嵌入式Linux驱动开发（LCD屏幕专题）（三）

1. 硬件相关的操作

LCD驱动程序的核心就是：

• 分配fb_info
• 设置fb_info
• 注册fb_info
• 硬件相关的设置

硬件相关的设置又可以分为3部分：

• 引脚设置
• 时钟设置
• LCD控制器设置

2. 在设备树里指定LCD参数

	framebuffer-mylcd {compatible = "100ask,lcd_drv";pinctrl-names = "default";pinctrl-0 = <&mylcd_pinctrl>;backlight-gpios = <&gpio1 8 GPIO_ACTIVE_HIGH>;clocks = <&clks IMX6UL_CLK_LCDIF_PIX>,<&clks IMX6UL_CLK_LCDIF_APB>;clock-names = "pix", "axi";display = <&display0>;display0: display {bits-per-pixel = <24>;bus-width = <24>;display-timings {native-mode = <&timing0>;timing0: timing0_1024x768 {clock-frequency = <50000000>;hactive = <1024>;vactive = <600>;hfront-porch = <160>;hback-porch = <140>;hsync-len = <20>;vback-porch = <20>;vfront-porch = <12>;vsync-len = <3>;hsync-active = <0>;vsync-active = <0>;de-active = <1>;pixelclk-active = <0>;};};};            };

3. 编程

3.1 从设备树获得参数

时序参数、引脚极性等信息，都被保存在一个display_timing结构体里：

参考内核文件：

• drivers\video\of_display_timing.c
• drivers\video\fbdev\mxsfb.c

3.2 使用参数配置LCD控制器

根据芯片手册，一个一个设置寄存器：

• Framebuffer地址设置
• Framebuffer中数据格式设置
• LCD时序参数设置
• LCD引脚极性设置

4.上机实验

1. 要做的事情

• 去除内核自带的驱动程序

• 加入我们编写的驱动程序、设备树文件

• 重新编译内核、设备树

• 上机测试：使用编译出来的内核、设备树启动板子

2. 去除内核自带的驱动程序

修改内核文件：drivers/video/fbdev/Makefile，把内核自带驱动程序mxsfb.c对应的那行注释掉，如下：

#obj-$(CONFIG_FB_MXS)             += mxsfb.o

3. 加入新驱动程序、设备树

• 复制驱动程序：

  • 把11_lcd_drv_imx6ull_ok\lcd_drv.c放到内核源码目录drivers/video/fbdev
  • 备份内核自带设备树文件：arch/arm/boot/dts/100ask_imx6ull-14x14.dts
  • 把11_lcd_drv_imx6ull_ok\100ask_imx6ull-14x14.dts放到内核源码目录arch/arm/boot/dts/

• 修改内核文件：

  • 修改：drivers/video/fbdev/Makefile，使用我们提供的lcd_drv.c，如下：

#obj-$(CONFIG_FB_MXS)             += mxsfb.o
obj-$(CONFIG_FB_MXS)             += lcd_drv.o

4. 重新编译内核、设备树

以下命令在Ubuntu中执行。

• 设置工具链

  export ARCH=armexport CROSS_COMPILE=arm-linux-gnueabihf-export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/gcc-linaro-6.2.1-2016.11-x86_64_arm-linux-gnueabihf/bin

• 配置、编译

  book@100ask:~/100ask_imx6ull-sdk$ cd Linux-4.9.88book@100ask:~/100ask_imx6ull-sdk/Linux-4.9.88$ make 100ask_imx6ull_defconfig   book@100ask:~/100ask_imx6ull-sdk/Linux-4.9.88$ make zImage book@100ask:~/100ask_imx6ull-sdk/Linux-4.9.88$ make dtbs

• 得到

  • 内核：arch/arm/boot/zImage
  • 设备树文件：arch/arm/boot/dts/100ask_imx6ull-14x14.dtb

• 复制到NFS目录：

  $ cp arch/arm/boot/zImage ~/nfs_rootfs/$ cp arch/arm/boot/dts/100ask_imx6ull-14x14.dtb ~/nfs_rootfs/

5. 上机测试

以下命令在开发板中执行。

• 挂载NFS

  • vmware使用NAT(假设windowsIP为192.168.1.100)

    [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
    192.168.1.100:/home/book/nfs_rootfs /mnt
    

