ALSA driver---DAPM flow
参考：
https://elixir.bootlin.com/linux/v4.9.218/source/sound/soc/soc-dapm.c#L804
https://blog.csdn.net/DroidPhone/article/details/14146319
https://blog.csdn.net/DroidPhone/article/details/14052861
https://blog.csdn.net/whshiyun/article/details/80889838
定义widget
There are 4 power domains within DAPM:
- Codec domain – VREF, VMID (core codec and audio power). Usually controlled at codec probe/remove and suspend/resume, although can be set at stream time if power is not needed for sidetone, etc.
- Platform/Machine domain – physically connected inputs and outputs. Is platform/machine and user action specific, is configured by the machine driver and responds to asynchronous events. e.g when HP are inserted
- Path domain – audio subsystem signal paths. Automatically set when mixer and mux settings are changed by the user. e.g. alsamixer, amixer.
- Stream domain – DAC's and ADC's. Enabled and disabled when stream playback/capture is started and stopped respectively. e.g. aplay, arecord.
DAPM框架为我们提供了大量的辅助宏用来定义各种各样的widget控件.
widget 结构体如下：
* dapm widget */ struct snd_soc_dapm_widget { enum snd_soc_dapm_type id; const char *name; /* widget name */ const char *sname; /* stream name */ struct list_head list; struct snd_soc_dapm_context *dapm; void *priv; /* widget specific data */ struct regulator *regulator; /* attached regulator */ const struct snd_soc_pcm_stream *params; /* params for dai links */ unsigned int num_params; /* number of params for dai links */ unsigned int params_select; /* currently selected param for dai link */ /* dapm control */ int reg; /* negative reg = no direct dapm */ unsigned char shift; /* bits to shift */ 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 active:1; /* active stream on DAC, ADC's */ unsigned char connected:1; /* connected codec pin */ unsigned char new:1; /* cnew complete */ 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 */ unsigned char is_supply:1; /* Widget is a supply type widget */ unsigned char is_ep:2; /* Widget is a endpoint type widget */ 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; struct snd_soc_dobj dobj; /* widget input and output edges */ struct list_head edges[2]; /* used during DAPM updates */ struct list_head work_list; struct list_head power_list; struct list_head dirty; int endpoints[2]; struct clk *clk; };
widget的type:
/* 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_demux, /* connects the input to one of multiple outputs */ 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) - DEPRECATED: use snd_soc_dapm_supply */ 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_sink, snd_soc_dapm_dai_in, /* link to DAI structure */ snd_soc_dapm_dai_out, snd_soc_dapm_dai_link, /* link between two DAI structures */ snd_soc_dapm_kcontrol, /* Auto-disabled kcontrol */ };
codec domain:
/* codec domain */ #define SND_SOC_DAPM_VMID(wname) \ { .id = snd_soc_dapm_vmid, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0}
platform domain:
platform domain的widget分别对应信号发生器，输入引脚，输出引脚，麦克风，耳机，扬声器，线路输入接口。其中的reg字段被设置为SND_SOC_NOPM（-1），表明这些widget是没有寄存器控制位来控制widget的电源状态的。麦克风，耳机，扬声器，线路输入接口这几种widget，还可以定义一个dapm事件回调函数wevent，从event_flags字段的设置可以看出，他们只会响应SND_SOC_DAPM_POST_PMU（上电后）和SND_SOC_DAPM_PMD（下电前）事件，这几个widget通常会在machine驱动中定义，而SND_SOC_DAPM_INPUT和SND_SOC_DAPM_OUTPUT则用来定义codec芯片的输出输入脚，通常在codec驱动中定义，最后，在machine驱动中增加相应的route，把麦克风和耳机等widget与相应的codec输入输出引脚的widget连接起来。
/* platform domain */ #define SND_SOC_DAPM_SIGGEN(wname) \ { .id = snd_soc_dapm_siggen, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM } #define SND_SOC_DAPM_SINK(wname) \ { .id = snd_soc_dapm_sink, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM } #define SND_SOC_DAPM_INPUT(wname) \ { .id = snd_soc_dapm_input, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM } #define SND_SOC_DAPM_OUTPUT(wname) \ { .id = snd_soc_dapm_output, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM } #define SND_SOC_DAPM_MIC(wname, wevent) \ { .id = snd_soc_dapm_mic, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM, .event = wevent, \ .event_flags = SND_SOC_DAPM_PRE_PMU | SND_SOC_DAPM_POST_PMD} #define SND_SOC_DAPM_HP(wname, wevent) \ { .id = snd_soc_dapm_hp, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM, .event = wevent, \ .event_flags = SND_SOC_DAPM_POST_PMU | SND_SOC_DAPM_PRE_PMD} #define SND_SOC_DAPM_SPK(wname, wevent) \ { .id = snd_soc_dapm_spk, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM, .event = wevent, \ .event_flags = SND_SOC_DAPM_POST_PMU | SND_SOC_DAPM_PRE_PMD} #define SND_SOC_DAPM_LINE(wname, wevent) \ { .id = snd_soc_dapm_line, .name = wname, .kcontrol_news = NULL, \ .num_kcontrols = 0, .reg = SND_SOC_NOPM, .event = wevent, \ .event_flags = SND_SOC_DAPM_POST_PMU | SND_SOC_DAPM_PRE_PMD}
path domain:
path domain 的widget通常是对普通kcontrols控件的再封装，增加音频路径和电源管理功能，所以这种widget会包含一个或多个kcontrol，这些widget的reg和shift字段是需要赋值的，说明这些widget是有相应的电源控制寄存器的，DAPM框架在扫描和更新音频路径时，会利用这些寄存器来控制widget的电源状态，使得它们的供电状态是按需分配的，需要的时候（在有效的音频路径上）上电，不需要的时候（不再有效的音频路径上）下电。
