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：
在这里插入图片描述

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/fb0
crw-rw----    1 root     root       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.dtsi

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";
};

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_IO
	struct delayed_work deferred_work;
	struct fb_deferred_io *fbdefio;
#endif

	struct 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_TILEBLITTING
	struct fb_tile_ops *tileops;    /* Tile Blitting */
#endif
	char __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_RUNNING	0
#define FBINFO_STATE_SUSPENDED	1
	u32 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 not
	   smem_start/size as smem_start may just be an object
	   allocated 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";
};