Linux操作系统下的摄像头设备是如何实现驱动并移植的

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 = ;

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
  
  
  linux@ubuntu:$ make -j4 uImage dtbs LOADADDR=0xC2000040
  
  
  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。