#define SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert) \ .reg = wreg, .mask = 1, .shift = wshift, \ .on_val = winvert ? 0 : 1, .off_val = winvert ? 1 : 0 /* path domain */ #define SND_SOC_DAPM_PGA(wname, wreg, wshift, winvert,\ wcontrols, wncontrols) \ { .id = snd_soc_dapm_pga, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = wncontrols} #define SND_SOC_DAPM_OUT_DRV(wname, wreg, wshift, winvert,\ wcontrols, wncontrols) \ { .id = snd_soc_dapm_out_drv, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = wncontrols} #define SND_SOC_DAPM_MIXER(wname, wreg, wshift, winvert, \ wcontrols, wncontrols)\ { .id = snd_soc_dapm_mixer, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = wncontrols} #define SND_SOC_DAPM_MIXER_NAMED_CTL(wname, wreg, wshift, winvert, \ wcontrols, wncontrols)\ { .id = snd_soc_dapm_mixer_named_ctl, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = wncontrols} /* DEPRECATED: use SND_SOC_DAPM_SUPPLY */ #define SND_SOC_DAPM_MICBIAS(wname, wreg, wshift, winvert) \ { .id = snd_soc_dapm_micbias, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = NULL, .num_kcontrols = 0} #define SND_SOC_DAPM_SWITCH(wname, wreg, wshift, winvert, wcontrols) \ { .id = snd_soc_dapm_switch, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = 1} #define SND_SOC_DAPM_MUX(wname, wreg, wshift, winvert, wcontrols) \ { .id = snd_soc_dapm_mux, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = 1} #define SND_SOC_DAPM_DEMUX(wname, wreg, wshift, winvert, wcontrols) \ { .id = snd_soc_dapm_demux, .name = wname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .kcontrol_news = wcontrols, .num_kcontrols = 1}
这些widget需要完成和的mixer、mux等控件同样的功能，实际上，这是通过它们包含的kcontrol控件来完成的，这些kcontrol我们需要在定义widget前先定义好，然后通过wcontrols和num_kcontrols参数传递给这些辅助定义宏。dapm利用这些kcontrol完成音频路径的控制。不过，对于widget来说，它的任务还不止这些，dapm还要动态地管理这些音频路径的连结关系，以便可以根据这些连接关系来控制这些widget的电源状态，如果按照普通的方法定义这些kcontrol，是无法达到这个目的的，因此，dapm为我们提供了另外一套定义宏，由它们完成这些被widget包含的kcontrol的定义。
/* dapm kcontrol types */ #define SOC_DAPM_SINGLE(xname, reg, shift, max, invert) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \ .info = snd_soc_info_volsw, \ .get = snd_soc_dapm_get_volsw, .put = snd_soc_dapm_put_volsw, \ .private_value = SOC_SINGLE_VALUE(reg, shift, max, invert, 0) } #define SOC_DAPM_SINGLE_AUTODISABLE(xname, reg, shift, max, invert) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \ .info = snd_soc_info_volsw, \ .get = snd_soc_dapm_get_volsw, .put = snd_soc_dapm_put_volsw, \ .private_value = SOC_SINGLE_VALUE(reg, shift, max, invert, 1) } #define SOC_DAPM_SINGLE_VIRT(xname, max) \ SOC_DAPM_SINGLE(xname, SND_SOC_NOPM, 0, max, 0) #define SOC_DAPM_SINGLE_TLV(xname, reg, shift, max, invert, tlv_array) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \ .info = snd_soc_info_volsw, \ .access = SNDRV_CTL_ELEM_ACCESS_TLV_READ | SNDRV_CTL_ELEM_ACCESS_READWRITE,\ .tlv.p = (tlv_array), \ .get = snd_soc_dapm_get_volsw, .put = snd_soc_dapm_put_volsw, \ .private_value = SOC_SINGLE_VALUE(reg, shift, max, invert, 0) } #define SOC_DAPM_SINGLE_TLV_AUTODISABLE(xname, reg, shift, max, invert, tlv_array) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \ .info = snd_soc_info_volsw, \ .access = SNDRV_CTL_ELEM_ACCESS_TLV_READ | SNDRV_CTL_ELEM_ACCESS_READWRITE,\ .tlv.p = (tlv_array), \ .get = snd_soc_dapm_get_volsw, .put = snd_soc_dapm_put_volsw, \ .private_value = SOC_SINGLE_VALUE(reg, shift, max, invert, 1) } #define SOC_DAPM_SINGLE_TLV_VIRT(xname, max, tlv_array) \ SOC_DAPM_SINGLE(xname, SND_SOC_NOPM, 0, max, 0, tlv_array) #define SOC_DAPM_ENUM(xname, xenum) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \ .info = snd_soc_info_enum_double, \ .get = snd_soc_dapm_get_enum_double, \ .put = snd_soc_dapm_put_enum_double, \ .private_value = (unsigned long)&xenum } #define SOC_DAPM_ENUM_EXT(xname, xenum, xget, xput) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \ .info = snd_soc_info_enum_double, \ .get = xget, \ .put = xput, \ .private_value = (unsigned long)&xenum } #define SOC_DAPM_PIN_SWITCH(xname) \ { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname " Switch", \ .info = snd_soc_dapm_info_pin_switch, \ .get = snd_soc_dapm_get_pin_switch, \ .put = snd_soc_dapm_put_pin_switch, \ .private_value = (unsigned long)xname }
可以看出，SOC_DAPM_SINGLE对应与普通控件的SOC_SINGLE，SOC_DAPM_SINGLE_TLV对应SOC_SINGLE_TLV......，相比普通的kcontrol控件，dapm的kcontrol控件只是把info，get，put回调函数换掉了。dapm kcontrol的put回调函数不仅仅会更新控件本身的状态，他还会把这种变化传递到相邻的dapm kcontrol，相邻的dapm kcontrol又会传递这个变化到他自己相邻的dapm kcontrol，直到音频路径的末端，通过这种机制，只要改变其中一个widget的连接状态，与之相关的所有widget都会被扫描并测试一下自身是否还在有效的音频路径中，从而可以动态地改变自身的电源状态，这就是dapm的精髓所在。
stream domain:
这些widget主要包含音频输入/输出接口，ADC/DAC等等：
/* stream domain */ #define SND_SOC_DAPM_AIF_IN(wname, stname, wslot, wreg, wshift, winvert) \ { .id = snd_soc_dapm_aif_in, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), } #define SND_SOC_DAPM_AIF_IN_E(wname, stname, wslot, wreg, wshift, winvert, \ wevent, wflags) \ { .id = snd_soc_dapm_aif_in, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .event = wevent, .event_flags = wflags } #define SND_SOC_DAPM_AIF_OUT(wname, stname, wslot, wreg, wshift, winvert) \ { .id = snd_soc_dapm_aif_out, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), } #define SND_SOC_DAPM_AIF_OUT_E(wname, stname, wslot, wreg, wshift, winvert, \ wevent, wflags) \ { .id = snd_soc_dapm_aif_out, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .event = wevent, .event_flags = wflags } #define SND_SOC_DAPM_DAC(wname, stname, wreg, wshift, winvert) \ { .id = snd_soc_dapm_dac, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert) } #define SND_SOC_DAPM_DAC_E(wname, stname, wreg, wshift, winvert, \ wevent, wflags) \ { .id = snd_soc_dapm_dac, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .event = wevent, .event_flags = wflags} #define SND_SOC_DAPM_ADC(wname, stname, wreg, wshift, winvert) \ { .id = snd_soc_dapm_adc, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), } #define SND_SOC_DAPM_ADC_E(wname, stname, wreg, wshift, winvert, \ wevent, wflags) \ { .id = snd_soc_dapm_adc, .name = wname, .sname = stname, \ SND_SOC_DAPM_INIT_REG_VAL(wreg, wshift, winvert), \ .event = wevent, .event_flags = wflags} #define SND_SOC_DAPM_CLOCK_SUPPLY(wname) \ { .id = snd_soc_dapm_clock_supply, .name = wname, \ .reg = SND_SOC_NOPM, .event = dapm_clock_event, \ .event_flags = SND_SOC_DAPM_PRE_PMU | SND_SOC_DAPM_POST_PMD }
