查看“Linux内核-MIPI LCD驱动移植”的源代码

==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。<br>

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。<br>

[[Image:52-1-1-1.png]] <br>

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。<br>


[[Image:52-1-1-2.png]] <br>

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。<br>

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。<br>

MIPI LCD接口管脚对应关系：

[[Image:52-1-1-3.png]] <br>

[[Image:52-1-1-4.png]] <br>

[[Image:52-1-1-5.png]] <br>

[[Image:52-1-1-6.png]] <br>

{|class="wikitable"
|-
! 原理图网络编号 !! 对应管脚 !! 管脚功能 !! 管脚功能码
|-
| DSI_D0P
| DSI_D0P 
| DSI_D0P
| DSI信号线对应管脚为单一功能管脚
|-
| DSI_D0N 
| DSI_D0N 
| DSI_D0N
| DSI信号线对应管脚为单一功能管脚
|-
| DSI_D1P
| DSI_D1P
| DSI_D1P
| DSI信号线对应管脚为单一功能管脚
|-
| DSI_D1N
| DSI_D1N
| DSI_D1N
| DSI信号线对应管脚为单一功能管脚
|-
| DSI_CKP
| DSI_CKP
| DSI_CKP
| DSI信号线对应管脚为单一功能管脚
|-
| DSI_CKN
| DSI_CKN
| DSI_CKN
| DSI信号线对应管脚为单一功能管脚
|-
| DSI_TE
| PC6
| IO
|  
|-
| DSI_RST
| PG9
| IO
|  
|-
| LCD_PWM
| PA5
| TIM2_CH1
| AF1
|}
*PWM设备节点<br>

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：	
<pre><nowiki>
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";
		};
	};
</nowiki></pre>
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。<br>

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：
<pre><nowiki>
&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";
	};
};
</nowiki></pre>
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：
<pre><nowiki>
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 */
	};
};
</nowiki></pre>
*背光设备节点<br>

参考文档：
<pre><nowiki>
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
Documentation/devicetree/bindings/leds/backlight/gpio-backlight.txt
</nowiki></pre>
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。<br>

GPIO驱动背光节点内容如下：
<pre><nowiki>
panel_backlight: panel-backlight {
	compatible = "gpio-backlight";
	gpios = <&gpiod 13 GPIO_ACTIVE_LOW>;
		default-on;
	status = "okay";
};
</nowiki></pre>
PWM驱动背光节点内容如下：
<pre><nowiki>
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";
};
</nowiki></pre>
*LTDC设备节点<br>

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。
<pre><nowiki>
&ltdc {
	status = "okay";

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

		ltdc_ep1_out: endpoint@1 {
			reg = <1>;
			remote-endpoint = <&dsi_in>;
		};
	};
};
</nowiki></pre>
*Panel设备树节点<br>

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：
<pre><nowiki>
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>;
		};
	};
};
</nowiki></pre>
*DSI设备树节点<br>

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：
<pre><nowiki>
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";
	};
</nowiki></pre>
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：
<pre><nowiki>
&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>;
			};
		};
	};
};
</nowiki></pre>

==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==