查看“Linux内核-音频驱动移植”的源代码

==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：<br>

[[Image:57-1-1-1.png|640px]] <br>

SAI2管脚对应关系：

[[Image:57-1-1-2.png]] <br>

[[Image:57-1-1-3.png]] <br>

[[Image:57-1-1-4.png]] <br>

I2C5管脚对应关系：

[[Image:57-1-1-5.png]] <br>

芯片复位管脚对应关系：

[[Image:57-1-1-6.png]] <br>

{|class="wikitable"
|-
! 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
|}
<ol>
<li>SAI2设备树节点</li>

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：
<pre><nowiki>
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";
	};
};
</nowiki></pre>
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。<br>

参考stm32mp15xx-dkx.dtsi对于SAI2设备节点的描述，增加SAI2内容如下：
<pre><nowiki>
&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>;
			};
		};
	};
};
</nowiki></pre>
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。<br>

<li>CS42L51设备树节点</li>

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。<br>

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：
<pre><nowiki>
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;
		};
	};
};
</nowiki></pre>
<li>1.8V电源设备节点</li>
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：
<pre><nowiki>
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;
};
</nowiki></pre>
<li>SOC声卡驱动节点</li>

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。<br>

参考文档：
 Documentation/devicetree/bindings/sound/audio-graph-card.txt
在根节点写下添加sound节点：
<pre><nowiki>
sound {
	compatible = "audio-graph-card";
	label = "STM32MP1-FSMP1A";
	routing =
		"Playback" , "MCLK",
		"Capture" , "MCLK",
		"MICL" , "Mic Bias";
	dais = <&sai2a_port &sai2b_port>;
	status = "okay";
};
</nowiki></pre>
</ol>

==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。

==实验平台==
华清远见开发环境，FS-MP1A平台；

==实验步骤==
<ol>
<li>导入交叉编译工具链</li>
 linux@ubuntu:$ source /opt/st/stm32mp1/3.1-openstlinux-5.4-dunfell-mp1-20-06-24/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi
<li>添加SAI2节点</li>
修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在文件末尾添加如下内容：
<pre><nowiki>
&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>;
			};
		};
	};
};
&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>;
			};
		};
	};
};

</nowiki></pre>

<li>添加CS42L51节点</li>
修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在I2C5节点中添加如下内容：
<pre>
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;
		};
	};
};
</pre>
<li>添加v1v8_audio电源节点</li>

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

</nowiki></pre>
<li>添加Sound节点</li>

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在根节点中添加如下内容：
<pre><nowiki>
sound {
	compatible = "audio-graph-card";
	label = "STM32MP1-FSMP1A";
	routing =
		"Playback" , "MCLK",
		"Capture" , "MCLK",
		"MICL" , "Mic Bias";
	dais = <&sai2a_port &sai2b_port>;
	status = "okay";
};
</nowiki></pre>
<li>配置内核</li>

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：
<pre><nowiki>
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

</nowiki></pre>
<li>编译内核及设备树</li>
 linux@ubuntu:$ make -j4 uImage dtbs LOADADDR=0xC2000040
<li>重启测试</li>

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：

[[Image:57-1-4-1.png]] <br>

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
<font color="#FF0000">
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。
</font>
</ol>