定义route
route 表示widget的连接路径(Destination Widget <=== Path Name <=== Source Widget)。route结构体如下:
/* * DAPM audio route definition. * * Defines an audio route originating at source via control and finishing * at sink. */ struct snd_soc_dapm_route { const char *sink; const char *control; const char *source; /* Note: currently only supported for links where source is a supply */ int (*connected)(struct snd_soc_dapm_widget *source, struct snd_soc_dapm_widget *sink); };
以sound/soc/codecs/tlv320aic23.c 为例，以下是tlv320 codec driver定义的widget定义的widgets和route
DAPM Widgets:
static const struct snd_soc_dapm_widget tlv320aic23_dapm_widgets[] = {
SND_SOC_DAPM_DAC("DAC", "Playback", TLV320AIC23_PWR, 3, 1),
SND_SOC_DAPM_ADC("ADC", "Capture", TLV320AIC23_PWR, 2, 1),
SND_SOC_DAPM_MUX("Capture Source", SND_SOC_NOPM, 0, 0,
&tlv320aic23_rec_src_mux_controls),
SND_SOC_DAPM_MIXER("Output Mixer", TLV320AIC23_PWR, 4, 1,
&tlv320aic23_output_mixer_controls[0],
ARRAY_SIZE(tlv320aic23_output_mixer_controls)),
SND_SOC_DAPM_PGA("Line Input", TLV320AIC23_PWR, 0, 1, NULL, 0),
SND_SOC_DAPM_PGA("Mic Input", TLV320AIC23_PWR, 1, 1, NULL, 0),
SND_SOC_DAPM_OUTPUT("LHPOUT"),
SND_SOC_DAPM_OUTPUT("RHPOUT"),
SND_SOC_DAPM_OUTPUT("LOUT"),
SND_SOC_DAPM_OUTPUT("ROUT"),
SND_SOC_DAPM_INPUT("LLINEIN"),
SND_SOC_DAPM_INPUT("RLINEIN"),
SND_SOC_DAPM_INPUT("MICIN"),
};
widget kcontrol:
/* PGA Mixer controls for Line and Mic switch */ static const struct snd_kcontrol_new tlv320aic23_output_mixer_controls[] = { SOC_DAPM_SINGLE("Line Bypass Switch", TLV320AIC23_ANLG, 3, 1, 0), SOC_DAPM_SINGLE("Mic Sidetone Switch", TLV320AIC23_ANLG, 5, 1, 0), SOC_DAPM_SINGLE("Playback Switch", TLV320AIC23_ANLG, 4, 1, 0), };
DAPM routes:
static const struct snd_soc_dapm_route tlv320aic23_intercon[] = {
/* Output Mixer */
{"Output Mixer", "Line Bypass Switch", "Line Input"},
{"Output Mixer", "Playback Switch", "DAC"},
{"Output Mixer", "Mic Sidetone Switch", "Mic Input"},
/* Outputs */
{"RHPOUT", NULL, "Output Mixer"},
{"LHPOUT", NULL, "Output Mixer"},
{"LOUT", NULL, "Output Mixer"},
{"ROUT", NULL, "Output Mixer"},
/* Inputs */
{"Line Input", "NULL", "LLINEIN"},
{"Line Input", "NULL", "RLINEIN"},
{"Mic Input", "NULL", "MICIN"},
/* input mux */
{"Capture Source", "Line", "Line Input"},
{"Capture Source", "Mic", "Mic Input"},
{"ADC", NULL, "Capture Source"},
};
capture audio path:
LLININ->Line Input->Catpture source ->ADC
MICIN->Mic Input->Catpute source->ADC
playback audio path:
DAC->Ouptput Mixer->LOUT/LHPOUT/ROUT/RHPOUT
LLININ->Line Input->Output Mixer->LOUT
MICIN->Mic Input ->Output Mixer->LOUT/LHPOUT/ROUT/RHPOUT
创建widget和path:
DAPM widget和route定义在CPU DAI driver和Codec driver的component driver.当调用snd_soc_register_component()注册CPU DAI ， 调用snd_soc_register_codec()注册Codec时，都会创建snd_soc_component类型的component, 并调用snd_soc_component_initialize()将component driver中定义的widgets和route赋值给component。
在snd_soc_instantiate_card()会调用soc_probe_link_component()->soc_probe_component()来probe component.
static int soc_probe_component(struct snd_soc_card *card, struct snd_soc_component *component) { struct snd_soc_dapm_context *dapm = snd_soc_component_get_dapm(component); struct snd_soc_dai *dai; int ret; if (!strcmp(component->name, "snd-soc-dummy")) return 0; if (component->card) { if (component->card != card) { dev_err(component->dev, "Trying to bind component to card \"%s\" but is already bound to card \"%s\"\n", card->name, component->card->name); return -ENODEV; } return 0; } if (!try_module_get(component->dev->driver->owner)) return -ENODEV; component->card = card; dapm->card = card; soc_set_name_prefix(card, component); soc_init_component_debugfs(component); if (component->dapm_widgets) { ret = snd_soc_dapm_new_controls(dapm, component->dapm_widgets, component->num_dapm_widgets); if (ret != 0) { dev_err(component->dev, "Failed to create new controls %d\n", ret); goto err_probe; } } list_for_each_entry(dai, &component->dai_list, list) { ret = snd_soc_dapm_new_dai_widgets(dapm, dai); if (ret != 0) { dev_err(component->dev, "Failed to create DAI widgets %d\n", ret); goto err_probe; } } if (component->probe) { ret = component->probe(component); if (ret < 0) { dev_err(component->dev, "ASoC: failed to probe component %d\n", ret); goto err_probe; } WARN(dapm->idle_bias_off && dapm->bias_level != SND_SOC_BIAS_OFF, "codec %s can not start from non-off bias with idle_bias_off==1\n", component->name); } /* machine specific init */ if (component->init) { ret = component->init(component); if (ret < 0) { dev_err(component->dev, "Failed to do machine specific init %d\n", ret); goto err_probe; } } if (component->controls) snd_soc_add_component_controls(component, component->controls, component->num_controls); if (component->dapm_routes) snd_soc_dapm_add_routes(dapm, component->dapm_routes, component->num_dapm_routes); list_add(&dapm->list, &card->dapm_list); /* This is a HACK and will be removed soon */ if (component->codec) list_add(&component->codec->card_list, &card->codec_dev_list); return 0; err_probe: soc_cleanup_component_debugfs(component); component->card = NULL; module_put(component->dev->driver->owner); return ret; }