  • vmware使用桥接，或者不使用vmware而是直接使用服务器：假设Ubuntu IP为192.168.1.137

    [root@100ask:~]#  mount -t nfs -o nolock,vers=3 192.168.1.137:/home/book/nfs_rootfs /mnt
    

• 更新单板文件

  [root@100ask:~]# cp /mnt/zImage /boot[root@100ask:~]# cp /mnt/100ask_imx6ull-14x14.dtb /boot[root@100ask:~]# sync

• 重启开发板观察现象

  • 如果可以看到企鹅LOGO，就表示正常
  • 如果在终端中可以查看到存在/dev/fb0节点，也表示正常

• 解决BUG

  • 现象：LCD上没有企鹅LOGO，在终端中执行ls -l /dev/fb0发现没有设备节点

  • 观察内核启动信息，看到：

    [    0.619880] imx6ul-pinctrl 20e0000.iomuxc: pin MX6UL_PAD_GPIO1_IO08 already requested by 2080000.pwm; cannot claim for 21c8000.framebuffer-mylcd
    [    0.619920] imx6ul-pinctrl 20e0000.iomuxc: pin-31 (21c8000.framebuffer-mylcd) status -22
    [    0.619954] imx6ul-pinctrl 20e0000.iomuxc: could not request pin 31 (MX6UL_PAD_GPIO1_IO08) from group mylcd_pingrp  on device 20e0000.iomuxc
    [    0.619985] mylcd 21c8000.framebuffer-mylcd: Error applying setting, reverse things back
    [    0.620070] mylcd: probe of 21c8000.framebuffer-mylcd failed with error -22
    

