“Linux内核-MIPI LCD驱动移植”的版本间的差异

2021年3月18日 (四) 17:24的版本

实验原理

DSI(Display Serial Interface)，是有MIPI联盟定义的一组通信协议的一部分，MIPI DSI主机控制器是一个数字核心，实现MIPI DSI规范中定义的所有协议功能。它提供了系统和MIPI D_PHY中间的接口，允许用户和符合DSI的显示器进行通信。STM32MP157A系列芯片集成MIPI DSI主机控制器。

MIPI®DSI主机包括内部连接到LTDC的专用视频接口以及一个通用的APB接口，可用于向显示器传输信息。

FS_MP1A提供两组LCD显示接口，分别是RGB和MIPI接口，本节介绍如何在Linux中完成MIPI LCD的支持。

上图为MIPI LCD的接口，接口信号线分为两组，分别是由DSI_D0P、DSI_D0N、DSI_D1P、DSI_D1N、DSI_CKP、DSI_CKN、DSI_TE、DSI_RST、LCD_PWM组成的LCD接口和由I2C2_SCL、I2C2_SDA、TP_RST、TP_IRQ组成的触摸屏接口，本节介绍LCD的支持。

DSI_D0P、DSI_D0N、DSI_D1P、DSI_D1N、DSI_CKP、DSI_CKN是DSI-MIPI的信号线，DSI_TE未使用，DSI_RST是LCD屏复位信号LCD_PWM是背光控制信号。

MIPI LCD接口管脚对应关系：

1. PWM设备节点



参考文档：

Documentation/devicetree/bindings/pwm/pwm-stm32.txt

内核中ST对STM32MP15x系列芯片的设备树资源了做了定义，可参见：

arch/arm/boot/dts/stm32mp151.dtsi

stm32mp151中timers2定义如下：

timers2: timer@40000000 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "st,stm32-timers";
	reg = <0x40000000 0x400>;
	clocks = <&rcc TIM2_K>;
	clock-names = "int";
	dmas = <&dmamux1 18 0x400 0x80000001>,
	       <&dmamux1 19 0x400 0x80000001>,
	       <&dmamux1 20 0x400 0x80000001>,
	       <&dmamux1 21 0x400 0x80000001>,
	       <&dmamux1 22 0x400 0x80000001>;
	dma-names = "ch1", "ch2", "ch3", "ch4", "up";
	status = "disabled";

	pwm {
		compatible = "st,stm32-pwm";
		#pwm-cells = <3>;
		status = "disabled";
	};

	timer@1 {
		compatible = "st,stm32h7-timer-trigger";
		reg = <1>;
		status = "disabled";
	};

	counter {
			compatible = "st,stm32-timer-counter";
			status = "disabled";
		};
	};

上述代码只对timers5做了基本的初始化，并没有针对不同的硬件设计做适配，所以需结合硬件补全设备树节点信息。


参考文档或stm32mp15xx-dkx.dtsi对于i2c设备节点的描述，增加timers内容如下：

&timers2 {
	/* spare dmas for other usage */
	/delete-property/dmas;
	/delete-property/dma-names;
	status = "okay";
	pwm2: pwm {
		pinctrl-0 = <&pwm2_pins_b>;
		pinctrl-1 = <&pwm2_sleep_pins_b>;
		pinctrl-names = "default", "sleep";
		#pwm-cells = <2>;
		status = "okay";
	};
	timer@2 {
		status = "disabled";
	};
};

stm32mp15-pinctrl.dtsi对于pwm2的描述与FS-MP1A所使用管脚不一致，所以无法直接使用，需参考其增加如下内容：

pwm2_pins_b: pwm2-0 {
	pins {
		pinmux = <STM32_PINMUX('A', 5, AF1)>; /* TIM2_CH1 */
		bias-pull-down;
		drive-push-pull;
		slew-rate = <0>;
	};
};
pwm2_sleep_pins_b: pwm1-sleep-0 {
	pins {
		pinmux = <STM32_PINMUX('A', 5, ANALOG)>; /* TIM2_CH1 */
	};
};

2. 背光设备节点



参考文档：

Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
Documentation/devicetree/bindings/leds/backlight/gpio-backlight.txt

