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]] <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
|}
*SAI2设备树节点<br>

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>

*CS42L51设备树节点<br>

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>
*1.8V电源设备节点<br>
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>
*SOC声卡驱动节点<br>

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>

==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==