1. Codec簡介
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對PCM等信號進行D/A轉換,把數字的音頻信號轉換爲模擬信號
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對Mic、Linein或者其他輸入源的模擬信號進行A/D轉換,把模擬的聲音信號轉變CPU能夠處理的數字信號
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對音頻通路進行控制,比如播放音樂,收聽調頻收音機,又或者接聽電話時,音頻信號在codec內的流通路線是不一樣的
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對音頻信號做出相應的處理,例如音量控制,功率放大,EQ控制等等
2. ASoC中對Codec的數據抽象
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/* SoC Audio Codec device */
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struct snd_soc_codec {
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const char *name; /* Codec的名字*/
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struct device *dev; /* 指向Codec設備的指針 */
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const struct snd_soc_codec_driver *driver; /* 指向該codec的驅動的指針 */
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struct snd_soc_card *card; /* 指向Machine驅動的card實例 */
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int num_dai; /* 該Codec數字接口的個數,目前越來越多的Codec帶有多個I2S或者是PCM接口 */
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int (*volatile_register)(...); /* 用於判定某一寄存器是否是volatile */
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int (*readable_register)(...); /* 用於判定某一寄存器是否可讀 */
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int (*writable_register)(...); /* 用於判定某一寄存器是否可寫 */
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/* runtime */
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......
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/* codec IO */
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void *control_data; /* 該指針指向的結構用於對codec的控制,通常和read,write字段聯合使用 */
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enum snd_soc_control_type control_type;/* 可以是SND_SOC_SPI,SND_SOC_I2C,SND_SOC_REGMAP中的一種 */
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unsigned int (*read)(struct snd_soc_codec *, unsigned int); /* 讀取Codec寄存器的函數 */
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int (*write)(struct snd_soc_codec *, unsigned int, unsigned int); /* 寫入Codec寄存器的函數 */
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/* dapm */
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struct snd_soc_dapm_context dapm; /* 用於DAPM控件 */
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};
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/* codec driver */
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struct snd_soc_codec_driver {
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/* driver ops */
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int (*probe)(struct snd_soc_codec *); /* codec驅動的probe函數,由snd_soc_instantiate_card回調 */
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int (*remove)(struct snd_soc_codec *);
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int (*suspend)(struct snd_soc_codec *); /* 電源管理 */
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int (*resume)(struct snd_soc_codec *); /* 電源管理 */
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/* Default control and setup, added after probe() is run */
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const struct snd_kcontrol_new *controls; /* 音頻控件指針 */
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const struct snd_soc_dapm_widget *dapm_widgets; /* dapm部件指針 */
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const struct snd_soc_dapm_route *dapm_routes; /* dapm路由指針 */
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/* codec wide operations */
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int (*set_sysclk)(...); /* 時鐘配置函數 */
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int (*set_pll)(...); /* 鎖相環配置函數 */
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/* codec IO */
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unsigned int (*read)(...); /* 讀取codec寄存器函數 */
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int (*write)(...); /* 寫入codec寄存器函數 */
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int (*volatile_register)(...); /* 用於判定某一寄存器是否是volatile */
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int (*readable_register)(...); /* 用於判定某一寄存器是否可讀 */
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int (*writable_register)(...); /* 用於判定某一寄存器是否可寫 */
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/* codec bias level */
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int (*set_bias_level)(...); /* 偏置電壓配置函數 */
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};
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/*
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* Digital Audio Interface runtime data.
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*
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* Holds runtime data for a DAI.
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*/
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struct snd_soc_dai {
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const char *name; /* dai的名字 */
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struct device *dev; /* 設備指針 */
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/* driver ops */
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struct snd_soc_dai_driver *driver; /* 指向dai驅動結構的指針 */
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/* DAI runtime info */
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unsigned int capture_active:1; /* stream is in use */
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unsigned int playback_active:1; /* stream is in use */
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/* DAI DMA data */
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void *playback_dma_data; /* 用於管理playback dma */
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void *capture_dma_data; /* 用於管理capture dma */
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/* parent platform/codec */
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union {
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struct snd_soc_platform *platform; /* 如果是cpu dai,指向所綁定的平臺 */
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struct snd_soc_codec *codec; /* 如果是codec dai指向所綁定的codec */
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};
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struct snd_soc_card *card; /* 指向Machine驅動中的crad實例 */
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};
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/*
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* Digital Audio Interface Driver.