在soc_probe_component()里面，
调用snd_soc_dapm_new_controls()对component->dapm_widgets中每个widget创建新的widget,将widget加到card->widgets链表中。该函数只是简单的一个循环，为传入的widget模板数组依次调用snd_soc_dapm_new_control函数，实际的工作由snd_soc_dapm_new_control完成
/** * snd_soc_dapm_new_controls - create new dapm controls * @dapm: DAPM context * @widget: widget array * @num: number of widgets * * Creates new DAPM controls based upon the templates. * * Returns 0 for success else error. */ int snd_soc_dapm_new_controls(struct snd_soc_dapm_context *dapm, const struct snd_soc_dapm_widget *widget, int num) { struct snd_soc_dapm_widget *w; int i; int ret = 0; mutex_lock_nested(&dapm->card->dapm_mutex, SND_SOC_DAPM_CLASS_INIT); for (i = 0; i < num; i++) { w = snd_soc_dapm_new_control_unlocked(dapm, widget); if (IS_ERR(w)) { ret = PTR_ERR(w); /* Do not nag about probe deferrals */ if (ret == -EPROBE_DEFER) break; dev_err(dapm->dev, "ASoC: Failed to create DAPM control %s (%d)\n", widget->name, ret); break; } if (!w) { dev_err(dapm->dev, "ASoC: Failed to create DAPM control %s\n", widget->name); ret = -ENOMEM; break; } widget++; } mutex_unlock(&dapm->card->dapm_mutex); return ret; }
创建widget由snd_soc_dapm_new_control_unlocked()完成,在此函数中调用dapm_cnew_widget()对widget分配内存,设定widget的power_check()函数(为不同类型的widget设置合适的power_check电源状态回调函数, 当音频路径发生变化时，power_check回调会被调用，用于检查该widget的电源状态是否需要更新)，最后将创建的widget加到card->widget链表中。
struct snd_soc_dapm_widget * snd_soc_dapm_new_control_unlocked(struct snd_soc_dapm_context *dapm, const struct snd_soc_dapm_widget *widget) { enum snd_soc_dapm_direction dir; struct snd_soc_dapm_widget *w; const char *prefix; int ret; if ((w = dapm_cnew_widget(widget)) == NULL) return NULL; switch (w->id) { case snd_soc_dapm_regulator_supply: w->regulator = devm_regulator_get(dapm->dev, w->name); if (IS_ERR(w->regulator)) { ret = PTR_ERR(w->regulator); if (ret == -EPROBE_DEFER) return ERR_PTR(ret); dev_err(dapm->dev, "ASoC: Failed to request %s: %d\n", w->name, ret); return NULL; } if (w->on_val & SND_SOC_DAPM_REGULATOR_BYPASS) { ret = regulator_allow_bypass(w->regulator, true); if (ret != 0) dev_warn(w->dapm->dev, "ASoC: Failed to bypass %s: %d\n", w->name, ret); } break; case snd_soc_dapm_clock_supply: #ifdef CONFIG_CLKDEV_LOOKUP w->clk = devm_clk_get(dapm->dev, w->name); if (IS_ERR(w->clk)) { ret = PTR_ERR(w->clk); if (ret == -EPROBE_DEFER) return ERR_PTR(ret); dev_err(dapm->dev, "ASoC: Failed to request %s: %d\n", w->name, ret); return NULL; } #else return NULL; #endif break; default: break; } prefix = soc_dapm_prefix(dapm); if (prefix) w->name = kasprintf(GFP_KERNEL, "%s %s", prefix, widget->name); else w->name = kstrdup_const(widget->name, GFP_KERNEL); if (w->name == NULL) { kfree(w); return NULL; } switch (w->id) { case snd_soc_dapm_mic: w->is_ep = SND_SOC_DAPM_EP_SOURCE; w->power_check = dapm_generic_check_power; break; case snd_soc_dapm_input: if (!dapm->card->fully_routed) w->is_ep = SND_SOC_DAPM_EP_SOURCE; w->power_check = dapm_generic_check_power; break; case snd_soc_dapm_spk: case snd_soc_dapm_hp: w->is_ep = SND_SOC_DAPM_EP_SINK; w->power_check = dapm_generic_check_power; break; case snd_soc_dapm_output: if (!dapm->card->fully_routed) w->is_ep = SND_SOC_DAPM_EP_SINK; w->power_check = dapm_generic_check_power; break; case snd_soc_dapm_vmid: case snd_soc_dapm_siggen: w->is_ep = SND_SOC_DAPM_EP_SOURCE; w->power_check = dapm_always_on_check_power; break; case snd_soc_dapm_sink: w->is_ep = SND_SOC_DAPM_EP_SINK; w->power_check = dapm_always_on_check_power; break; case snd_soc_dapm_mux: case snd_soc_dapm_demux: case snd_soc_dapm_switch: case snd_soc_dapm_mixer: case snd_soc_dapm_mixer_named_ctl: case snd_soc_dapm_adc: case snd_soc_dapm_aif_out: case snd_soc_dapm_dac: case snd_soc_dapm_aif_in: case snd_soc_dapm_pga: case snd_soc_dapm_out_drv: case snd_soc_dapm_micbias: case snd_soc_dapm_line: case snd_soc_dapm_dai_link: case snd_soc_dapm_dai_out: case snd_soc_dapm_dai_in: w->power_check = dapm_generic_check_power; break; case snd_soc_dapm_supply: case snd_soc_dapm_regulator_supply: case snd_soc_dapm_clock_supply: case snd_soc_dapm_kcontrol: w->is_supply = 1; w->power_check = dapm_supply_check_power; break; default: w->power_check = dapm_always_on_check_power; break; } w->dapm = dapm; INIT_LIST_HEAD(&w->list); INIT_LIST_HEAD(&w->dirty); list_add_tail(&w->list, &dapm->card->widgets); snd_soc_dapm_for_each_direction(dir) { INIT_LIST_HEAD(&w->edges[dir]); w->endpoints[dir] = -1; } /* machine layer sets up unconnected pins and insertions */ w->connected = 1; return w; }
基于component->dai_list中的dai 通过调用snd_soc_dapm_new_dai_widgets()创建dai widget，也将此widget加到card->widgets链表中。
在创建的widget中，其name和sname都是dai driver中的stream name，后面的链接时会去匹配这个名字.
