STM32MP157 Linux系统移植开发篇14：Linux内核RGB LCD驱动移植

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STMCU小助手发布时间：2022-9-30 16:02

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文章简介:	STM32MP157 Linux系统移植开发篇14：Linux内核RGB LCD驱动移植

1.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。

1.驱动修改
驱动路径为：drivers/gpu/drm/panel/panel-simple.c

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：

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,
};

复制代码

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：

hdisplay：有效显示区水平像素数量，对应Active Width

hsync_start：水平同步开始，对应hdispay + HFP

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

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

vdisplay：垂直显示像素，对应Active Height

vsync_start：垂直同步开始，对应vdispay + VFP

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

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

vrefresh：刷新率

面板芯片手册中关于时序的描述如下：

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：

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,

};

2.设备树修改
增加ltdc输出端口：

<dc {

status = "okay";

port {

#address-cells = <1>;

#size-cells = <0>;

ltdc_ep1_out: endpoint@1 {

reg = <1>;

remote-endpoint = <&panel_in_rgb>;

};

};

};

3.增加面板节点：

panel: panel-rgb {

compatible = "innolux,zj070na-01p";

pinctrl-names = "default", "sleep";

backlight = <&panel_backlight>;

status = "okay";

port {

panel_in_rgb: endpoint {

remote-endpoint = <<dc_ep1_out>;

};

};

};

4.PWM设备节点

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 */

};

};

5.背光设备节点

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";

};

2.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。

3.实验平台
华清远见开发环境，FS-MP1A平台；

4.实验步骤
1.导入交叉编译工具链
linux@ubuntu

source /opt/st/stm32mp1/3.1-openstlinux-5.4-dunfell-mp1-20-06-24/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi

2.增加设备树文件
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。

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：

#include "stm32mp157a-fsmp1a.dts"

/ {

model = "HQYJ STM32MP157 FSMP1A RGB Discovery Board";

compatible = "st,stm32mp157a-dk1", "st,stm32mp157";

};

由于增加了新的设备树文件需修改arch/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 \

stm32mp157a-fsmp1a-rgb070.dtb \

stm32mp157d-dk1.dtb \

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 */

};

};

};

3.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";

};

4.添加ltdc端口
修改文件arm/arm/boot/dts/stm32mp157a-fsmp1a-rgb070.dts，在文件末尾添加如下内容：

<dc {

status = "okay";

port {

#address-cells = <1>;

#size-cells = <0>;

ltdc_ep1_out: endpoint@1 {

reg = <1>;

remote-endpoint = <&panel_in_rgb>;

};

};

};

5.添加面板信息
修改文件arm/arm/boot/dts/stm32mp157a-fsmp1a-rgb070.dts，在根节点中添加如下内容：

panel: panel-rgb {

compatible = "innolux,zj070na-01p";

pinctrl-names = "default", "sleep";

backlight = <&panel_backlight>;

status = "okay";

port {

panel_in_rgb: endpoint {

remote-endpoint = <<dc_ep1_out>;

};

};

};

修改面板驱动，修改面板时序参数
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：

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,

};

6.配置内核
由于内核默认支持通用面板驱动，本节列出主要选项，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

Display Panels --->

<*> support for simple panels

Backlight & LCD device support --->

<*> Generic PWM based Backlight Driver

7.增加启动项
在虚拟机/tftpboot /tftpboot/pxelinux.cfg/01-00-80-e1-42-60-17末尾添加

LABEL stm32mp157a-fsmp1a-mipi
KERNEL /uImage
FDT /stm32mp157a-fsmp1a-rgb070.dtb
APPEND root=/dev/mmcblk1p4 rootwait rw console=ttySTM0,115200

8.编译内核及设备树
linux@ubuntu

make -j4 uImage dtbs LOADADDR=0xC2000040

9.重启测试
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。