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linux驱动摸索

内核版本：linux-2.6.32.2

开发板：mini2440

TFT屏：统宝3.5寸屏

LCD内核框架：

内核自带的LCD驱动程序：drivers/video/S3c2410fb.c
这个驱动程序通过提供最底层的操作来被核心层调用，这个核心层提供了应用程序所需 open/close，read/write 其中drivers/video/fbmem.c提供了对LCD的所有抽象操作。

LCD硬件原理简介：

• VD3-VD23: video data引脚，lcd控制器发的数据在这几根线上
• VLINE: 能发出HSYNC信号，用于切换到下一行扫描
• VFRAME: 能发出VSYNC信号，用于返回到最开始行的扫描
• VCLK：控制器发给lcd的时钟引脚，根据lcd手册设置
• VM／VDEN: video data 使能引脚

LCD驱动编写步骤

1.分配一个fb_info结构

mini2440fb = framebuffer_alloc(0, NULL);

注意：每一个lcd驱动程序都要分配一个fb_info结构体,framebuffer_alloc的用法可以参考其他lcd驱动，第一个参数0表示只需要分配本结构体的长度，
第二个NULL，表示无device结构，返回值为fb_info结构体。

2.设置fb_info的fix，val等相关参数,例如：

	mini2440fb->fix.smem_len = MINI2440_LCD_WIDTH*MINI2440_LCD_LENGTH*MINI2440_LCD_DEEPTH/8;        /* Length of frame buffer mem */mini2440fb->fix.type = FB_TYPE_PACKED_PIXELS;	/* see FB_TYPE_**/mini2440fb->fix.visual = FB_VISUAL_TRUECOLOR;	/* see FB_VISUAL_**/ mini2440fb->fix.line_length = MINI2440_LCD_WIDTH*MINI2440_LCD_DEEPTH/8;		/* length of a line in bytes    */

注意：在设置操作函数中这个操作函数是必须的，具体可参考 S3c2410fb.c中的相关配置，还有在mini2440中LCD位宽是24,但是2440里会分配4字节即32位(浪费1字节)即设置 MINI2440_LCD_DEEPTH 为32.

3.硬件相关的操作：

参考s3c2440手册和lcd手册，配置相关参数，在mini2440开发板中。背光控制引脚是GPG4.

4.注册

register_framebuffer(mini2440fb);