  • 原因：引脚冲突

    • 设备树中pwm节点、framebuffer-mylcd节点，都使用到的同一个引脚：PAD_GPIO1_IO08

  • 解决方法：修改arch/arm/boot/dts/100ask_imx6ull-14x14.dts，禁止pwm节点，如下：
    

6、代码

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/err.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 <linux/io.h>
#include <video/display_timing.h>
#include <video/of_display_timing.h>
#include <linux/gpio/consumer.h>
#include <asm/div64.h>
#include <asm/mach/map.h>struct imx6ull_lcdif {volatile unsigned int CTRL;                              volatile unsigned int CTRL_SET;                        volatile unsigned int CTRL_CLR;                         volatile unsigned int CTRL_TOG;                         volatile unsigned int CTRL1;                             volatile unsigned int CTRL1_SET;                         volatile unsigned int CTRL1_CLR;                       volatile unsigned int CTRL1_TOG;                       volatile unsigned int CTRL2;                            volatile unsigned int CTRL2_SET;                       volatile unsigned int CTRL2_CLR;                        volatile unsigned int CTRL2_TOG;                        volatile unsigned int TRANSFER_COUNT;   unsigned char RESERVED_0[12];volatile unsigned int CUR_BUF;                          unsigned char RESERVED_1[12];volatile unsigned int NEXT_BUF;                        unsigned char RESERVED_2[12];volatile unsigned int TIMING;                          unsigned char RESERVED_3[12];volatile unsigned int VDCTRL0;                         volatile unsigned int VDCTRL0_SET;                      volatile unsigned int VDCTRL0_CLR;                     volatile unsigned int VDCTRL0_TOG;                     volatile unsigned int VDCTRL1;                          unsigned char RESERVED_4[12];volatile unsigned int VDCTRL2;                          unsigned char RESERVED_5[12];volatile unsigned int VDCTRL3;                          unsigned char RESERVED_6[12];volatile unsigned int VDCTRL4;                           unsigned char RESERVED_7[12];volatile unsigned int DVICTRL0;    unsigned char RESERVED_8[12];volatile unsigned int DVICTRL1;                         unsigned char RESERVED_9[12];volatile unsigned int DVICTRL2;                        unsigned char RESERVED_10[12];volatile unsigned int DVICTRL3;                        unsigned char RESERVED_11[12];volatile unsigned int DVICTRL4;                          unsigned char RESERVED_12[12];volatile unsigned int CSC_COEFF0;  unsigned char RESERVED_13[12];volatile unsigned int CSC_COEFF1;                        unsigned char RESERVED_14[12];volatile unsigned int CSC_COEFF2;                        unsigned char RESERVED_15[12];volatile unsigned int CSC_COEFF3;                        unsigned char RESERVED_16[12];volatile unsigned int CSC_COEFF4;   unsigned char RESERVED_17[12];volatile unsigned int CSC_OFFSET;  unsigned char RESERVED_18[12];volatile unsigned int CSC_LIMIT;  unsigned char RESERVED_19[12];volatile unsigned int DATA;                              unsigned char RESERVED_20[12];volatile unsigned int BM_ERROR_STAT;                     unsigned char RESERVED_21[12];volatile unsigned int CRC_STAT;                        unsigned char RESERVED_22[12];volatile  unsigned int STAT;                             unsigned char RESERVED_23[76];volatile unsigned int THRES;                             unsigned char RESERVED_24[12];volatile unsigned int AS_CTRL;                           unsigned char RESERVED_25[12];volatile unsigned int AS_BUF;                            unsigned char RESERVED_26[12];volatile unsigned int AS_NEXT_BUF;                     unsigned char RESERVED_27[12];volatile unsigned int AS_CLRKEYLOW;                    unsigned char RESERVED_28[12];volatile unsigned int AS_CLRKEYHIGH;                   unsigned char RESERVED_29[12];volatile unsigned int SYNC_DELAY;                      
