STM32MP157 Linux系统移植开发篇16：Linux内核音频驱动移植
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
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_MCLKAPE0SAI2_MCLK_AAF10SAI2_SDBPF11SDA2_SD_BAF10SAI2_SCKAPI5SAI2_SCK_AAF10SAI_SDAPI6SAI2_SD_AAF10SAI2_FSAPI7SAI2_FS_AAF10AUDIO_RSTPC0IOANALOGI2C5_SDAPA11I2C5_SDAAF4I2C5_SCLPA12I2C5_SDAAF4
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 = <GIC_SPI 91 IRQ_TYPE_LEVEL_HIGH>;
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。
硬件平台：华清远见FS-MP1A开发板（STM32MP157）
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