FS-MP1A背光可以通过GPIO驱动也可通过PWM2的通道1驱动，可以对比参考文档或内核中其他设备树关于背光的定义。


GPIO驱动背光节点内容如下：

panel_backlight: panel-backlight {
	compatible = "gpio-backlight";
	gpios = <&gpiod 13 GPIO_ACTIVE_LOW>;
		default-on;
	status = "okay";
};

PWM驱动背光节点内容如下：

panel_backlight: panel-backlight {
	compatible = "pwm-backlight";
	pwms = <&pwm2 0 5000000>;
	brightness-levels = <0 4 8 16 32 64 128 255>;
	default-brightness-level = <6>;
	status = "okay";
};

3. LTDC设备节点



参考文档：

Documentation/devicetree/bindings/display/st,stm32-ltdc.txt

由于前面章节已经对LTDC做了讲解，并且已经增加了LTDC的设备节点，本节只需在原有基础上增加DSI对应的数据通道即可。

&ltdc {
	status = "okay";

	port {
		#address-cells = <1>;
		#size-cells = <0>;

		ltdc_ep1_out: endpoint@1 {
			reg = <1>;
			remote-endpoint = <&dsi_in>;
		};
	};
};

4. Panel设备树节点



参考文档：

Documentation/devicetree/bindings/display/panel/panel-dsi-cm.txt

结合参考文档及内核中STM32MP157其他设备树文件，Panel设备树节点为：

panel: panel@0 {
	compatible = "sitronix,st7701";
	reg = <0>;
	reset-gpios = <&gpiog 9 GPIO_ACTIVE_HIGH>;
	power-supply = <&v3v3>;
	status = "okay";

	port {
		panel_in: endpoint {
			remote-endpoint = <&dsi_out>;
		};
	};
};

5. DSI设备树节点



参考文档：

Documentation/devicetree/bindings/display/mipi-dsi-bus.txt

内核中ST对STM32MP15x系列芯片的设备树资源了做了定义，可参见：

arch/arm/boot/dts/stm32mp157.dtsi

stm32mp157中dsi定义如下：

dsi: dsi@5a000000 {
		compatible = "st,stm32-dsi";
		reg = <0x5a000000 0x800>;
		phy-dsi-supply = <&reg18>;
		clocks = <&rcc DSI_K>, <&scmi0_clk CK_SCMI0_HSE>, <&rcc DSI_PX>;
		clock-names = "pclk", "ref", "px_clk";
		resets = <&rcc DSI_R>;
		reset-names = "apb";
		status = "disabled";
	};

上述代码只对dsi做了基本的初始化，并没有针对不同的硬件设计做适配，所以需结合硬件补全设备树节点信息。补齐后内容如下：

&dsi {
	#address-cells = <1>;
	#size-cells = <0>;
	status = "okay";

	ports {
		#address-cells = <1>;
		#size-cells = <0>;

		port@0 {
			reg = <0>;
			dsi_in: endpoint {
				remote-endpoint = <&ltdc_ep1_out>;
			};
		};

		port@1 {
			reg = <1>;
			dsi_out: endpoint {
				remote-endpoint = <&dsi_panel_in>;
			};
		};
	};

	panel_dsi: panel-dsi@0 {
		compatible = "sitronix,st7701";
		reg = <0>;
		reset-gpios = <&gpiog 9 GPIO_ACTIVE_LOW>;
		backlight = <&panel_backlight>;
		power-supply = <&v3v3>;
		status = "okay";

		port {
			dsi_panel_in: endpoint {
				remote-endpoint = <&dsi_out>;
			};
		};
	};
};

实验目的

熟悉基于Linux操作系统下的MIPI-LCD设备驱动移植配置过程。

实验平台

华清远见开发环境，FS-MP1A平台；

实验步骤

1. 添加MIPI-LCD驱动



FS-MP1A配套MIPI屏幕主控芯片是st7701，内核中并没有提供其的驱动，所以需要移植st7701的驱动


将【华清远见-FS_MP1A开发资料\02-程序源码\04-Linux系统移植\04-移植相关文件\02-Linux内核移植\st7701驱动】下的panel-sitronix-st7701.c复制到内核源码下的drivers/gpu/drm/panel/目录下。

linux@ubuntu $> cp panel-sitronix-st7701.c drivers/gpu/drm/panel/

• 添加pwm2内容
  

修改stm32mp15xx-fsmp1x.dtsi，在stm32mp15xx-fsmp1x.dtsi文件末尾添加如下内容：

&timers2 {
	/* spare dmas for other usage */
	/delete-property/dmas;
	/delete-property/dma-names;
	status = "okay";
	pwm2: pwm {
		pinctrl-0 = <&pwm2_pins_b>;
		pinctrl-1 = <&pwm2_sleep_pins_b>;
		pinctrl-names = "default", "sleep";
		#pwm-cells = <2>;
		status = "okay";
	};
	timer@2 {
		status = "disabled";
	};
};