} ;struct lcd_regs {volatile unsigned int fb_base_phys;volatile unsigned int fb_xres;volatile unsigned int fb_yres;volatile unsigned int fb_bpp;	
};static struct lcd_regs *mylcd_regs;
static struct fb_info *myfb_info;
static unsigned int pseudo_palette[16];static struct gpio_desc *bl_gpio;
static struct clk* clk_pix;
static struct clk* clk_axi;static void lcd_controller_enable(struct imx6ull_lcdif *lcdif)
{lcdif->CTRL |= (1<<0);
}static int lcd_controller_init(struct imx6ull_lcdif *lcdif, struct display_timing *dt, int lcd_bpp, int fb_bpp, unsigned int fb_phy)
{int lcd_data_bus_width;int fb_width;int vsync_pol = 0;int hsync_pol = 0;int de_pol = 0;int clk_pol = 0;if (dt->flags & DISPLAY_FLAGS_HSYNC_HIGH)hsync_pol = 1;if (dt->flags & DISPLAY_FLAGS_VSYNC_HIGH)vsync_pol = 1;if (dt->flags & DISPLAY_FLAGS_DE_HIGH)de_pol = 1;if (dt->flags & DISPLAY_FLAGS_PIXDATA_POSEDGE)clk_pol = 1;if (lcd_bpp == 24)lcd_data_bus_width = 0x3;else if (lcd_bpp == 18)lcd_data_bus_width = 0x2;else if (lcd_bpp == 8)lcd_data_bus_width = 0x1;else if (lcd_bpp == 16)lcd_data_bus_width = 0x0;elsereturn -1;if (fb_bpp == 24 || fb_bpp == 32)fb_width = 0x3;else if (fb_bpp == 18)fb_width = 0x2;else if (fb_bpp == 8)fb_width = 0x1;else if (fb_bpp == 16)fb_width = 0x0;elsereturn -1;/* * 初始化LCD控制器的CTRL寄存器* [19]       :  1      : DOTCLK和DVI modes需要设置为1 * [17]       :  1      : 设置为1工作在DOTCLK模式* [15:14]    : 00      : 输入数据不交换（小端模式）默认就为0，不需设置* [13:12]    : 00      : CSC数据不交换（小端模式）默认就为0，不需设置* [11:10]    : 11		: 数据总线为24bit* [9:8]    根据显示屏资源文件bpp来设置：8位0x1 ， 16位0x0 ，24位0x3* [5]        :  1      : 设置elcdif工作在主机模式* [1]        :  0      : 24位数据均是有效数据，默认就为0，不需设置*/	lcdif->CTRL = (0<<30) | (0<<29) | (0<<28) | (1<<19) | (1<<17) | (lcd_data_bus_width << 10) |\(fb_width << 8) | (1<<5);/** 设置ELCDIF的寄存器CTRL1* 根据bpp设置，bpp为24或32才设置* [19:16]  : 111  :表示ARGB传输格式模式下，传输24位无压缩数据，A通道不用传输）*/	  if(fb_bpp == 24 || fb_bpp == 32){	  lcdif->CTRL1 &= ~(0xf << 16); lcdif->CTRL1 |=  (0x7 << 16); }elselcdif->CTRL1 |= (0xf << 16); /** 设置ELCDIF的寄存器TRANSFER_COUNT寄存器* [31:16]  : 垂直方向上的像素个数  * [15:0]   : 水平方向上的像素个数*/lcdif->TRANSFER_COUNT  = (dt->vactive.typ << 16) | (dt->hactive.typ << 0);/** 设置ELCDIF的VDCTRL0寄存器* [29] 0 : VSYNC输出  ，默认为0，无需设置* [28] 1 : 在DOTCLK模式下，设置1硬件会产生使能ENABLE输出* [27] 0 : VSYNC低电平有效	,根据屏幕配置文件将其设置为0* [26] 0 : HSYNC低电平有效 , 根据屏幕配置文件将其设置为0* [25] 1 : DOTCLK下降沿有效 ，根据屏幕配置文件将其设置为1* [24] 1 : ENABLE信号高电平有效，根据屏幕配置文件将其设置为1* [21] 1 : 帧同步周期单位，DOTCLK mode设置为1* [20] 1 : 帧同步脉冲宽度单位，DOTCLK mode设置为1* [17:0] :  vysnc脉冲宽度 */lcdif->VDCTRL0 = (1 << 28)|( vsync_pol << 27)\|( hsync_pol << 26)\|( clk_pol << 25)\|( de_pol << 24)\|(1 << 21)|(1 << 20)|( dt->vsync_len.typ << 0);/** 设置ELCDIF的VDCTRL1寄存器* 设置垂直方向的总周期:上黑框tvb+垂直同步脉冲tvp+垂直有效高度yres+下黑框tvf*/	  lcdif->VDCTRL1 = dt->vback_porch.typ + dt->vsync_len.typ + dt->vactive.typ + dt->vfront_porch.typ;  /** 设置ELCDIF的VDCTRL2寄存器* [18:31]  : 水平同步信号脉冲宽度* [17: 0]   : 水平方向总周期* 设置水平方向的总周期:左黑框thb+水平同步脉冲thp+水平有效高度xres+右黑框thf*/ lcdif->VDCTRL2 = (dt->hsync_len.typ << 18) | (dt->hback_porch.typ + dt->hsync_len.typ + dt->hactive.typ + dt->hfront_porch.typ);/** 设置ELCDIF的VDCTRL3寄存器* [27:16] ：水平方向上的等待时钟数 =thb + thp* [15:0]  : 垂直方向上的等待时钟数 = tvb + tvp*/ lcdif->VDCTRL3 = ((dt->hback_porch.typ + dt->hsync_len.typ) << 16) | (dt->vback_porch.typ + dt->vsync_len.typ);/** 设置ELCDIF的VDCTRL4寄存器* [18]	   使用VSHYNC、HSYNC、DOTCLK模式此为置1* [17:0]  : 水平方向的宽度*/ lcdif->VDCTRL4 = (1<<18) | (dt->hactive.typ);/** 设置ELCDIF的CUR_BUF和NEXT_BUF寄存器* CUR_BUF	 :	当前显存地址* NEXT_BUF :	下一帧显存地址* 方便运算，都设置为同一个显存地址*/ lcdif->CUR_BUF  =  fb_phy;lcdif->NEXT_BUF =  fb_phy;return 0;
}/* 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 mylcd_setcolreg(unsigned regno,unsigned red, unsigned green, unsigned blue,unsigned transp, struct fb_info *info)
