一、 概念

CPU DAI:主控端的 Audio Data Interface，比如 I2S,Spdif,Pdm,Tdm (通常所說的platform層)

CODEC DAI：即 Codec將數字信號轉換為模擬音頻輸出的新品（通常所說的codec層）

DAI_LINK:綁定 Cpu_Dai 和 Codec_Dai 為一個聲卡，等同于 Machine Driver。（通常所說的platform層）

DMAENGINE：用于 Cpu 和 I2S/Spdif 等 Dai 之間的 Dma 傳輸引擎，實際是通過 Dma
來進行數據的搬運。（其實是包含在platform層中）

DAPM：動態音頻電源管理，用于動態管理 Codec 等的電源管理，根據通路的開啟配置開
關，以達到保證功能的前提下功耗盡量小。

JACK:耳機的接口檢測，大部分使用 Codec 自身的檢測機制，小部分使用 IO 來進行模擬。

主要理解核心思想是alsa將底層硬件的不同做了抽象分別是cpu digital audio interface的不同，聲卡codec的不同，以及如何將這兩者進行關聯的中介machine driver ：dai link，通常名字是chipName_codecName.c；
simple_card架構即是簡單通用的machine driver即dai_link

二、代碼結構

項目功能路徑

Sound soc	主要包含公共部分代碼，包括dapm 控制， jack， dmaengine，core 等等	sound/soc/
rockchip platform	Rockchip 平臺的 cpu dai 的驅動，比如 I2S, spdif 等以及自定義聲卡machine driver	sound/soc/rockchip
generic platform	simple card framework	sound/soc/generic
codec driver	所有的 codec driver 存放位置	sound/soc/codecs

開發步驟

一個聲卡包含 cpu_dai, codec_dai, 以及 dai_link 組成，分別對應 cpu dai 的 dirver，比如I2S driver, spdif driver； codec driver， 比如 rk817 codec driver； dai_link driver，也就是 machine driver， 比如 sound/soc/rockchip/rockchip_rt5640.c。 4.4 的內核中支持兩種方式創建聲卡，一種是通用的 simple-card framework，一種是傳統的編寫自定義的 machinedriver 來創建。 本文以 rk817 為例。

添加 codec driver，比如添加： sound/soc/codec/rk817_codec.c

修改 sound/soc/codec/Kconfig 以及 Makefile 加入驅動編譯。

sound/soc/codec/Kconfig:tristate "Rockchip RK817 CODEC"depends on MFD_RK808select REGMAP_I2C sound/soc/codec/Makefile: snd-soc-rk817-objs := rk817_codec.oobj-$(CONFIG_SND_SOC_RK817) += snd-soc-rk817.o

menuconfig 中 enable simple card 以及 codec

make menuconfig Device Drivers ---> [*] Sound card support ---> [*] Advanced Linux Sound Architecture ---> [*] ALSA for SoC audio support --->[*] ASoC support for Rockchip[*] Rockchip I2S Device DriverCODEC drivers --->[*] Rockchip RK817 CODEC [*] ASoC Simple sound card support

產品的 DTS 中添加 Simple Card Node

rk809-sound {compatible = "simple-audio-card";simple-audio-card,format = "i2s";simple-audio-card,name = "rockchip,rk809-codec";simple-audio-card,mclk-fs = <256>;simple-audio-card,widgets ="Microphone", "Mic Jack","Headphone", "Headphone Jack";simple-audio-card,routing ="Mic Jack", "MICBIAS1","IN1P", "Mic Jack","Headphone Jack", "HPOL","Headphone Jack", "HPOR";simple-audio-card,cpu {sound-dai = <&i2s1>;};simple-audio-card,codec {sound-dai = <&rk809_codec>;};}; &i2c0 {rk809: pmic@20 {rk809_codec: codec {#sound-dai-cells = <0>;compatible = "rockchip,rk809-codec", "rockchip,rk817-codec";clocks = <&cru SCLK_I2S_8CH_OUT>;clock-names = "mclk";pinctrl-names = "default","spk_gpio";pinctrl-0 = <&i2s_8ch_mclk>;hp-volume = <20>;spk-volume = <3>;io-channels = <&saradc 4>;hp-det-adc-value = <930>;capture-volume = <0>;spk-ctl = <&gpio0 RK_PB1 GPIO_ACTIVE_HIGH>;pinctrl-1 = <&spk_ctl_gpio>;status = "okay";};}; };

