本文章为《STM32MP157 Linux系统移植开发篇》系列中的一篇，笔者使用的开发平台为华清远见FS-MP1A开发板（STM32MP157开发板）。stm32mp157是ARM双核，2个A7核，1个M4核，A7核上可以跑Linux操作系统，M4核上可以跑FreeRTOS、RT-Thread等实时操作系统，STM32MP157开发板所以既可以学嵌入式linux，也可以学stm32单片机。
针对FS-MP1A开发板，除了Linux系统移植篇外，还包括其他多系列教程，包括Cortex-A7开发篇、Cortex-M4开发篇、扩展板驱动移植篇、Linux应用开发篇、FreeRTOS系统移植篇、Linux驱动开发篇、硬件设计篇、人工智能机器视觉篇、Qt应用编程篇、Qt综合项目实战篇等。欢迎关注，更多stm32mp157开发教程及视频，可加技术交流Q群459754978，感谢关注。
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1.实验原理
DCMI(Digital Camera Interface)，DCMI是一个同步并行接口，能够从外部8bit、10bit、12bit或14bit的CMOS摄像头接收高速数据流，支持不同的数据格式：YCbCr4:2:2/RGB565渐进式视频和压缩数据（JPEG）。
FS-MP1A可以外接8bit的COM Camera，接口定义如下:
接口与MPU管脚对应关系如下：
| 原理图网络编号 | 对应管脚 | 管脚功能 | 管脚功能码 |
| DCMI_D0 | PH9 | DCMI_D0 | AF13 |
| DCMI_D1 | PH10 | DCMI_D0 | AF13 |
| DCMI_D2 | PH11 | DCMI_D0 | AF13 |
| DCMI_D3 | PH12 | DCMI_D0 | AF13 |
| DCMI_D4 | PH14 | DCMI_D0 | AF13 |
| DCMI_D5 | PI4 | DCMI_D0 | AF13 |
| DCMI_D6 | PB8 | DCMI_D0 | AF13 |
| DCMI_D7 | PE6 | DCMI_D0 | AF13 |
| DCMI_RESET | PA3 | GPIO | ANALOG |
| DCMI_PWDN | PA4 | GPIO | ANALOG |
| DCMI_PIXCK | PA6 | DCMI_PIXCLK | AF13 |
| DCMI_VSYNC | PB7 | DCMI_VSYNC | AF13 |
- DCMI设备树节点
参考文档：
Documentation/devicetree/bindings/media/st,stm32-dcmi.txt
Documentation/devicetree/bindings/media/video-interfaces.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dcmi定义如下：
dcmi: dcmi@4c006000 {
compatible = "st,stm32-dcmi";
reg = <0x4c006000 0x400>;
interrupts = <GIC_SPI 78 IRQ_TYPE_LEVEL_HIGH>;
resets = <&rcc CAMITF_R>;
clocks = <&rcc DCMI>;
clock-names = "mclk";
dmas = <&dmamux1 75 0x400 0xe0000001>;
dma-names = "tx";
status = "disabled";
};
上述代码只对dcmi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。
参考帮助文档及内核中其它STM32MP157设备树中对于dcmi的定义，修改dcmi内容如下：
&dcmi {
status = "okay";
pinctrl-names = "default", "sleep";
pinctrl-0 = <&dcmi_pins_a>;
pinctrl-1 = <&dcmi_sleep_pins_a>;
port {
dcmi_0: endpoint {
remote-endpoint = <&ov5640_0>;
bus-width = <8>;
hsync-active = <0>;
vsync-active = <0>;
pclk-sample = <1>;
pclk-max-frequency = <77000000>;
};
};
};
由于stm32mp15-pinctrl.dtsi中对于DCMI管脚的定义与FS-MP1A实际使用管脚一致，所以无需修改
- CMOS Camera设备树节点
FS-MP1A支持多款COMS Camera，本节以ov5640为例：
参考文档：
Documentation/devicetree/bindings/media/i2c/ov5640.txt
参考帮助文档及内核中其它STM32MP157设备树中对于ov5640的定义，修改dcmi内容如下：
ov5640: camera@3c {
compatible = "ovti,ov5640";
reg = <0x3c>;
clocks = <&clk_ext_camera>;
clock-names = "xclk";
DOVDD-supply = <&v2v8>;
powerdown-gpios = <&gpioa 4 (GPIO_ACTIVE_HIGH | GPIO_PUSH_PULL)>;
reset-gpios = <&gpioa 3 (GPIO_ACTIVE_LOW | GPIO_PUSH_PULL)>;
rotation = <180>;
status = "okay";
port {
ov5640_0: endpoint {
remote-endpoint = <&dcmi_0>;
bus-width = <8>;
data-shift = <2>; /* lines 9:2 are used */
hsync-active = <0>;
vsync-active = <0>;
pclk-sample = <1>;
pclk-max-frequency = <77000000>;
};
