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13_编程/_配置时钟/_基于IMX6ULL

编程/_配置时钟/_基于IMX6ULL​

参考资料，GIT仓库里：

  • 芯片资料

    • IMX6ULL/开发板配套资料/datasheet/Core_board/CPU/IMX6ULLRM.pdf

  • 《Chapter 34 Enhanced LCD Interface (eLCDIF)》

  • IMX6ULL的LCD裸机程序

    • IMX6ULL/source/03_LCD/05_参考的裸机源码/03_font_test

  • 内核自带的IMX6ULL LCD驱动程序

    • 驱动源码：Linux-4.9.88/drivers/video/fbdev/mxsfb.c
    • 设备树：

  • arch/arm/boot/dts/imx6ull.dtsi

  • arch/arm/boot/dts/100ask_imx6ull-14x14.dts

  • 本节视频编写好的代码

    • IMX6ULL/source/03_LCD/08_lcd_drv_clk_config_use_devicetree

  • 引脚配置工具/设备树生成工具

    • 打开：http://download.100ask.net/
    • 找到开发板："100ASK_IMX6ULL_PRO开发板"
    • 下载开发板配套资料
    • 下载完后，工具在如下目录里：

    image-20210121150934195

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. 分析内核自带的驱动程序​

2.1 芯片手册​

image-20210123151827981

2.2 设备树​

参考：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";
                        };

定义了3个时钟：

  • pix：Pixel clock，用于LCD接口，设置为LCD手册上的参数
  • axi：AXI clock，用于传输数据、读写寄存器，使能即可
  • disp_axi：一个虚拟的时钟，可以不用设置

2.3 代码​

  • 获得时钟

    	host->clk_pix = devm_clk_get(&host->pdev->dev, "pix");
    	if (IS_ERR(host->clk_pix)) {
    		host->clk_pix = NULL;
    		ret = PTR_ERR(host->clk_pix);
    		goto fb_release;
    	}

    	host->clk_axi = devm_clk_get(&host->pdev->dev, "axi");
    	if (IS_ERR(host->clk_axi)) {
    		host->clk_axi = NULL;
    		ret = PTR_ERR(host->clk_axi);
    		dev_err(&pdev->dev, "Failed to get axi clock: %d\n", ret);
    		goto fb_release;
    	}

    	host->clk_disp_axi = devm_clk_get(&host->pdev->dev, "disp_axi");
    	if (IS_ERR(host->clk_disp_axi)) {
    		host->clk_disp_axi = NULL;
    		ret = PTR_ERR(host->clk_disp_axi);
    		dev_err(&pdev->dev, "Failed to get disp_axi clock: %d\n", ret);
    		goto fb_release;
    	}

  • 设置频率：只需要设置pixel clock的频率

    		ret = clk_set_rate(host->clk_pix,
    				PICOS2KHZ(fb_info->var.pixclock) * 1000U);

  • 使能时钟

    		clk_enable_pix(host);
    			clk_prepare_enable(host->clk_pix);
    		clk_enable_axi(host);
    			clk_prepare_enable(host->clk_axi);
    		clk_enable_disp_axi(host);
    			clk_prepare_enable(host->clk_disp_axi);

3. 自己写代码​