STM32MP157 Linux系統移植開發篇17：Linux內核攝像頭驅動移植

本文章為《STM32MP157 Linux系統移植開發篇》系列中的一篇，筆者使用的開發平臺為華清遠見FS-MP1A開發板（STM32MP157開發板），stm32mp157是ARM雙核，2個A7核，1個M4核，A7核上可以跑Linux作業系統，M4核上可以跑FreeRTOS、RT-Thread等實時作業系統，STM32MP157開發板所以既可以學嵌入式linux，也可以學stm32單片機，

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1.實驗原理

DCMI(Digital Camera Interface)，DCMI是一個同步并行介面，能夠從外部8bit、10bit、12bit或14bit的CMOS攝像頭接收高速資料流，支持不同的資料格式：YCbCr4:2:2/RGB565漸進式視頻和壓縮資料（JPEG），

FS-MP1A可以外接8bit的COM Camera，介面定義如下:

介面與MPU管腳對應關系如下：

1. DCMI設備樹節點

參考檔案：

Documentation/devicetree/bindings/media/st,stm32-dcmi.txt

Documentation/devicetree/bindings/media/video-interfaces.txt

內核中ST對STM32MP15x系列芯片的設備樹資源了做了定義，可參見：

arch/arm/boot/dts/stm32mp151.dtsi

stm32mp151中dcmi定義如下：

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";

};

上述代碼只對dcmi做了基本的初始化，并沒有針對不同的硬體設計做適配，所以需結合硬體補全設備樹節點資訊，

參考幫助檔案及內核中其它STM32MP157設備樹中對于dcmi的定義，修改dcmi內容如下：

&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中對于DCMI管腳的定義與FS-MP1A實際使用管腳一致，所以無需修改

1. CMOS Camera設備樹節點

FS-MP1A支持多款COMS Camera，本節以ov5640為例：

參考檔案：

Documentation/devicetree/bindings/media/i2c/ov5640.txt

參考幫助檔案及內核中其它STM32MP157設備樹中對于ov5640的定義，修改dcmi內容如下：

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>;

};

};

};

1. 2.8V電源定義

前文已經說過如何添加電源節點，本節不再重復，在根節點添加&v2v8節點，內容如下：

v2v8_audio: regulator-v2v8 {

compatible = "regulator-fixed";

regulator-name = "v2v8";

regulator-min-microvolt = <2800000>;

regulator-max-microvolt = <2800000>;

regulator-always-on;

regulator-boot-on;

};

1. 24M時鐘定義

參考檔案：

Documentation/devicetree/bindings/clock/fixed-clock.yaml

參考幫助檔案或內核中其他設備樹檔案，對于時鐘的定義，增加內容如下：

clocks {

clk_ext_camera: clk-ext-camera {

#clock-cells = <0>;

compatible = "fixed-clock";

clock-frequency = <24000000>;

};

};

2.實驗目的

熟悉基于Linux作業系統下的攝像頭設備驅動移植配置程序，

3.實驗平臺

華清遠見開發環境，FS-MP1A平臺；

4.實驗步驟

1. 匯入交叉編譯工具鏈

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

1. 增加DCMI設備樹節點

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi檔案，在檔案末尾添加如下內容：

&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>;

};

};

};

1. 增加OV5640節點

修改arch/arm/dts/stm32mp15xx-fsmp1x.dtsi檔案，在I2C5節點中添加OV5640設備資訊，紅色字體為增加內容：

&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>;

};

};

};

};

1. 增加2.8V電源和24M時鐘

修改arch/arm/dts/stm32mp15xx-fsmp1x.dtsi檔案，在根節點最后添加2.8V電源和24M時鐘，紅色字體為增加內容：

/ {

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>;

};

};

};

1. 配置內核

配置內核支持ov5640，并列出主要選項，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

1. 編譯內核及設備樹

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

1. 重啟測驗

將編譯好的設備樹和內核鏡像拷貝到/tftpboot目錄下，通過tftp引導內核，系統啟動后啟動資訊中包含如下資訊：

在螢屏的界面上選擇“Camera preview”應用進入攝像頭預覽程式，啟動界面后即可看到攝像頭實時采集的影像，

硬體平臺：華清遠見FS-MP1A開發板（STM32MP157）

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