int snd_soc_dapm_new_dai_widgets(struct snd_soc_dapm_context *dapm, struct snd_soc_dai *dai) { struct snd_soc_dapm_widget template; struct snd_soc_dapm_widget *w; WARN_ON(dapm->dev != dai->dev); memset(&template, 0, sizeof(template)); template.reg = SND_SOC_NOPM; if (dai->driver->playback.stream_name) { template.id = snd_soc_dapm_dai_in; template.name = dai->driver->playback.stream_name; template.sname = dai->driver->playback.stream_name; dev_dbg(dai->dev, "ASoC: adding %s widget\n", template.name); w = snd_soc_dapm_new_control_unlocked(dapm, &template); if (IS_ERR(w)) { int ret = PTR_ERR(w); /* Do not nag about probe deferrals */ if (ret != -EPROBE_DEFER) dev_err(dapm->dev, "ASoC: Failed to create %s widget (%d)\n", dai->driver->playback.stream_name, ret); return ret; } if (!w) { dev_err(dapm->dev, "ASoC: Failed to create %s widget\n", dai->driver->playback.stream_name); return -ENOMEM; } w->priv = dai; dai->playback_widget = w; } if (dai->driver->capture.stream_name) { template.id = snd_soc_dapm_dai_out; template.name = dai->driver->capture.stream_name; template.sname = dai->driver->capture.stream_name; dev_dbg(dai->dev, "ASoC: adding %s widget\n", template.name); w = snd_soc_dapm_new_control_unlocked(dapm, &template); if (IS_ERR(w)) { int ret = PTR_ERR(w); /* Do not nag about probe deferrals */ if (ret != -EPROBE_DEFER) dev_err(dapm->dev, "ASoC: Failed to create %s widget (%d)\n", dai->driver->playback.stream_name, ret); return ret; } if (!w) { dev_err(dapm->dev, "ASoC: Failed to create %s widget\n", dai->driver->capture.stream_name); return -ENOMEM; } w->priv = dai; dai->capture_widget = w; } return 0; }
基于component->dapm_routes创建dapm path,并将创建的path加到card->paths.
如果widget之间没有连接关系，dapm就无法实现动态的电源管理工作，正是widget之间有了连结关系，这些连接关系形成了一条所谓的完成的音频路径，dapm可以顺着这条路径，统一控制路径上所有widget的电源状态，widget之间是使用snd_soc_dapm_path结构进行连接的，驱动要做的是定义一个snd_soc_route结构数组，该数组的每个条目描述了目的widget的和源widget的名称，以及控制这个连接的kcontrol的名称，最终，驱动程序使用api函数snd_soc_dapm_add_routes来注册这些连接信息.
/** * snd_soc_dapm_add_routes - Add routes between DAPM widgets * @dapm: DAPM context * @route: audio routes * @num: number of routes * * Connects 2 dapm widgets together via a named audio path. The sink is * the widget receiving the audio signal, whilst the source is the sender * of the audio signal. * * Returns 0 for success else error. On error all resources can be freed * with a call to snd_soc_card_free(). */ int snd_soc_dapm_add_routes(struct snd_soc_dapm_context *dapm, const struct snd_soc_dapm_route *route, int num) { int i, r, ret = 0; mutex_lock_nested(&dapm->card->dapm_mutex, SND_SOC_DAPM_CLASS_INIT); for (i = 0; i < num; i++) { r = snd_soc_dapm_add_route(dapm, route); if (r < 0) { dev_err(dapm->dev, "ASoC: Failed to add route %s -> %s -> %s\n", route->source, route->control ? route->control : "direct", route->sink); ret = r; } route++; } mutex_unlock(&dapm->card->dapm_mutex); return ret; }
该函数只是一个循环，依次对参数传入的数组调用snd_soc_dapm_add_route，主要的工作由snd_soc_dapm_add_route完成。
static int snd_soc_dapm_add_route(struct snd_soc_dapm_context *dapm, const struct snd_soc_dapm_route *route) { struct snd_soc_dapm_widget *wsource = NULL, *wsink = NULL, *w; struct snd_soc_dapm_widget *wtsource = NULL, *wtsink = NULL; const char *sink; const char *source; char prefixed_sink[80]; char prefixed_source[80]; const char *prefix; int ret; prefix = soc_dapm_prefix(dapm); if (prefix) { snprintf(prefixed_sink, sizeof(prefixed_sink), "%s %s", prefix, route->sink); sink = prefixed_sink; snprintf(prefixed_source, sizeof(prefixed_source), "%s %s", prefix, route->source); source = prefixed_source; } else { sink = route->sink; source = route->source; } wsource = dapm_wcache_lookup(&dapm->path_source_cache, source); wsink = dapm_wcache_lookup(&dapm->path_sink_cache, sink); if (wsink && wsource) goto skip_search; /* * find src and dest widgets over all widgets but favor a widget from * current DAPM context */ list_for_each_entry(w, &dapm->card->widgets, list) { if (!wsink && !(strcmp(w->name, sink))) { wtsink = w; if (w->dapm == dapm) { wsink = w; if (wsource) break; } continue; } if (!wsource && !(strcmp(w->name, source))) { wtsource = w; if (w->dapm == dapm) { wsource = w; if (wsink) break; } } } /* use widget from another DAPM context if not found from this */ if (!wsink) wsink = wtsink; if (!wsource) wsource = wtsource; if (wsource == NULL) { dev_err(dapm->dev, "ASoC: no source widget found for %s\n", route->source); return -ENODEV; } if (wsink == NULL) { dev_err(dapm->dev, "ASoC: no sink widget found for %s\n", route->sink); return -ENODEV; } skip_search: dapm_wcache_update(&dapm->path_sink_cache, wsink); dapm_wcache_update(&dapm->path_source_cache, wsource); ret = snd_soc_dapm_add_path(dapm, wsource, wsink, route->control, route->connected); if (ret) goto err; return 0; err: dev_warn(dapm->dev, "ASoC: no dapm match for %s --> %s --> %s\n", source, route->control, sink); return ret; }
snd_soc_dapm_add_route()中用widget的名字来比较，遍历card->widgets链表，找出source widget和sink widget，最后调用snd_soc_dapm_add_path()来创建snd_soc_dapm_path结构体的path，将sourc widget和sink widget赋值给相应的成员，根据source 和sink widget的control(path name) 来初始化path->connect,如果有control，读取path->sink->kcontrol_new的register值来初始化path->connect,最后将path添加到card->paths链表。