};
};
- 2.8V电源定义
前文已经说过如何添加电源节点，本节不再重复，在根节点添加&v2v8节点，内容如下：
v2v8_audio: regulator-v2v8 {
compatible = "regulator-fixed";
regulator-name = "v2v8";
regulator-min-microvolt = <2800000>;
regulator-max-microvolt = <2800000>;
regulator-always-on;
regulator-boot-on;
};
- 24M时钟定义
参考文档：
Documentation/devicetree/bindings/clock/fixed-clock.yaml
参考帮助文档或内核中其他设备树文件，对于时钟的定义，增加内容如下：
clocks {
clk_ext_camera: clk-ext-camera {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <24000000>;
};
};
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
- 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
- 增加DCMI设备树节点
修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在文件末尾添加如下内容：
&dcmi {
status = "okay";
pinctrl-names = "default", "sleep";
pinctrl-0 = <&dcmi_pins_a>;
pinctrl-1 = <&dcmi_sleep_pins_a>;
port {
dcmi_0: endpoint {
remote-endpoint = <&ov5640_0>;
bus-width = <8>;
hsync-active = <0>;
vsync-active = <0>;
pclk-sample = <1>;
pclk-max-frequency = <77000000>;
};
};
};
- 增加OV5640节点
修改arch/arm/dts/stm32mp15xx-fsmp1x.dtsi文件，在I2C5节点中添加OV5640设备信息，红色字体为增加内容：
&i2c5 {
pinctrl-names = "default", "sleep";
pinctrl-0 = <&i2c5_pins_a>;
……
ov5640: camera@3c {
compatible = "ovti,ov5640";
reg = <0x3c>;
clocks = <&clk_ext_camera>;
clock-names = "xclk";
DOVDD-supply = <&v2v8>;
powerdown-gpios = <&gpioa 4 (GPIO_ACTIVE_HIGH | GPIO_PUSH_PULL)>;
reset-gpios = <&gpioa 3 (GPIO_ACTIVE_LOW | GPIO_PUSH_PULL)>;
rotation = <180>;
status = "okay";
port {
ov5640_0: endpoint {
remote-endpoint = <&dcmi_0>;
bus-width = <8>;
data-shift = <2>; /* lines 9:2 are used */
hsync-active = <0>;
vsync-active = <0>;
pclk-sample = <1>;
pclk-max-frequency = <77000000>;
};
};
};
};
- 增加2.8V电源和24M时钟
修改arch/arm/dts/stm32mp15xx-fsmp1x.dtsi文件，在根节点最后添加2.8V电源和24M时钟，红色字体为增加内容：
/ {
memory@c0000000 {
device_type = "memory";
reg = <0xc0000000 0x20000000>;
};
……
v2v8: regulator-2p8v {
compatible = "regulator-fixed";
regulator-name = "v2v8";
regulator-min-microvolt = <2800000>;
regulator-max-microvolt = <2800000>;
regulator-always-on;
regulator-boot-on;
};
clocks {
clk_ext_camera: clk-ext-camera {
#clock-cells = <0>;
compatible = "fixed-clock";
clock-frequency = <24000000>;
};
};
};
- 配置内核
配置内核支持ov5640，并列出主要选项，如下
linux@ubuntu:$ make menuconfig
Device Drivers --->
<*> Multimedia support --->
[*] V4L platform devices --->
<*> STM32 Digital Camera Memory Interface (DCMI) support
I2C Encoders, decoders, sensors and other helper chips --->
<*> OmniVision OV5640 sensor support
- 编译内核及设备树
linux@ubuntu:$ make -j4 uImage dtbs LOADADDR=0xC2000040
- 重启测试
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，系统启动后启动信息中包含如下信息：
在屏幕的界面上选择“Camera preview”应用进入摄像头预览程序，启动界面后即可看到摄像头实时采集的图像。
硬件平台：华清远见FS-MP1A开发板（STM32MP157）
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