基于Linux操作系统下的音频设备驱动移植的配置过程是怎样的

1.实验原理

FS-MP1A使用的是CS42L51音频芯片，SoC通过I2C和SAI与其进行数据交互，原理图如下：





SAI2管脚对应关系：







I2C5管脚对应关系：





芯片复位管脚对应关系：

原理图网络编号	对应管脚	管脚功能	管脚功能码
SAI2_MCLKA	PE0	SAI2_MCLK_A	AF10
SAI2_SDB	PF11	SDA2_SD_B	AF10
SAI2_SCKA	PI5	SAI2_SCK_A	AF10
SAI_SDA	PI6	SAI2_SD_A	AF10
SAI2_FSA	PI7	SAI2_FS_A	AF10
AUDIO_RST	PC0	IO	ANALOG
I2C5_SDA	PA11	I2C5_SDA	AF4
I2C5_SCL	PA12	I2C5_SDA	AF4

• SAI2设备树节点
  
  

参考文档：

Documentation/devicetree/bindings/sound/st,stm32-sai.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：

sai2: sai@4400b000 {

compatible = "st,stm32h7-sai";

#address-cells = <1>;

#size-cells = <1>;

ranges = <0 0x4400b000 0x400>;

reg = <0x4400b000 0x4>, <0x4400b3f0 0x10>;

interrupts = ;

resets = <&rcc SAI2_R>;

status = "disabled";


sai2a: audio-controller@4400b004 {

#sound-dai-cells = <0>;

compatible = "st,stm32-sai-sub-a";

reg = <0x4 0x1c>;

clocks = <&rcc SAI2_K>;

clock-names = "sai_ck";

dmas = <&dmamux1 89 0x400 0x01>;

status = "disabled";

};


sai2b: audio-controller@4400b024 {

#sound-dai-cells = <0>;

compatible = "st,stm32-sai-sub-b";

reg = <0x24 0x1c>;

clocks = <&rcc SAI2_K>;

clock-names = "sai_ck";

dmas = <&dmamux1 90 0x400 0x01>;

status = "disabled";

};

};

上述代码只对SAI2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stm32mp15xx-dkx.dtsi对于SAI2设备节点的描述，增加SAI2内容如下：

&sai2 {

clocks = <&rcc SAI2>, <&rcc PLL3_Q>, <&rcc PLL3_R>;

clock-names = "pclk", "x8k", "x11k";

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

pinctrl-0 = <&sai2a_pins_a>, <&sai2b_pins_b>;

pinctrl-1 = <&sai2a_sleep_pins_a>, <&sai2b_sleep_pins_b>;

status = "okay";


sai2a: audio-controller@4400b004 {

#clock-cells = <0>;

dma-names = "tx";

clocks = <&rcc SAI2_K>;

clock-names = "sai_ck";

status = "okay";


sai2a_port: port {

sai2a_endpoint: endpoint {

remote-endpoint = <&cs42l51_tx_endpoint>;

format = "i2s";

mclk-fs = <256>;

dai-tdm-slot-num = <2>;

dai-tdm-slot-width = <32>;

};

};

};


sai2b: audio-controller@4400b024 {

dma-names = "rx";

st,sync = <&sai2a 2>;

clocks = <&rcc SAI2_K>, <&sai2a>;

clock-names = "sai_ck", "MCLK";

status = "okay";

sai2b_port: port {

sai2b_endpoint: endpoint {

remote-endpoint = <&cs42l51_rx_endpoint>;

format = "i2s";

mclk-fs = <256>;

dai-tdm-slot-num = <2>;

dai-tdm-slot-width = <32>;

};

};

};

};

由于stm32mp15-pinctrl.dtsi中对于SAI2管脚的定义与FS-MP1A实际使用管脚一致，所以无需修改。

• CS42L51设备树节点
  
  

由于前文中已经增加过I2C5的节点信息，本节就不再重复，在原有I2C5节点添加CS42L51内容即可。

参考文档：

Documentation/devicetree/bindings/sound/cs42l51.txt

参考stm32mp15xx-dkx.dtsi对于codec芯片设备节点的描述，增加内容如下：

cs42l51: cs42l51@4a {

compatible = "cirrus,cs42l51";

reg = <0x4a>;

#sound-dai-cells = <0>;

VL-supply = <&v3v3>;

VD-supply = <&v1v8_audio>;

VA-supply = <&v1v8_audio>;

VAHP-supply = <&v1v8_audio>;

reset-gpios = <&gpioc 0 GPIO_ACTIVE_LOW>;

clocks = <&sai2a>;

clock-names = "MCLK";

status = "okay";


cs42l51_port: port {

#address-cells = <1>;

#size-cells = <0>;


cs42l51_tx_endpoint: endpoint@0 {

reg = <0>;

remote-endpoint = <&sai2a_endpoint>;

frame-master;

bitclock-master;

};


cs42l51_rx_endpoint: endpoint@1 {

reg = <1>;

remote-endpoint = <&sai2b_endpoint>;

frame-master;

bitclock-master;

};

};

};

• 1.8V电源设备节点
  
  

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&v1v8_audio节点，内容如下：

v1v8_audio: regulator-v1v8_audio {

compatible = "regulator-fixed";

regulator-name = "v1v8_audio";

regulator-min-microvolt = <1800000>;

regulator-max-microvolt = <1800000>;

regulator-always-on;

regulator-boot-on;