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*
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* Describes the Digital Audio Interface in terms of its ALSA, DAI and AC97
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* operations and capabilities. Codec and platform drivers will register this
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* structure for every DAI they have.
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*
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* This structure covers the clocking, formating and ALSA operations for each
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* interface.
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*/
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struct snd_soc_dai_driver {
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/* DAI description */
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const char *name; /* dai驅動名字 */
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/* DAI driver callbacks */
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int (*probe)(struct snd_soc_dai *dai); /* dai驅動的probe函數,由snd_soc_instantiate_card回調 */
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int (*remove)(struct snd_soc_dai *dai);
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int (*suspend)(struct snd_soc_dai *dai); /* 電源管理 */
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int (*resume)(struct snd_soc_dai *dai);
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/* ops */
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const struct snd_soc_dai_ops *ops; /* 指向本dai的snd_soc_dai_ops結構 */
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/* DAI capabilities */
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struct snd_soc_pcm_stream capture; /* 描述capture的能力 */
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struct snd_soc_pcm_stream playback; /* 描述playback的能力 */
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};
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struct snd_soc_dai_ops {
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/*
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* DAI clocking configuration, all optional.
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* Called by soc_card drivers, normally in their hw_params.
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*/
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int (*set_sysclk)(...);
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int (*set_pll)(...);
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int (*set_clkdiv)(...);
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/*
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* DAI format configuration
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* Called by soc_card drivers, normally in their hw_params.
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*/
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int (*set_fmt)(...);
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int (*set_tdm_slot)(...);
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int (*set_channel_map)(...);
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int (*set_tristate)(...);
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/*
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* DAI digital mute - optional.
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* Called by soc-core to minimise any pops.
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*/
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int (*digital_mute)(...);
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/*
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* ALSA PCM audio operations - all optional.
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* Called by soc-core during audio PCM operations.
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*/
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int (*startup)(...);
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void (*shutdown)(...);
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int (*hw_params)(...);
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int (*hw_free)(...);
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int (*prepare)(...);
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int (*trigger)(...);
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/*
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* For hardware based FIFO caused delay reporting.
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* Optional.
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*/
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snd_pcm_sframes_t (*delay)(...);
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};
3. Codec的註冊
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static struct platform_driver wm8994_codec_driver = {
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.driver = {
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.name = "wm8994-codec",
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.owner = THIS_MODULE,
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},
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.probe = wm8994_probe,
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.remove = __devexit_p(wm8994_remove),
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};
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module_platform_driver(wm8994_codec_driver);
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static int __devinit wm8994_probe(struct platform_device *pdev)
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{
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return snd_soc_register_codec(&pdev->dev, &soc_codec_dev_wm8994,
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wm8994_dai, ARRAY_SIZE(wm8994_dai));
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}
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static struct snd_soc_codec_driver soc_codec_dev_wm8994 = {
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.probe = wm8994_codec_probe,
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.remove = wm8994_codec_remove,
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.suspend = wm8994_suspend,
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.resume = wm8994_resume,
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.set_bias_level = wm8994_set_bias_level,
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.reg_cache_size = WM8994_MAX_REGISTER,
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.volatile_register = wm8994_soc_volatile,
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};
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static struct snd_soc_dai_driver wm8994_dai[] = {
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{
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.name = "wm8994-aif1",
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.id = 1,
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.playback = {
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.stream_name = "AIF1 Playback",
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.channels_min = 1,
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.channels_max = 2,
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.rates = WM8994_RATES,
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.formats = WM8994_FORMATS,
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},
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.capture = {
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.stream_name = "AIF1 Capture",
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.channels_min = 1,
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.channels_max = 2,
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.rates = WM8994_RATES,
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.formats = WM8994_FORMATS,
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},
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.ops = &wm8994_aif1_dai_ops,
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},
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......
