += logo/
obj-y   += backlight/

obj-y   += fbdev/

obj-$(config_videomode_helpers) += display_timing.o videomode.o
ifeq ($(config_of),y)
obj-$(config_videomode_helpers) += of_display_timing.o of_videomode.o
endif

3、fbdev默认是被编译的，一般情况下我们只需要看这个目录就行了

config fb_s3c2410
 tristate "s3c2410 lcd framebuffer support"
 depends on fb && arch_s3c24xx
 select fb_cfb_fillrect
 select fb_cfb_copyarea
 select fb_cfb_imageblit
 ---help---
  frame buffer driver for the built-in lcd controller in the samsung
  s3c2410 processor.

  this driver is also available as a module ( = code which can be
  inserted and removed from the running kernel whenever you want). the
  module will be called s3c2410fb. if you want to compile it as a module,
  say m here and read <file:documentation/kbuild/modules.txt>.

  if unsure, say n.
config fb_s3c2410_debug
 bool "s3c2410 lcd debug messages"
 depends on fb_s3c2410
 help
  turn on debugging messages. note that you can set/unset at run time
  through sysfs

4、以s3c2410为例，分析得出其lcd主要依赖的macro是fb_s3c2410,

obj-y  += core/

obj-$(config_fb_s3c2410)  += s3c2410fb.o

5、除了core是默认编译的，我们只需要查看s3c2410fb.c这个文件

static struct platform_driver s3c2410fb_driver = {
 .probe = s3c2410fb_probe,
 .remove = s3c2410fb_remove,
 .suspend = s3c2410fb_suspend,
 .resume = s3c2410fb_resume,
 .driver = {
 .name = "s3c2410-lcd",
 },
};

static struct platform_driver s3c2412fb_driver = {
 .probe = s3c2412fb_probe,
 .remove = s3c2410fb_remove,
 .suspend = s3c2410fb_suspend,
 .resume = s3c2410fb_resume,
 .driver = {
 .name = "s3c2412-lcd",
 },
};

int __init s3c2410fb_init(void)
{
 int ret = platform_driver_register(&s3c2410fb_driver);

 if (ret == 0)
 ret = platform_driver_register(&s3c2412fb_driver);

 return ret;
}

6、不出意外，这又是一个platform设备，接着看看其probe函数做了什么

ret = register_framebuffer(fbinfo);
 if (ret < 0) {
 dev_err(&pdev->dev, "failed to register framebuffer device: %d\n",
  ret);
 goto free_cpufreq;
 }

7、整个代码，最重要的就是这个register动作，当然还要阅读一下是否存在其他的函数接口

static struct fb_ops s3c2410fb_ops = {
 .owner = this_module,
 .fb_check_var = s3c2410fb_check_var,
 .fb_set_par = s3c2410fb_set_par,
 .fb_blank = s3c2410fb_blank,
 .fb_setcolreg = s3c2410fb_setcolreg,
 .fb_fillrect = cfb_fillrect,
 .fb_copyarea = cfb_copyarea,
 .fb_imageblit = cfb_imageblit,
};

8、最后还是老规矩，看看有没有中断需要处理的

ret = request_irq(irq, s3c2410fb_irq, 0, pdev->name, info);

9、后面的话

很多同学把驱动想的很复杂，其实都是一些格式代码。掌握了基本结构，加上芯片手册、硬件协议，一般的驱动都可以在很短的时间内学会，这个不存在问题。尤其是那些在市场上出现了很多年的soc，基本不需要改动就可以直接使用。当然，如果真的发现问题了，我们也要有debug的能力。drivers目录里面的内容很多，但是需要了解和关心的其实不多，努力去做、去解决问题就可以了。

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