linux驱动编写（lcd驱动）

    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。