查看“Linux内核-RGB LCD驱动移植”的源代码

==实验原理==
前文介绍过LTDC的内容，本节只需为LTDC添加一个面板即可。内核中包含一个通用的面板驱动，驱动之包含大量各种各样的面板。<br>
<ol>
<li>驱动修改</li>

驱动路径为：drivers/gpu/drm/panel/panel-simple.c<br>

移植时可以在驱动中支持新的面板的内容，也可以找到一个与自己面板相仿的内容进行修改，本节即使用在原有面板修改的方法。如本节参考面板名称为zj070na-01p，对于一个面板最关键的内容在驱动通过drm_display_mode的结构体描述，zj070na-01p的描述如下：
<pre><nowiki>
static const struct drm_display_mode innolux_zj070na_01p_mode = {
	.clock = 51501,
	.hdisplay = 1024,
	.hsync_start = 1024 + 128,
	.hsync_end = 1024 + 128 + 64,
	.htotal = 1024 + 128 + 64 + 128,
	.vdisplay = 600,
	.vsync_start = 600 + 16,
	.vsync_end = 600 + 16 + 4,
	.vtotal = 600 + 16 + 4 + 16,
	.vrefresh = 60,
};
</nowiki></pre>
这个结构体主要用来描述面板的时序相关信息，时序框图如下：

<center>[[Image:55-1-1-1.png|640px]]</center> <br>

hdisplay：有效显示区水平像素数量，对应Active Width<br>

hsync_start：水平同步开始，对应hdispay + HFP<br>

hsync_end：水平同步结束，对应hdisplay + HFP + HSYNC width(HPW)<br>

htotal：水平总像素，对应hdisplay + HFP + HSYNC width + HBP<br>

vdisplay：垂直显示像素，对应Active Height<br>

vsync_start：垂直同步开始，对应vdispay + VFP<br>

vsync_end：垂直像素结束，对应vdisplay + VFP + VSYNC width(VPW)<br>

vtotal：垂直总像素，对应vdisplay + VFP + VSYNC width + VBP<br>

vrefresh：刷新率<br>

面板芯片手册中关于时序的描述如下：

<center>[[Image:55-1-1-2.png|640px]]</center> <br>

表中可以确认HBP=140、HPW=20、HFP=160、VBP=20、VPW=3、VFP=12，修改面板信息如下：
<pre><nowiki>
static const struct drm_display_mode innolux_zj070na_01p_mode = {
	.clock = 51501,
	.hdisplay = 1024,
	.hsync_start = 1024 + 160,
	.hsync_end = 1024 + 160 + 20,
	.htotal = 1024 + 160 + 20 + 140,
	.vdisplay = 600,
	.vsync_start = 600 + 12,
	.vsync_end = 600 + 12 + 3,
	.vtotal = 600 + 12 + 3 + 12,
	.vrefresh = 60,
};
</nowiki></pre>
<li>设备树修改</li>

增加ltdc输出端口：
<pre><nowiki>
&ltdc {
	status = "okay";

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

		ltdc_ep1_out: endpoint@1 {
			reg = <1>;
			remote-endpoint = <&panel_in_rgb>;
		};
	};
};
</nowiki></pre>
增加面板节点：
<pre><nowiki>
panel: panel-rgb {
	compatible = "innolux,zj070na-01p";
	pinctrl-names = "default", "sleep";
	backlight = <&panel_backlight>;
	status = "okay";

	port {
		panel_in_rgb: endpoint {
			remote-endpoint = <&ltdc_ep1_out>;
		};
	};
};
</nowiki></pre>

<li>PWM设备节点</li>

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。
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>
<li>背光设备节点</li>
参考文档：
<pre>
Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
Documentation/devicetree/bindings/leds/backlight/gpio-backlight.txt
</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。

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

==实验目的==
熟悉基于Linux操作系统下的摄像头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==
<ol>
<li>导入交叉编译工具链</li>
 linux@ubuntu:$ source /opt/st/stm32mp1/3.1-openstlinux-5.4-dunfell-mp1-20-06-24/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi
<li>增加设备树文件</li>

由于RGB 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。<br>

在内核的arch/arm/boot/dts目录下新建文件stm32mp157a-fsmp1a-rgb070.dts文件并添加如下内容：
<pre><nowiki>
#include "stm32mp157a-fsmp1a.dts"