mini2440 LCD驱动程序，源码如下：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/fb.h>
#include <linux/init.h>
#include <linux/dma-mapping.h>
#include <linux/interrupt.h>
#include <linux/platform_device.h>
#include <linux/clk.h>
#include <linux/cpufreq.h>#include <asm/io.h>
#include <asm/div64.h>#include <asm/mach/map.h>
#include <mach/regs-lcd.h>
#include <mach/regs-gpio.h>
#include <mach/fb.h>#define MINI2440_LCD_WIDTH  240
#define MINI2440_LCD_LENGTH 320
#define MINI2440_LCD_DEEPTH 32struct lcd_regs {unsigned long	lcdcon1;unsigned long	lcdcon2;unsigned long	lcdcon3;unsigned long	lcdcon4;unsigned long	lcdcon5;unsigned long	lcdsaddr1;unsigned long	lcdsaddr2;unsigned long	lcdsaddr3;unsigned long	redlut;unsigned long	greenlut;unsigned long	bluelut;unsigned long	reserved[9];unsigned long	dithmode;unsigned long	tpal;unsigned long	lcdintpnd;unsigned long	lcdsrcpnd;unsigned long	lcdintmsk;unsigned long	lpcsel;
};static volatile unsigned long *gpccon;
static volatile unsigned long *gpdcon;
static volatile unsigned long *gpgcon;
static volatile unsigned long *gpgdat;
static u32 pseudo_palette[16];static struct fb_info *mini2440fb;
static volatile struct lcd_regs *s3c_lcd_regs;/* from pxafb.c */
static inline unsigned int chan_to_field(unsigned int chan,struct fb_bitfield *bf)
{chan &= 0xffff;chan >>= 16 - bf->length;return chan << bf->offset;
}static int mini2440fb_setcolreg(unsigned regno,unsigned red, unsigned green, unsigned blue,unsigned transp, struct fb_info *info)
{unsigned int val;if (regno > 16)return 1;/* 用red,green,blue三原色构造出val */val  = chan_to_field(red,	&info->var.red);val |= chan_to_field(green, &info->var.green);val |= chan_to_field(blue,	&info->var.blue);//((u32 *)(info->pseudo_palette))[regno] = val;pseudo_palette[regno] = val;return 0;}static struct fb_ops mini2440fb_ops = {.owner		= THIS_MODULE,.fb_setcolreg	= mini2440fb_setcolreg,.fb_fillrect	= cfb_fillrect,.fb_copyarea	= cfb_copyarea,.fb_imageblit	= cfb_imageblit,
};static int mini2440_tft_t35_init(void)
{/*1.分配一个fb_info结构体*/mini2440fb = framebuffer_alloc(0, NULL);  //不需要额外的私有空间，设为0if (!mini2440fb){printk("framebuffer_alloc filed\n");return -ENOMEM;}/*2.设置*//*set fix param*/strcpy(mini2440fb->fix.id, "mytft");mini2440fb->fix.smem_len = MINI2440_LCD_WIDTH*MINI2440_LCD_LENGTH*MINI2440_LCD_DEEPTH/8;        /* Length of frame buffer mem */mini2440fb->fix.type = FB_TYPE_PACKED_PIXELS;	/* see FB_TYPE_**/mini2440fb->fix.visual = FB_VISUAL_TRUECOLOR;	/* see FB_VISUAL_**/ mini2440fb->fix.line_length = MINI2440_LCD_WIDTH*MINI2440_LCD_DEEPTH/8;		/* length of a line in bytes    *//*set var param*/mini2440fb->var.xres = MINI2440_LCD_WIDTH;			/* visible resolution*/mini2440fb->var.yres = MINI2440_LCD_LENGTH;mini2440fb->var.xres_virtual = MINI2440_LCD_WIDTH;		/* virtual resolution*/mini2440fb->var.yres_virtual = MINI2440_LCD_LENGTH;mini2440fb->var.bits_per_pixel = MINI2440_LCD_DEEPTH;	/* guess what	*/mini2440fb->var.red.offset = 16;		/* bitfield in fb mem if true color, */mini2440fb->var.red.length = 8;mini2440fb->var.green.offset = 8;		mini2440fb->var.green.length = 8 ;mini2440fb->var.blue.offset = 0;		mini2440fb->var.blue.length = 8;	mini2440fb->var.activate = FB_ACTIVATE_NOW;			/* see FB_ACTIVATE_**/mini2440fb->fbops = &mini2440fb_ops;mini2440fb->pseudo_palette = pseudo_palette;mini2440fb->screen_size = MINI2440_LCD_WIDTH*MINI2440_LCD_LENGTH*MINI2440_LCD_DEEPTH/8;/*3.