static int snd_soc_dapm_add_path(struct snd_soc_dapm_context *dapm, struct snd_soc_dapm_widget *wsource, struct snd_soc_dapm_widget *wsink, const char *control, int (*connected)(struct snd_soc_dapm_widget *source, struct snd_soc_dapm_widget *sink)) { struct snd_soc_dapm_widget *widgets[2]; enum snd_soc_dapm_direction dir; struct snd_soc_dapm_path *path; int ret; if (wsink->is_supply && !wsource->is_supply) { dev_err(dapm->dev, "Connecting non-supply widget to supply widget is not supported (%s -> %s)\n", wsource->name, wsink->name); return -EINVAL; } if (connected && !wsource->is_supply) { dev_err(dapm->dev, "connected() callback only supported for supply widgets (%s -> %s)\n", wsource->name, wsink->name); return -EINVAL; } if (wsource->is_supply && control) { dev_err(dapm->dev, "Conditional paths are not supported for supply widgets (%s -> [%s] -> %s)\n", wsource->name, control, wsink->name); return -EINVAL; } ret = snd_soc_dapm_check_dynamic_path(dapm, wsource, wsink, control); if (ret) return ret; path = kzalloc(sizeof(struct snd_soc_dapm_path), GFP_KERNEL); if (!path) return -ENOMEM; path->node[SND_SOC_DAPM_DIR_IN] = wsource; path->node[SND_SOC_DAPM_DIR_OUT] = wsink; widgets[SND_SOC_DAPM_DIR_IN] = wsource; widgets[SND_SOC_DAPM_DIR_OUT] = wsink; path->connected = connected; INIT_LIST_HEAD(&path->list); INIT_LIST_HEAD(&path->list_kcontrol); if (wsource->is_supply || wsink->is_supply) path->is_supply = 1; /* connect static paths */ if (control == NULL) { path->connect = 1; } else { switch (wsource->id) { case snd_soc_dapm_demux: ret = dapm_connect_mux(dapm, path, control, wsource); if (ret) goto err; break; default: break; } switch (wsink->id) { case snd_soc_dapm_mux: ret = dapm_connect_mux(dapm, path, control, wsink); if (ret != 0) goto err; break; case snd_soc_dapm_switch: case snd_soc_dapm_mixer: case snd_soc_dapm_mixer_named_ctl: ret = dapm_connect_mixer(dapm, path, control); if (ret != 0) goto err; break; default: break; } } list_add(&path->list, &dapm->card->paths); snd_soc_dapm_for_each_direction(dir) list_add(&path->list_node[dir], &widgets[dir]->edges[dir]); snd_soc_dapm_for_each_direction(dir) { dapm_update_widget_flags(widgets[dir]); dapm_mark_dirty(widgets[dir], "Route added"); } if (dapm->card->instantiated && path->connect) dapm_path_invalidate(path); return 0; err: kfree(path); return ret; }
dapm_connect_mixer 用该函数连接一个sink widget为mixer类型的所有source端。
用需要用来连接的kcontrol的名字，和sink widget中的kcontrol模板数组中的名字相比较，path的名字设置为该kcontrol的名字，然后用dapm_set_path_status函数来初始化该输入端的连接状态。
/* connect mixer widget to its interconnecting audio paths */ static int dapm_connect_mixer(struct snd_soc_dapm_context *dapm, struct snd_soc_dapm_path *path, const char *control_name) { int i; /* search for mixer kcontrol */ for (i = 0; i < path->sink->num_kcontrols; i++) { if (!strcmp(control_name, path->sink->kcontrol_news[i].name)) { path->name = path->sink->kcontrol_news[i].name; dapm_set_mixer_path_status(path, i); return 0; } } return -ENODEV; }
以上是CPU DAI 和Codec内部widget建立path的过程。
在snd_soc_instantiate_card中，调用snd_soc_dapm_link_dai_widgets来建立dai widget和非dai widget(stream widget)的path
dai widget又分为cpu dai widget和codec dai widget.通常会为playback和capture各自创建一个dai widget，他们的类型分别是：
snd_soc_dapm_dai_in 对应playback dai
snd_soc_dapm_dai_out 对应capture dai
另外，dai widget的名字是使用stream name来命名的，他通常来自snd_soc_dai_driver中的stream_name字段。dai widget的sname字段也使用同样的名字。
stream widget stream widget通常是指那些要处理音频流数据的widget，它们包含以下这几种类型：
snd_soc_dapm_aif_in 用SND_SOC_DAPM_AIF_IN辅助宏定义
snd_soc_dapm_aif_out 用SND_SOC_DAPM_AIF_OUT辅助宏定义
snd_soc_dapm_dac 用SND_SOC_DAPM_DAC辅助宏定义
snd_soc_dapm_adc 用SND_SOC_DAPM_ADC辅助宏定义
比如：为以下codec dai建立名字叫做“Playback”和“Capture"的dai widget.
static struct snd_soc_dai_driver tlv320aic23_dai = { .name = "tlv320aic23-hifi", .playback = { .stream_name = "Playback", .channels_min = 2, .channels_max = 2, .rates = AIC23_RATES, .formats = AIC23_FORMATS,}, .capture = { .stream_name = "Capture", .channels_min = 2, .channels_max = 2, .rates = AIC23_RATES, .formats = AIC23_FORMATS,}, .ops = &tlv320aic23_dai_ops, };
“Playback”和“Capture"的dai widget将和如下stream widget建立path.
SND_SOC_DAPM_DAC("DAC", "Playback", TLV320AIC23_PWR, 3, 1), SND_SOC_DAPM_ADC("ADC", "Capture", TLV320AIC23_PWR, 2, 1),
snd_soc_dapm_link_dai_widgets函数会去遍历每一个dai widgets，然后遍历所有的非dai widgets (stream widget)，如果非dai widgets(stream widget)的stream name与dai widgets的name相同，则把两个widgets建立path。这也是为什么创建dai widgets时name一定要是stream name的原因之一了。
int snd_soc_dapm_link_dai_widgets(struct snd_soc_card *card) { struct snd_soc_dapm_widget *dai_w, *w; struct snd_soc_dapm_widget *src, *sink; struct snd_soc_dai *dai; /* For each DAI widget... */ list_for_each_entry(dai_w, &card->widgets, list) { switch (dai_w->id) { case snd_soc_dapm_dai_in: case snd_soc_dapm_dai_out: break; default: continue; } /* let users know there is no DAI to link */ if (!dai_w->priv) { dev_dbg(card->dev, "dai widget %s has no DAI\n", dai_w->name); continue; } dai = dai_w->priv; /* ...find all widgets with the same stream and link them */ list_for_each_entry(w, &card->widgets, list) { if (w->dapm != dai_w->dapm) continue; switch (w->id) { case snd_soc_dapm_dai_in: case snd_soc_dapm_dai_out: continue; default: break; } if (!w->sname || !strstr(w->sname, dai_w->sname)) continue; if (dai_w->id == snd_soc_dapm_dai_in) { src = dai_w; sink = w; } else { src = w; sink = dai_w; } dev_dbg(dai->dev, "%s -> %s\n", src->name, sink->name); snd_soc_dapm_add_path(w->dapm, src, sink, NULL, NULL); } } return 0; }
调用snd_soc_dapm_connect_dai_link_widgets() 建立CPU BE DAI widget 和 codec DAI widget之间的path.