};

• SOC声卡驱动节点
  
  

内核中包含audio-graph-card驱动，驱动将声卡各个部分关联起来，驱动正常工作需添加对应设备树节点。

参考文档：

Documentation/devicetree/bindings/sound/audio-graph-card.txt

在根节点写下添加sound节点：


sound {

compatible = "audio-graph-card";

label = "STM32MP1-FSMP1A";

routing =

"Playback" , "MCLK",

"Capture" , "MCLK",

"MICL" , "Mic Bias";

dais = <&sai2a_port &sai2b_port>;

status = "okay";

};

2.实验平台


华清远见开发环境，FS-MP1A平台；

3.实验目的

熟悉基于Linux操作系统下的音频设备驱动移植配置过程。

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

• 添加SAI2节点
  
  

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在文件末尾添加如下内容：

&sai2 {

clocks = <&rcc SAI2>, <&rcc PLL3_Q>, <&rcc PLL3_R>;

clock-names = "pclk", "x8k", "x11k";

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

pinctrl-0 = <&sai2a_pins_a>, <&sai2b_pins_b>;

pinctrl-1 = <&sai2a_sleep_pins_a>, <&sai2b_sleep_pins_b>;

status = "okay";



sai2a: audio-controller@4400b004 {

#clock-cells = <0>;

dma-names = "tx";

clocks = <&rcc SAI2_K>;

clock-names = "sai_ck";

status = "okay";



sai2a_port: port {

sai2a_endpoint: endpoint {

remote-endpoint = <&cs42l51_tx_endpoint>;

format = "i2s";

mclk-fs = <256>;

dai-tdm-slot-num = <2>;

dai-tdm-slot-width = <32>;

};

};

};



sai2b: audio-controller@4400b024 {

dma-names = "rx";

st,sync = <&sai2a 2>;

clocks = <&rcc SAI2_K>, <&sai2a>;

clock-names = "sai_ck", "MCLK";

status = "okay";



sai2b_port: port {

sai2b_endpoint: endpoint {

remote-endpoint = <&cs42l51_rx_endpoint>;

format = "i2s";

mclk-fs = <256>;

dai-tdm-slot-num = <2>;

dai-tdm-slot-width = <32>;

};

};

};

};

• 添加CS42L51节点
  
  

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在I2C5节点中添加如下内容：

cs42l51: cs42l51@4a {

compatible = "cirrus,cs42l51";

reg = <0x4a>;

#sound-dai-cells = <0>;

VL-supply = <&v3v3>;

VD-supply = <&v1v8_audio>;

VA-supply = <&v1v8_audio>;

VAHP-supply = <&v1v8_audio>;

reset-gpios = <&gpioc 0 GPIO_ACTIVE_LOW>;

clocks = <&sai2a>;

clock-names = "MCLK";

status = "okay";



cs42l51_port: port {

#address-cells = <1>;

#size-cells = <0>;



cs42l51_tx_endpoint: endpoint@0 {

reg = <0>;

remote-endpoint = <&sai2a_endpoint>;

frame-master;

bitclock-master;

};



cs42l51_rx_endpoint: endpoint@1 {

reg = <1>;

remote-endpoint = <&sai2b_endpoint>;

frame-master;

bitclock-master;

};

};

};

• 添加v1v8_audio电源节点
  
  

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在根节点中添加如下内容：

v1v8_audio: regulator-v1v8_audio {

compatible = "regulator-fixed";

regulator-name = "v1v8_audio";

regulator-min-microvolt = <1800000>;

regulator-max-microvolt = <1800000>;

regulator-always-on;

regulator-boot-on;

};

• 添加Sound节点
  
  

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在根节点中添加如下内容：

sound {

compatible = "audio-graph-card";

label = "STM32MP1-FSMP1A";

routing =

"Playback" , "MCLK",

"Capture" , "MCLK",

"MICL" , "Mic Bias";

dais = <&sai2a_port &sai2b_port>;

status = "okay";

};

• 配置内核
  
  

由于内核源码默认配置以及支持CS42L51，本节列出主要选项，如下：

linux@ubuntu:$ make menuconfig

Device Drivers --->

<*> Sound card support --->

<*> Advanced Linux Sound Architecture --->

<*> ALSA for SoC audio support --->

STMicroelectronics STM32 SOC audio support --->

<*> STM32 SAI interface (Serial Audio Interface) support

CODEC drivers --->

<*> Cirrus Logic CS42L51 CODEC (I2C)

<*> ASoC Audio Graph sound card 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，启动后启动信息中出现如下内容：






插上耳机，终端输入录音命令：

root@fsmp1a:# arecord -D record_codec -f S16_LE -d 10 test.wav

终端输入播放命令：

root@fsmp1a:# aplay test.wav

注意：由于3.5mm的4段式耳机接口还分为两种，一种是美标版（CTIA），也称为“苹果标准”，同时小米、魅族也是使用这种标准；另外一种是国标版（OMTP），也称为“诺基亚标准”，现在绝大多数诺基亚和大多数国产手机都是使用这种标准。FS-MP1A使用的是国标版，所以部分耳机并不能正常实现录播功能。