Linux内核-摄像头驱动移植

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>;
	};
};