void snd_soc_dapm_connect_dai_link_widgets(struct snd_soc_card *card) { struct snd_soc_pcm_runtime *rtd; /* for each BE DAI link... */ list_for_each_entry(rtd, &card->rtd_list, list) { /* * dynamic FE links have no fixed DAI mapping. * CODEC<->CODEC links have no direct connection. */ if (rtd->dai_link->dynamic || rtd->dai_link->params) continue; dapm_connect_dai_link_widgets(card, rtd); } } static void dapm_connect_dai_link_widgets(struct snd_soc_card *card, struct snd_soc_pcm_runtime *rtd) { struct snd_soc_dai *cpu_dai = rtd->cpu_dai; struct snd_soc_dapm_widget *sink, *source; int i; for (i = 0; i < rtd->num_codecs; i++) { struct snd_soc_dai *codec_dai = rtd->codec_dais[i]; /* connect BE DAI playback if widgets are valid */ if (codec_dai->playback_widget && cpu_dai->playback_widget) { source = cpu_dai->playback_widget; sink = codec_dai->playback_widget; dev_dbg(rtd->dev, "connected DAI link %s:%s -> %s:%s\n", cpu_dai->component->name, source->name, codec_dai->component->name, sink->name); snd_soc_dapm_add_path(&card->dapm, source, sink, NULL, NULL); } /* connect BE DAI capture if widgets are valid */ if (codec_dai->capture_widget && cpu_dai->capture_widget) { source = codec_dai->capture_widget; sink = cpu_dai->capture_widget; dev_dbg(rtd->dev, "connected DAI link %s:%s -> %s:%s\n", codec_dai->component->name, source->name, cpu_dai->component->name, sink->name); snd_soc_dapm_add_path(&card->dapm, source, sink, NULL, NULL); } } }
建立widget 的dapm kcontrol
定义一个widget，我们需要指定两个很重要的内容：一个是用于控制widget的电源状态的reg/shift等寄存器信息，另一个是用于控制音频路径切换的dapm kcontrol信息，这些dapm kcontrol有它们自己的reg/shift寄存器信息用于切换widget的路径连接方式。前面我们只是创建了widget的实例，并把它们注册到声卡的widgts链表中，但是到目前为止，包含在widget中的dapm kcontrol并没有建立起来，dapm框架在声卡的初始化阶段，等所有的widget（包括machine、platform、codec）都创建好之后，通过snd_soc_dapm_new_widgets函数，创建widget内包含的dapm kcontrol，并初始化widget的初始电源状态和音频路径的初始连接状态。
/** * snd_soc_dapm_new_widgets - add new dapm widgets * @card: card to be checked for new dapm widgets * * Checks the codec for any new dapm widgets and creates them if found. * * Returns 0 for success. */ int snd_soc_dapm_new_widgets(struct snd_soc_card *card) { struct snd_soc_dapm_widget *w; unsigned int val; mutex_lock_nested(&card->dapm_mutex, SND_SOC_DAPM_CLASS_INIT); list_for_each_entry(w, &card->widgets, list) { if (w->new) continue; if (w->num_kcontrols) { w->kcontrols = kzalloc(w->num_kcontrols * sizeof(struct snd_kcontrol *), GFP_KERNEL); if (!w->kcontrols) { mutex_unlock(&card->dapm_mutex); return -ENOMEM; } } switch(w->id) { case snd_soc_dapm_switch: case snd_soc_dapm_mixer: case snd_soc_dapm_mixer_named_ctl: dapm_new_mixer(w); break; case snd_soc_dapm_mux: case snd_soc_dapm_demux: dapm_new_mux(w); break; case snd_soc_dapm_pga: case snd_soc_dapm_out_drv: dapm_new_pga(w); break; case snd_soc_dapm_dai_link: dapm_new_dai_link(w); break; default: break; } /* Read the initial power state from the device */ if (w->reg >= 0) { soc_dapm_read(w->dapm, w->reg, &val); val = val >> w->shift; val &= w->mask; if (val == w->on_val) w->power = 1; } w->new = 1; dapm_mark_dirty(w, "new widget"); dapm_debugfs_add_widget(w); } dapm_power_widgets(card, SND_SOC_DAPM_STREAM_NOP); mutex_unlock(&card->dapm_mutex); return 0; }
该函数通过声卡的widgets链表，遍历所有已经注册了的widget，其中的new字段用于判断该widget是否已经执行过snd_soc_dapm_new_widgets函数，如果num_kcontrols字段有数值，表明该widget包含有若干个dapm kcontrol，那么就需要为这些kcontrol分配一个指针数组，并把数组的首地址赋值给widget的kcontrols字段，该数组存放着指向这些kcontrol的指针，当然现在这些都是空指针，因为实际的kcontrol现在还没有被创建.
接着，对几种能影响音频路径的widget，创建并初始化它们所包含的dapm kcontrol.
需要用到的创建函数分别是：
dapm_new_mixer() 对于mixer类型，用该函数创建dapm kcontrol；
dapm_new_mux() 对于mux类型，用该函数创建dapm kcontrol；
dapm_new_pga() 对于pga类型，用该函数创建dapm kcontrol；
根据widget寄存器的当前值，初始化widget的电源状态，并设置到power字段中.
接着，设置new字段，表明该widget已经初始化完成，我们还要吧该widget加入到声卡的dapm_dirty链表中，表明该widget的状态发生了变化，稍后在合适的时刻，dapm框架会扫描dapm_dirty链表，统一处理所有已经变化的widget。为什么要统一处理？因为dapm要控制各种widget的上下电顺序，同时也是为了减少寄存器的读写次数（多个widget可能使用同一个寄存器）
最后，通过dapm_power_widgets函数，统一处理所有位于dapm_dirty链表上的widget的状态改变.
damp_new_mixer:
/* create new dapm mixer control */ static int dapm_new_mixer(struct snd_soc_dapm_widget *w) { int i, ret; struct snd_soc_dapm_path *path; struct dapm_kcontrol_data *data; /* add kcontrol */ for (i = 0; i < w->num_kcontrols; i++) { /* match name */ snd_soc_dapm_widget_for_each_source_path(w, path) { /* mixer/mux paths name must match control name */ if (path->name != (char *)w->kcontrol_news[i].name) continue; if (!w->kcontrols[i]) { ret = dapm_create_or_share_kcontrol(w, i); if (ret < 0) return ret; } dapm_kcontrol_add_path(w->kcontrols[i], path); data = snd_kcontrol_chip(w->kcontrols[i]); if (data->widget) snd_soc_dapm_add_path(data->widget->dapm, data->widget, path->source, NULL, NULL); } } return 0; }
一个mixer类型的widget是由多个kcontrol组成的，每个kcontrol控制着mixer的一个输入端的开启和关闭，所以，该函数会根据kcontrol的数量做循环，逐个建立对应的kcontrol。
找到mixer widget的source path, 如果kcontrol的name和source path的name一样则创建kcontrol.
如果kcontrol之前没有被创建，则通过dapm_create_or_share_kcontrol()创建这个输入端的kcontrol.
