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: %dn”, 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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