{unsigned int val;/* dprintk("setcol: regno=%d, rgb=%d,%d,%d\n",regno, red, green, blue); */switch (info->fix.visual) {case FB_VISUAL_TRUECOLOR:/* true-colour, use pseudo-palette */if (regno < 16) {u32 *pal = info->pseudo_palette;val  = chan_to_field(red,   &info->var.red);val |= chan_to_field(green, &info->var.green);val |= chan_to_field(blue,  &info->var.blue);pal[regno] = val;}break;default:return 1;	/* unknown type */}return 0;
}static struct fb_ops myfb_ops = {.owner		= THIS_MODULE,.fb_setcolreg	= mylcd_setcolreg,.fb_fillrect	= cfb_fillrect,.fb_copyarea	= cfb_copyarea,.fb_imageblit	= cfb_imageblit,
};static int mylcd_probe(struct platform_device *pdev)
{struct device_node *display_np;dma_addr_t phy_addr;int ret;int width;int bits_per_pixel;struct display_timings *timings = NULL;struct display_timing *dt = NULL;struct imx6ull_lcdif *lcdif;struct resource *res;display_np = of_parse_phandle(pdev->dev.of_node, "display", 0);/* get common info */ret = of_property_read_u32(display_np, "bus-width", &width);ret = of_property_read_u32(display_np, "bits-per-pixel",&bits_per_pixel);/* get timming */timings = of_get_display_timings(display_np);dt = timings->timings[timings->native_mode];/* get gpio from device tree */bl_gpio = gpiod_get(&pdev->dev, "backlight", 0);/* config bl_gpio as output */gpiod_direction_output(bl_gpio, 1);/* set val: gpiod_set_value(bl_gpio, status); *//* get clk from device tree */clk_pix = devm_clk_get(&pdev->dev, "pix");clk_axi = devm_clk_get(&pdev->dev, "axi");/* set clk rate */clk_set_rate(clk_pix, dt->pixelclock.typ);/* enable clk */clk_prepare_enable(clk_pix);clk_prepare_enable(clk_axi);/* 1.1 分配fb_info */myfb_info = framebuffer_alloc(0, NULL);/* 1.2 设置fb_info *//* a. var : LCD分辨率、颜色格式 */myfb_info->var.xres_virtual = myfb_info->var.xres = dt->hactive.typ;myfb_info->var.yres_virtual = myfb_info->var.yres = dt->vactive.typ;myfb_info->var.bits_per_pixel = 16;  /* rgb565 */myfb_info->var.red.offset = 11;myfb_info->var.red.length = 5;myfb_info->var.green.offset = 5;myfb_info->var.green.length = 6;myfb_info->var.blue.offset = 0;myfb_info->var.blue.length = 5;/* b. fix */strcpy(myfb_info->fix.id, "100ask_lcd");myfb_info->fix.smem_len = myfb_info->var.xres * myfb_info->var.yres * myfb_info->var.bits_per_pixel / 8;if (myfb_info->var.bits_per_pixel == 24)myfb_info->fix.smem_len = myfb_info->var.xres * myfb_info->var.yres * 4;/* fb的虚拟地址 */myfb_info->screen_base = dma_alloc_wc(NULL, myfb_info->fix.smem_len, &phy_addr,GFP_KERNEL);myfb_info->fix.smem_start = phy_addr;  /* fb的物理地址 */myfb_info->fix.type = FB_TYPE_PACKED_PIXELS;myfb_info->fix.visual = FB_VISUAL_TRUECOLOR;myfb_info->fix.line_length = myfb_info->var.xres * myfb_info->var.bits_per_pixel / 8;if (myfb_info->var.bits_per_pixel == 24)myfb_info->fix.line_length = myfb_info->var.xres * 4;/* c. fbops */myfb_info->fbops = &myfb_ops;myfb_info->pseudo_palette = pseudo_palette;/* 1.3 注册fb_info */register_framebuffer(myfb_info);/* 1.4 硬件操作 *///lcdif = ioremap(0x021C8000, sizeof(*lcdif));res = platform_get_resource(pdev, IORESOURCE_MEM, 0);lcdif = devm_ioremap_resource(&pdev->dev, res);lcd_controller_init(lcdif, dt, bits_per_pixel, 16, phy_addr);lcd_controller_enable(lcdif);gpiod_set_value(bl_gpio, 1); return 0;
}static int mylcd_remove(struct platform_device *pdev)
{/* 反过来操作 *//* 2.1 反注册fb_info */unregister_framebuffer(myfb_info);/* 2.2 释放fb_info */framebuffer_release(myfb_info);iounmap(mylcd_regs);return 0;
}static const struct of_device_id mylcd_of_match[] = {{ .compatible = "100ask,lcd_drv", },{ },
};
MODULE_DEVICE_TABLE(of, simplefb_of_match);static struct platform_driver mylcd_driver = {.driver = {.name = "mylcd",.of_match_table = mylcd_of_match,},.probe = mylcd_probe,.remove = mylcd_remove,
};static int __init lcd_drv_init(void)
{int ret;ret = platform_driver_register(&mylcd_driver);if (ret)return ret;return 0;
}/* 2. 出口 */
static void __exit lcd_drv_exit(void)
{platform_driver_unregister(&mylcd_driver);
}module_init(lcd_drv_init);
module_exit(lcd_drv_exit);
MODULE_LICENSE("GPL");