/ {
    model = "HQYJ STM32MP157 FSMP1A RGB Discovery Board";
    compatible = "st,stm32mp157a-dk1", "st,stm32mp157";
};
</nowiki></pre>
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
<div style="background-color:#F8F8F8;border:1px solid #E5E5E5;font-family: monospace,Courier;">
:  dtb-$(CONFIG_ARCH_STM32) += \<br>
::  …
::     stm32mp157a-dk1.dtb \
::     stm32mp157a-fsmp1a.dtb \
::     stm32mp157a-fsmp1a-mipi050.dtb \
<font color="#FF0000">
::     stm32mp157a-fsmp1a-rgb070.dtb \
</font>
::     stm32mp157d-dk1.dtb \
</div>

<li>添加pwm2内容</li>
修改stm32mp15xx-fsmp1x.dtsi，在stm32mp15xx-fsmp1x.dtsi文件末尾添加如下内容：
<pre>
&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 */
		};
	};
};

</pre>
<li>添加背光内容</li>
修改stm32mp15xx-fsmp1x.dtsi，在根节点中添加如下内容：
<pre>
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";
};
</pre>
<li>添加ltdc端口</li>

修改文件arm/arm/boot/dts/stm32mp157a-fsmp1a-rgb070.dts，在文件末尾添加如下内容：
<pre><nowiki>
&ltdc {
	status = "okay";

	port {
		#address-cells = <1>;
		#size-cells = <0>;
		ltdc_ep1_out: endpoint@1 {
			reg = <1>;
			remote-endpoint = <&panel_in_rgb>;
		};
	};
};
</nowiki></pre>
<li>添加面板信息</li>

修改文件arm/arm/boot/dts/stm32mp157a-fsmp1a-rgb070.dts，在根节点中添加如下内容：
<pre><nowiki>
panel: panel-rgb {
	compatible = "innolux,zj070na-01p";
	pinctrl-names = "default", "sleep";
	backlight = <&panel_backlight>;
	status = "okay";
	port {
		panel_in_rgb: endpoint {
			remote-endpoint = <&ltdc_ep1_out>;
		};
	};
};  
</nowiki></pre>
<li>修改面板驱动，修改面板时序参数</li>

修改文件drivers/gpu/drm/panel/panel-simple.c，修改zj070na-01p面板信息，对照面板芯片手册修改原有内容，红色字体部分为修改内容：
<div style="background-color:#F8F8F8;border:1px solid #E5E5E5;font-family: monospace,Courier;">
:static const struct drm_display_mode innolux_zj070na_01p_mode = {
::	.clock = 51501,
::	.hdisplay = 1024,
::	.hsync_start = 1024 + <font color="#FF0000">160</font>,
::	.hsync_end = 1024 + <font color="#FF0000">160 </font>+ <font color="#FF0000">20</font>,
::	.htotal = 1024 + <font color="#FF0000">160</font> + <font color="#FF0000">20</font> + <font color="#FF0000">140</font>,
::	.vdisplay = 600,
::	.vsync_start = 600 + <font color="#FF0000">12</font>,
::	.vsync_end = 600 + <font color="#FF0000">12</font> + <font color="#FF0000">3</font>,
::	.vtotal = 600 + <font color="#FF0000">12</font> + <font color="#FF0000">3</font> + <font color="#FF0000">12</font>,
::	.vrefresh = 60,
};
</div>
<li>配置内核</li>

由于内核默认支持通用面板驱动，本节列出主要选项，如下
<pre><nowiki>
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
		Display Panels  --->
			<*> support for simple panels
		Backlight & LCD device support  --->
			<*>   Generic PWM based Backlight Driver
</nowiki></pre>

<li>增加启动项</li>
在虚拟机/tftpboot /tftpboot/pxelinux.cfg/01-00-80-e1-42-60-17末尾添加
<pre>
LABEL stm32mp157a-fsmp1a-mipi
  KERNEL /uImage
  FDT /stm32mp157a-fsmp1a-rgb070.dtb
  APPEND root=/dev/mmcblk1p4 rootwait rw console=ttySTM0,115200
</pre>

<li>编译内核及设备树</li>
 linux@ubuntu:$ make -j4 uImage dtbs LOADADDR=0xC2000040

<li>重启测试</li>

安装上7寸LCD面板，将编译好的设备树和内核镜像拷贝到/tftpboot目录下，通过tftp引导内核，启动后可正常显示，如果屏幕显示不正可适当调节面板参数。

<center>[[Image:55-1-4-1.png]] </center><br>

</ol>