ALSA-DAPM

struct snd_kcontrol_new {
    snd_ctl_elem_iface_t iface; /* interface identifier */
    unsigned int device;        /* device/client number */
    unsigned int subdevice;     /* subdevice (substream) number */
    const unsigned char *name;  /* ASCII name of item */
    unsigned int index;     /* index of item */
    unsigned int access;        /* access rights */
    unsigned int count;     /* count of same elements */
    snd_kcontrol_info_t *info;
    snd_kcontrol_get_t *get;
    snd_kcontrol_put_t *put;
    union {
        snd_kcontrol_tlv_rw_t *c;
        const unsigned int *p;
    } tlv;
    unsigned long private_value;
};

/* dapm widget types */
enum snd_soc_dapm_type {
    snd_soc_dapm_input = 0,     /* input pin */
    snd_soc_dapm_output,        /* output pin */
    snd_soc_dapm_mux,           /* selects 1 analog signal from many inputs */
    snd_soc_dapm_virt_mux,          /* virtual version of snd_soc_dapm_mux */
    snd_soc_dapm_value_mux,         /* selects 1 analog signal from many inputs */
    snd_soc_dapm_mixer,         /* mixes several analog signals together */
    snd_soc_dapm_mixer_named_ctl,       /* mixer with named controls */
    snd_soc_dapm_pga,           /* programmable gain/attenuation (volume) */
    snd_soc_dapm_out_drv,           /* output driver */
    snd_soc_dapm_adc,           /* analog to digital converter */
    snd_soc_dapm_dac,           /* digital to analog converter */
    snd_soc_dapm_micbias,       /* microphone bias (power) */
    snd_soc_dapm_mic,           /* microphone */
    snd_soc_dapm_hp,            /* headphones */
    snd_soc_dapm_spk,           /* speaker */
    snd_soc_dapm_line,          /* line input/output */
    snd_soc_dapm_switch,        /* analog switch */
    snd_soc_dapm_vmid,          /* codec bias/vmid - to minimise pops */
    snd_soc_dapm_pre,           /* machine specific pre widget - exec first */
    snd_soc_dapm_post,          /* machine specific post widget - exec last */
    snd_soc_dapm_supply,        /* power/clock supply */
    snd_soc_dapm_regulator_supply,  /* external regulator */
    snd_soc_dapm_clock_supply,  /* external clock */
    snd_soc_dapm_aif_in,        /* audio interface input */
    snd_soc_dapm_aif_out,       /* audio interface output */
    snd_soc_dapm_siggen,        /* signal generator */
    snd_soc_dapm_dai_in,        /* link to DAI structure */
    snd_soc_dapm_dai_out,
    snd_soc_dapm_dai_link,      /* link between two DAI structures */
};

/* dapm widget */
struct snd_soc_dapm_widget {
    enum snd_soc_dapm_type id;   //该widget的类型值，比如snd_soc_dapm_output，snd_soc_dapm_mixer等等。
    const char *name;       /* widget name */
    const char *sname;  /* stream name */
    struct snd_soc_codec *codec;
    struct snd_soc_platform *platform;
    struct list_head list;		//所有注册到系统中的widget都会通过该list，链接到代表声卡的snd_soc_card结构的widgets链表头字段中
    struct snd_soc_dapm_context *dapm;	//snd_soc_dapm_context结构指针，ASoc把系统划分为多个dapm域，每个widget属于某个dapm域，同一个域代表着同样的偏置电压供电策略，
										//比如，同一个codec中的widget通常位于同一个dapm域，而平台上的widget可能又会位于另外一个platform域中。

    void *priv;             /* widget specific data */
    struct regulator *regulator;        /* attached regulator */	// 对于snd_soc_dapm_regulator_supply类型的widget，该字段指向与之相关的regulator结构指针。
    const struct snd_soc_pcm_stream *params; /* params for dai links */ //目前对于snd_soc_dapm_dai_link类型的widget，指向该dai的配置信息的snd_soc_pcm_stream结构

    /* dapm control */
    int reg;                /* negative reg = no direct dapm */
    unsigned char shift;            /* bits to shift */
    unsigned int value;             /* widget current value */
    unsigned int mask;          /* non-shifted mask */
    unsigned int on_val;            /* on state value */
    unsigned int off_val;           /* off state value */
    unsigned char power:1;          /* block power status */
    unsigned char invert:1;         /* invert the power bit */
    unsigned char active:1;         /* active stream on DAC, ADC's */
    unsigned char connected:1;      /* connected codec pin */
    unsigned char new:1;            /* cnew complete */
    unsigned char ext:1;            /* has external widgets */
    unsigned char force:1;          /* force state */
    unsigned char ignore_suspend:1;         /* kept enabled over suspend */
    unsigned char new_power:1;      /* power from this run */
    unsigned char power_checked:1;      /* power checked this run */
    int subseq;             /* sort within widget type */

    int (*power_check)(struct snd_soc_dapm_widget *w);

    /* external events */
    unsigned short event_flags;     /* flags to specify event types */
    int (*event)(struct snd_soc_dapm_widget*, struct snd_kcontrol *, int);

    /* kcontrols that relate to this widget */
    int num_kcontrols;
    const struct snd_kcontrol_new *kcontrol_news;
    struct snd_kcontrol **kcontrols;

    /* widget input and outputs */
    struct list_head sources;
    struct list_head sinks;

    /* used during DAPM updates */
    struct list_head power_list;
    struct list_head dirty;
    int inputs;			//该widget的所有有效路径中，连接到输入端的路径数量。
    int outputs;		//该widget的所有有效路径中，连接到输出端的路径数量。

    struct clk *clk;
};