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}
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codec = kzalloc(sizeof(struct snd_soc_codec), GFP_KERNEL);
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/* create CODEC component name */
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codec->name = fmt_single_name(dev, &codec->id);
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codec->write = codec_drv->write;
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codec->read = codec_drv->read;
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codec->volatile_register = codec_drv->volatile_register;
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codec->readable_register = codec_drv->readable_register;
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codec->writable_register = codec_drv->writable_register;
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codec->dapm.bias_level = SND_SOC_BIAS_OFF;
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codec->dapm.dev = dev;
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codec->dapm.codec = codec;
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codec->dapm.seq_notifier = codec_drv->seq_notifier;
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codec->dapm.stream_event = codec_drv->stream_event;
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codec->dev = dev;
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codec->driver = codec_drv;
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codec->num_dai = num_dai;
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/* register any DAIs */
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if (num_dai) {
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ret = snd_soc_register_dais(dev, dai_drv, num_dai);
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if (ret < 0)
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goto fail;
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}
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list_add(&codec->list, &codec_list);
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snd_soc_instantiate_cards();
4. mfd設備
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static struct i2c_driver wm8994_i2c_driver = {
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.driver = {
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.name = "wm8994",
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.owner = THIS_MODULE,
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.pm = &wm8994_pm_ops,
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.of_match_table = wm8994_of_match,
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},
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.probe = wm8994_i2c_probe,
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.remove = wm8994_i2c_remove,
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.id_table = wm8994_i2c_id,
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};
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static int __init wm8994_i2c_init(void)
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{
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int ret;
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ret = i2c_add_driver(&wm8994_i2c_driver);
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if (ret != 0)
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pr_err("Failed to register wm8994 I2C driver: %d\n", ret);
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return ret;
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}
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module_init(wm8994_i2c_init);
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static int wm8994_i2c_probe(struct i2c_client *i2c,
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const struct i2c_device_id *id)
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{
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struct wm8994 *wm8994;
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int ret;
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wm8994 = devm_kzalloc(&i2c->dev, sizeof(struct wm8994), GFP_KERNEL);
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i2c_set_clientdata(i2c, wm8994);
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wm8994->dev = &i2c->dev;
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wm8994->irq = i2c->irq;
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wm8994->type = id->driver_data;
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wm8994->regmap = regmap_init_i2c(i2c, &wm8994_base_regmap_config);
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return wm8994_device_init(wm8994, i2c->irq);
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}
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/* Add the on-chip regulators first for bootstrapping */
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ret = mfd_add_devices(wm8994->dev, -1,
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wm8994_regulator_devs,
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ARRAY_SIZE(wm8994_regulator_devs),
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NULL, 0);
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if (pdata) {
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wm8994->irq_base = pdata->irq_base;
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wm8994->gpio_base = pdata->gpio_base;
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/* GPIO configuration is only applied if it's non-zero */
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......
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}
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wm8994_irq_init(wm8994);
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ret = mfd_add_devices(wm8994->dev, -1,
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wm8994_devs, ARRAY_SIZE(wm8994_devs),
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NULL, 0);
5. Codec初始化
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取出父設備的driver_data,其實就是上一節的wm8994結構變量,取出其中的regmap字段,複製到codec的control_data字段中;
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申請一個wm8994_priv私有數據結構,並把它設爲codec設備的driver_data;
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通過snd_soc_codec_set_cache_io初始化regmap io,完成這一步後,就可以使用API:snd_soc_read(),snd_soc_write()對codec的寄存器進行讀寫了;
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把父設備的driver_data(struct wm8994)和platform_data保存到私有結構wm8994_priv中;
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因爲要同時支持3個芯片型號,這裏要根據芯片的型號做一些特定的初始化工作;
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申請必要的幾個中斷;
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設置合適的偏置電平;
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通過snd_soc_update_bits修改某些寄存器;
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根據父設備的platform_data,完成特定於平臺的初始化配置;
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添加必要的control,dapm部件進而dapm路由信息;
5. regmap-io
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爲codec定義一個regmap_config結構實例,指定codec寄存器的地址和數據位等信息;
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根據codec的控制總線類型,調用以下其中一個函數,得到一個指向regmap結構的指針:
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struct regmap *regmap_init_i2c(struct i2c_client *i2c, const struct regmap_config *config);
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struct regmap *regmap_init_spi(struct spi_device *dev, const struct regmap_config *config);
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把獲得的regmap結構指針賦值給codec->control_data;
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調用soc-io的api:snd_soc_codec_set_cache_io使得soc-io和regmap進行關聯;