硬件相关的配置*/gpccon = ioremap(0x56000020,4);gpdcon = ioremap(0x56000030,4);gpgcon = ioremap(0x56000060,4);gpgdat = gpgcon + 1;/*3.1将GPIOC,GPIOD配成VD模式*/*gpccon = 0xaaaaaaaa;*gpdcon = 0xaaaaaaaa;/*3.2配置背光GPIOG4,低电平，关闭*/*gpgcon &= ~(3<<8);*gpgcon |=  (1<<8);*gpgdat &= ~(1<<4);//*gpgcon |= (3<<8);/*3.3配置lcd相关寄存器*/s3c_lcd_regs = ioremap(0X4D000000,sizeof(struct lcd_regs));/*  LCDCON1 : *  CLKVAL [17:8]:VCLK = HCLK / [(CLKVAL+1) x 2] HCLK=100Mhz,VCLK=6400000*                 CLKVAL = 7*  PNRMODE [6:5]:11 = TFT LCD panel*  BPPMODE [4:1]:1100 = 16 bpp for TFT*  ENVID [0]:0 = Disable the video output and the LCD control signal.*            1 = Enable the video output and the LCD control signal.*/s3c_lcd_regs->lcdcon1 = (7<<8)|(3<<5)|(0x0d<<1);/*  LCDCON2 : *  VBPD [31:24]:VBPD+1 = 4*  LINEVAL [23:14] : LINEVAL+1=320*  VFPD [13:6]:VFPD+1=2*  VSPW [5:0]:VSPW+1 =2*/	s3c_lcd_regs->lcdcon2 = (3<<24)|(319<<14)|(1<<6)|(1<<0);/*  LCDCON3 : *  HBPD (TFT) [25:19]: HBPD+1=30*  HOZVAL [18:8] : HOZVAL+1=240*  HFPD (TFT) [7:0]:HFPD+1=10*/		s3c_lcd_regs->lcdcon3 = (29<<19)|(239<<8)|(9<<0);/*	LCDCON4 : *  HSPW(TFT) [7:0]:HSPW+1=10*/ s3c_lcd_regs->lcdcon4 = 0;/*  LCDCON5 : *  FRM565 [11]: 1 = 5:6:5 Format*  INVVCLK [10]:1 = The video data is fetched at VCLK rising edge*  INVVLINE [9] 1 = Inverted*  INVVFRAME [8] 1 = Inverted*  INVVDEN [6]  0 = normal*  PWREN [3]: 0 = Disable PWREN signal 1 = Enable PWREN signal*  BSWP [1]:  0   见2440手册 413页HWSWP [0]: 0*/		s3c_lcd_regs->lcdcon5 = (1<<10) | (1<<9) | (1<<8) | (0<<12) | (0<<1) | (0<<0);/*分配显存(framebuffer), 并把地址告诉LCD控制器*/mini2440fb->screen_base =dma_alloc_writecombine(NULL,mini2440fb->fix.smem_len,\&mini2440fb->fix.smem_start,GFP_KERNEL);s3c_lcd_regs->lcdsaddr1 = (mini2440fb->fix.smem_start>>1)&(~(3<<30));s3c_lcd_regs->lcdsaddr2 = ((mini2440fb->fix.smem_start+mini2440fb->fix.smem_len)>>1)&\(0x1fffff);s3c_lcd_regs->lcdsaddr3 =(240*MINI2440_LCD_DEEPTH/16);  /* 一行的长度(单位: 2字节) */	/*使能LCD*/s3c_lcd_regs->lcdcon1 |= 1;s3c_lcd_regs->lcdcon5 |=(1<<3);*gpgdat |= (1<<4);/*注册*/register_framebuffer(mini2440fb);return 0;
}static void mini2440_tft_t35_exit(void)
{unregister_framebuffer(mini2440fb);s3c_lcd_regs->lcdcon1 &= ~1;s3c_lcd_regs->lcdcon5 &=~(1<<3);*gpgdat &= ~(1<<4);dma_free_writecombine(NULL, mini2440fb->fix.smem_len, mini2440fb->screen_base,\mini2440fb->fix.smem_start);iounmap(gpccon);iounmap(gpdcon);iounmap(gpgcon);iounmap(s3c_lcd_regs);framebuffer_release(mini2440fb);
}/* 这两行指定驱动程序的初始化函数和卸载函数 */
module_init(mini2440_tft_t35_init);
module_exit(mini2440_tft_t35_exit);/* 描述驱动程序的一些信息*/MODULE_LICENSE("GPL");

测试：

1. make menuconfig去掉原来的驱动程序，mini2440开发板提供的内核时，需要把相关的LCD驱动去掉。
-> Device Drivers
-> Graphics support
<M> S3C2410 LCD framebuffer support

2. make uImage
make modules

3. 使用新的uImage启动开发板:
4.
insmod cfbcopyarea.ko
insmod cfbfillrect.ko
insmod cfbimgblt.ko
insmod tft.ko

echo hello > /dev/tty1 // 可以在LCD上看见hello