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i.MX 6ULL 驱动开发十九：RGBLCD

时间：2020-07-04 19:07:13

一、RGBLCD 硬件原理

【正点原子MP157连载】第十八章 RGB LCD彩条显示实验-摘自【正点原子】STM32MP1嵌入式Linux驱动开发指南V1.7_正点原子的博客-CSDN博客

ATK7016时序参数：

二、eLCDIF 接口

eLCDIF是I.MX6U自带的液晶屏幕接口，用于连接RGB LCD接口的屏幕。

三、Linux 下 LCD 驱动分析

1、LCD 操作流程

1、初始化I.MX6U的eLCDIF控制器，重点是LCD屏幕宽(width)、高(height)、hspw、hbp、hfp、vspw、vbp和vfp等信息。

2、初始化LCD像素时钟。

3、设置RGBLCD显存。

4、应用程序直接通过操作显存来操作LCD，实现在LCD上显示字符、图片等信息。

2、Framebuffer 设备

Linux内核中使用Framebuffer提供统一的标准接口显示设备。Framebuffer翻译过来就是帧缓冲，简称fb。fb是一种机制，将系统中所有跟显示有关的硬件以及软件集合起来，虚拟出一个fb设备，当我们编写好LCD驱动以后会生成一个名为/dev/fbX(X=0~n)的设备，应用程序通过访问/dev/fbX这个设备就可以访问LCD。

NXP官方的Linux内核默认已经开启了LCD驱动，因此我们是可以看到/dev/fb0这样一个设备，如下所示：

# ls -l /dev/fb0crw-rw---- 1 rootroot 29, 0 Jan 1 00:00 /dev/fb0#

/dev/fb0就是LCD对应的设备文件，/dev/fb0是个字符设备，fb的file_operations操作集定义在drivers/video/fbdev/core/fbmem.c文件中。

3、驱动分析

1、通过设备树确定驱动文件

设备树信息如下：

// 文件路径：linux-imx-4.1.15\arch\arm\boot\dts\imx6ull.dtsilcdif: lcdif@021c8000 {compatible = "fsl,imx6ul-lcdif", "fsl,imx28-lcdif";reg = <0x021c8000 0x4000>;interrupts = <GIC_SPI 5 IRQ_TYPE_LEVEL_HIGH>;clocks = <&clks IMX6UL_CLK_LCDIF_PIX>,<&clks IMX6UL_CLK_LCDIF_APB>,<&clks IMX6UL_CLK_DUMMY>;clock-names = "pix", "axi", "disp_axi";status = "disabled";};

通过fsl,imx6ul-lcdif或fsl,imx28-lcdif查找驱动文件，驱动文件路径：linux-imx-4.1.15\drivers\video\fbdev\mxsfb.c。

驱动分析待完成……。

四、重要结构体

1、fb_info

struct fb_info {atomic_t count;int node;int flags;struct mutex lock;/* Lock for open/release/ioctl funcs */struct mutex mm_lock;/* Lock for fb_mmap and smem_* fields */struct fb_var_screeninfo var;/* Current var */struct fb_fix_screeninfo fix;/* Current fix */struct fb_monspecs monspecs;/* Current Monitor specs */struct work_struct queue;/* Framebuffer event queue */struct fb_pixmap pixmap;/* Image hardware mapper */struct fb_pixmap sprite;/* Cursor hardware mapper */struct fb_cmap cmap;/* Current cmap */struct list_head modelist;/* mode list */struct fb_videomode *mode;/* current mode */#ifdef CONFIG_FB_BACKLIGHT/* assigned backlight device *//* set before framebuffer registration, remove after unregister */struct backlight_device *bl_dev;/* Backlight level curve */struct mutex bl_curve_mutex;u8 bl_curve[FB_BACKLIGHT_LEVELS];#endif#ifdef CONFIG_FB_DEFERRED_IOstruct delayed_work deferred_work;struct fb_deferred_io *fbdefio;#endifstruct fb_ops *fbops;struct device *device;/* This is the parent */struct device *dev;/* This is this fb device */int class_flag;/* private sysfs flags */#ifdef CONFIG_FB_TILEBLITTINGstruct fb_tile_ops *tileops; /* Tile Blitting */#endifchar __iomem *screen_base;/* Virtual address */unsigned long screen_size;/* Amount of ioremapped VRAM or 0 */ void *pseudo_palette;/* Fake palette of 16 colors */ #define FBINFO_STATE_RUNNING0#define FBINFO_STATE_SUSPENDED1u32 state;/* Hardware state i.e suspend */void *fbcon_par;/* fbcon use-only private area *//* From here on everything is device dependent */void *par;/* we need the PCI or similar aperture base/size notsmem_start/size as smem_start may just be an objectallocated inside the aperture so may not actually overlap */struct apertures_struct {unsigned int count;struct aperture {resource_size_t base;resource_size_t size;} ranges[0];} *apertures;bool skip_vt_switch; /* no VT switch on suspend/resume required */};