&pinctrl {
	pwm2_pins_b: pwm2-0 {
		pins {
			pinmux = <STM32_PINMUX('A', 5, AF1)>; /* TIM2_CH1 */
			bias-pull-down;
			drive-push-pull;
			slew-rate = <0>;
		};
	};
	pwm2_sleep_pins_b: pwm1-sleep-0 {
		pins {
			pinmux = <STM32_PINMUX('A', 5, ANALOG)>; /* TIM2_CH1 */
		};
	};
};

• 添加背光内容
  

修改stm32mp15xx-fsmp1x.dtsi，在根节点中添加如下内容：

panel_backlight: panel-backlight {
	compatible = "pwm-backlight";
	pwms = <&pwm2 0 5000000>;
	brightness-levels = <0 4 8 16 32 64 128 255>;
	default-brightness-level = <6>;
	status = "okay";
};

• 增加设备树文件
  

由于MIPI LCD并非FS-MP1A必须配置，本节增加一个设备树文件，对应增加了屏幕的设备。


在内核的arch/arm/boot/dts目录下新建文件stm32mp157a-fsmp1a-mipi050.dts文件并添加如下内容：

#include "stm32mp157a-fsmp1a.dts"

/ {
    model = "HQYJ STM32MP157 FSMP1A MIPI Discovery Board";
    compatible = "st,stm32mp157a-dk1", "st,stm32mp157";
};

由于增加了新的设备树文件需修改arm/arm/boot/dts/Makefile，在文件中增加新的条目，红色字体部分为增加内容

dtb-$(CONFIG_ARCH_STM32) += \


…

stm32mp157a-dk1.dtb \

stm32mp157a-fsmp1a.dtb \

stm32mp157a-fsmp1a-mipi050.dtb \

stm32mp157d-dk1.dtb \

• 添加ltdc内容
  

修改stm32mp15xx-fsmp1x-mipi050.dtsi，在文件末尾添加如下内容：

&ltdc {
	status = "okay";

	port {
		#address-cells = <1>;
		#size-cells = <0>;

		ltdc_ep1_out: endpoint@1 {
			reg = <1>;
			remote-endpoint = <&dsi_in>;
		};
	};
};

• 添加dsi内容
  

修改stm32mp15xx-fsmp1x-mipi050.dtsi，在文件末尾添加如下内容：

&dsi {
	#address-cells = <1>;
	#size-cells = <0>;
	status = "okay";

	ports {
		#address-cells = <1>;
		#size-cells = <0>;

		port@0 {
			reg = <0>;
			dsi_in: endpoint {
				remote-endpoint = <&ltdc_ep1_out>;
			};
		};

		port@1 {
			reg = <1>;
			dsi_out: endpoint {
				remote-endpoint = <&dsi_panel_in>;
			};
		};
	};

	panel_dsi: panel-dsi@0 {
		compatible = "sitronix,st7701";
		reg = <0>;
		reset-gpios = <&gpiof 15 GPIO_ACTIVE_LOW>;
		backlight = <&panel_backlight>;
		power-supply = <&v3v3>;
		status = "okay";

		port {
			dsi_panel_in: endpoint {
				remote-endpoint = <&dsi_out>;
			};
		};
	};
};

• 配置内核
  

配置内核支持st7701，并列出主要选项，如下：

linux@ubuntu:$ make menuconfig
Device Drivers  --->
	Graphics support  --->
		<*> Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)  --->
		<*> DRM Support for STMicroelectronics SoC Series
		<*>   STMicroelectronics specific extensions for Synopsys MIPI DSI
		Display Panels  --->
			<*> Sitronix ST7701 panel driver
		Backlight & LCD device support  --->
			<*>   Generic PWM based Backlight Driver
			<*>   Generic GPIO based Backlight Driver