5、分析simple-audio-card實現

首先通過打印大致看看：

[ 2.527416] asoc-simple-card rk809-sound: New simple-card: rockchip,rk809-codec [ 2.527458] asoc-simple-card rk809-sound: Revert to legacy daifmt parsing [ 2.527681] asoc-simple-card rk809-sound: name : ff890000.i2s-rk817-hifi [ 2.527702] asoc-simple-card rk809-sound: format : 4001 [ 2.527721] asoc-simple-card rk809-sound: cpu : ff890000.i2s / 0 [ 2.527739] asoc-simple-card rk809-sound: codec : rk817-hifi / 0 [ 2.527761] of_get_named_gpiod_flags: can't parse 'simple-audio-card,hp-det-gpio' property of node '/rk809-sound[0]' [ 2.527782] of_get_named_gpiod_flags: can't parse 'simple-audio-card,mic-det-gpio' property of node '/rk809-sound[0]' [ 2.536256] asoc-simple-card rk809-sound: rk817-hifi <-> ff890000.i2s mapping ok [ 2.536953] asoc-simple-card rk809-sound: ASoC: no source widget found for MICBIAS1 [ 2.537668] asoc-simple-card rk809-sound: ASoC: Failed to add route MICBIAS1 -> direct -> Mic Jack [ 2.538485] asoc-simple-card rk809-sound: ASoC: no sink widget found for IN1P [ 2.539150] asoc-simple-card rk809-sound: ASoC: Failed to add route Mic Jack -> direct -> IN1P [ 2.539924] asoc-simple-card rk809-sound: ASoC: no source widget found for HPOL [ 2.540594] asoc-simple-card rk809-sound: ASoC: Failed to add route HPOL -> direct -> Headphone Jack [ 2.541425] asoc-simple-card rk809-sound: ASoC: no source widget found for HPOR [ 2.542098] asoc-simple-card rk809-sound: ASoC: Failed to add route HPOR -> direct -> Headphone Jack [ 2.544603] input: rockchip,rk809-codec Headphone Jack as /devices/platform/rk809-sound/sound/card1/input4

kernel/sound/soc/generic/simple-card.c
函數調用順序大致如下：

static const struct of_device_id asoc_simple_of_match[] = {{ .compatible = "simple-audio-card", },{}, };

通過driver platform框架我們可以知道下面會調用probe函數

asoc_simple_card_probeasoc_simple_card_parse_ofsnd_soc_of_parse_card_name(&priv->snd_card, "simple-audio-card,name");//拿到卡的名字即dts中rockchip,rk809-codec/* For single DAI link & old style of DT node */asoc_simple_card_dai_link_of //連接cpu dai與codec daiasoc_simple_card_sub_parse_of(cpu, &dai_props->cpu_dai,&dai_link->cpu_of_node,&dai_link->cpu_dai_name,&cpu_args); //拿到cpu daiasoc_simple_card_sub_parse_of(codec, &dai_props->codec_dai,&dai_link->codec_of_node,&dai_link->codec_dai_name, NULL;//拿到codec dai//soc/soc-core.c +3606of_parse_phandle_with_args(of_node, "sound-dai","#sound-dai-cells", 0, &args);//#sound-dai-cells 在dts中是0，即rk817_codec.c中的struct snd_soc_dai_driver rk817_dai[0]節點 即rk817-hifi。snd_soc_of_get_dai_name(np, name); //拿到dai name//注冊聲卡 snd_soc_card_set_drvdata(&priv->snd_card, priv);ret = devm_snd_soc_register_card(&pdev->dev, &priv->snd_card);

這個達到的效果跟machine driver是一樣的，只不過這個屬于讀取dts然后批量注冊聲卡，更加簡單高效。

總結

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