2、mxsfb_info

struct mxsfb_info {struct fb_info *fb_info;struct platform_device *pdev;struct clk *clk_pix;struct clk *clk_axi;struct clk *clk_disp_axi;bool clk_pix_enabled;bool clk_axi_enabled;bool clk_disp_axi_enabled;void __iomem *base;/* registers */u32 sync;/* record display timing polarities */unsigned allocated_size;int enabled;unsigned ld_intf_width;unsigned dotclk_delay;const struct mxsfb_devdata *devdata;struct regulator *reg_lcd;bool wait4vsync;struct completion vsync_complete;struct completion flip_complete;int cur_blank;int restore_blank;char disp_dev[32];struct mxc_dispdrv_handle *dispdrv;int id;struct fb_var_screeninfo var;};

五、设备树添加

1、设备树添加说明

Linux 驱动开发六十二：《mxsfb.txt》翻译_lqonlylove的博客-CSDN博客

Linux 驱动开发六十三：《display-timing.txt》翻译_lqonlylove的博客-CSDN博客

2、添加设备树

在lcdif节点中追加或修改LCD时序相关参数，如题内容如下：

lcdif: lcdif@021c8000 {compatible = "fsl,imx6ul-lcdif", "fsl,imx28-lcdif";reg = <0x021c8000 0x4000>;interrupts = <GIC_SPI 5 IRQ_TYPE_LEVEL_HIGH>;clocks = <&clks IMX6UL_CLK_LCDIF_PIX>,<&clks IMX6UL_CLK_LCDIF_APB>,<&clks IMX6UL_CLK_DUMMY>;clock-names = "pix", "axi", "disp_axi";status = "disabled";};&lcdif {pinctrl-names = "default";pinctrl-0 = <&pinctrl_lcdif_dat&pinctrl_lcdif_ctrl>;display = <&display0>;status = "okay";/* 7寸1024*600 */display0: display {bits-per-pixel = <32>;// RGB值（RGB888/666）bus-width = <24>;// 数据线数量display-timings {native-mode = <&timing0>;timing0: timing0 {clock-frequency = <51200000>;// 时钟配置hactive = <1024>;// 水平像素点vactive = <600>;// 垂直像素点hfront-porch = <160>;// HFP 配置hback-porch = <140>;// HBP 配置hsync-len = <20>;// HSPW 配置vback-porch = <20>;// VBP 配置vfront-porch = <12>;// VFP 配置vsync-len = <3>;// VSPW 配置hsync-active = <0>;// HSYNC 信号有效电平vsync-active = <0>;// VSYNC 信号有效电平de-active = <1>;// DE 信号有效电平pixelclk-active = <0>;// 数据更新和数据采样有效电平};};};};

六、LCD 背光配置

1、确定LCD背光使用的 PIN 引脚

通过原理图确定背光使用的PIN引脚。LCD使用引脚为BLT_PWM（GPIO1_IO08）。LCD背光使用PWM驱动。

2、设备树配置

pinctrl_pwm1: pwm1grp {fsl,pins = <MX6UL_PAD_GPIO1_IO08__PWM1_OUT 0x110b0>;};pwm1: pwm@02080000 {compatible = "fsl,imx6ul-pwm", "fsl,imx27-pwm";reg = <0x02080000 0x4000>;interrupts = <GIC_SPI 83 IRQ_TYPE_LEVEL_HIGH>;clocks = <&clks IMX6UL_CLK_PWM1>,<&clks IMX6UL_CLK_PWM1>;clock-names = "ipg", "per";#pwm-cells = <2>;};&pwm1 {pinctrl-names = "default";pinctrl-0 = <&pinctrl_pwm1>;status = "okay";};backlight {compatible = "pwm-backlight";pwms = <&pwm1 0 5000000>;brightness-levels = <0 4 8 16 32 64 128 255>;default-brightness-level = <7>;status = "okay";};