/* * Determine if a kcontrol is shared. If it is, look it up. If it isn't, * create it. Either way, add the widget into the control's widget list */ static int dapm_create_or_share_kcontrol(struct snd_soc_dapm_widget *w, int kci) { struct snd_soc_dapm_context *dapm = w->dapm; struct snd_card *card = dapm->card->snd_card; const char *prefix; size_t prefix_len; int shared; struct snd_kcontrol *kcontrol; bool wname_in_long_name, kcname_in_long_name; char *long_name = NULL; const char *name; int ret = 0; prefix = soc_dapm_prefix(dapm); if (prefix) prefix_len = strlen(prefix) + 1; else prefix_len = 0; shared = dapm_is_shared_kcontrol(dapm, w, &w->kcontrol_news[kci], &kcontrol); if (!kcontrol) { if (shared) { wname_in_long_name = false; kcname_in_long_name = true; } else { switch (w->id) { case snd_soc_dapm_switch: case snd_soc_dapm_mixer: case snd_soc_dapm_pga: case snd_soc_dapm_out_drv: wname_in_long_name = true; kcname_in_long_name = true; break; case snd_soc_dapm_mixer_named_ctl: wname_in_long_name = false; kcname_in_long_name = true; break; case snd_soc_dapm_demux: case snd_soc_dapm_mux: wname_in_long_name = true; kcname_in_long_name = false; break; default: return -EINVAL; } } if (wname_in_long_name && kcname_in_long_name) { /* * The control will get a prefix from the control * creation process but we're also using the same * prefix for widgets so cut the prefix off the * front of the widget name. */ long_name = kasprintf(GFP_KERNEL, "%s %s", w->name + prefix_len, w->kcontrol_news[kci].name); if (long_name == NULL) return -ENOMEM; name = long_name; } else if (wname_in_long_name) { long_name = NULL; name = w->name + prefix_len; } else { long_name = NULL; name = w->kcontrol_news[kci].name; } kcontrol = snd_soc_cnew(&w->kcontrol_news[kci], NULL, name, prefix); if (!kcontrol) { ret = -ENOMEM; goto exit_free; } kcontrol->private_free = dapm_kcontrol_free; ret = dapm_kcontrol_data_alloc(w, kcontrol, name); if (ret) { snd_ctl_free_one(kcontrol); goto exit_free; } ret = snd_ctl_add(card, kcontrol); if (ret < 0) { dev_err(dapm->dev, "ASoC: failed to add widget %s dapm kcontrol %s: %d\n", w->name, name, ret); goto exit_free; } } ret = dapm_kcontrol_add_widget(kcontrol, w); if (ret == 0) w->kcontrols[kci] = kcontrol; exit_free: kfree(long_name); return ret; }
dapm_create_or_share_kcontrol()所做的事情如下：
（1） 为了节省内存，通过kcontrol名字的匹配查找，如果这个kcontrol已经在其他widget中已经创建好了，那我们不再创建，dapm_is_shared_kcontrol的参数kcontrol会返回已经创建好的kcontrol的指针。
（2） 如果kcontrol指针被赋值，说明在（1）中查找到了其他widget中同名的kcontrol，我们不用再次创建，只要共享该kcontrol即可。
（3） 在snd_soc_cnew()中调用标准的kcontrol创建函数snd_ctl_new1()。
（4） 在dapm_kcontrol_data_alloc中，如果widget支持autodisable特性，创建与该kcontrol所对应的影子widget，该影子widget的类型是：snd_soc_dapm_kcontrol。
（5） 调用snd_ctl_add()将创建的kcontrol添加到card->snd_card->controls链表
（6） 把所有共享该kcontrol的影子widget（snd_soc_dapm_kcontrol），加入到kcontrol的private_data字段所指向的dapm_kcontrol_data结构中。
（7） 把创建好的kcontrol指针赋值到widget的kcontrols数组中。
增加一个虚拟的影子widget，该影子widget在dapm_new_mixer()中和path->source widget建立path，因为使用了kcontrol本身的reg/shift等寄存器信息，所以实际上控制的是该kcontrol的开和关，这个影子widget只有在kcontrol的autodisable字段被设置的情况下才会被创建，该特性使得source的关闭时，与之连接的mixer的输入端也可以自动关闭。
在 snd_soc_dapm_new_widgets的最后，通过dapm_power_widgets()函数，统一处理所有位于dapm_dirty链表上的widget的状态改变.
/* * Scan each dapm widget for complete audio path. * A complete path is a route that has valid endpoints i.e.:- * * o DAC to output pin. * o Input pin to ADC. * o Input pin to Output pin (bypass, sidetone) * o DAC to ADC (loopback). */ static int dapm_power_widgets(struct snd_soc_card *card, int event) { struct snd_soc_dapm_widget *w; struct snd_soc_dapm_context *d; LIST_HEAD(up_list); LIST_HEAD(down_list); ASYNC_DOMAIN_EXCLUSIVE(async_domain); enum snd_soc_bias_level bias; lockdep_assert_held(&card->dapm_mutex); trace_snd_soc_dapm_start(card); list_for_each_entry(d, &card->dapm_list, list) { if (dapm_idle_bias_off(d)) d->target_bias_level = SND_SOC_BIAS_OFF; else d->target_bias_level = SND_SOC_BIAS_STANDBY; } dapm_reset(card); /* Check which widgets we need to power and store them in * lists indicating if they should be powered up or down. We * only check widgets that have been flagged as dirty but note * that new widgets may be added to the dirty list while we * iterate. */ list_for_each_entry(w, &card->dapm_dirty, dirty) { dapm_power_one_widget(w, &up_list, &down_list); } list_for_each_entry(w, &card->widgets, list) { switch (w->id) { case snd_soc_dapm_pre: case snd_soc_dapm_post: /* These widgets always need to be powered */ break; default: list_del_init(&w->dirty); break; } if (w->new_power) { d = w->dapm; /* Supplies and micbiases only bring the * context up to STANDBY as unless something * else is active and passing audio they * generally don't require full power. Signal * generators are virtual pins and have no * power impact themselves. */ switch (w->id) { case snd_soc_dapm_siggen: case snd_soc_dapm_vmid: break; case snd_soc_dapm_supply: case snd_soc_dapm_regulator_supply: case snd_soc_dapm_clock_supply: case snd_soc_dapm_micbias: if (d->target_bias_level < SND_SOC_BIAS_STANDBY) d->target_bias_level = SND_SOC_BIAS_STANDBY; break; default: d->target_bias_level = SND_SOC_BIAS_ON; break; } } } /* Force all contexts in the card to the same bias state if * they're not ground referenced. */ bias = SND_SOC_BIAS_OFF; list_for_each_entry(d, &card->dapm_list, list) if (d->target_bias_level > bias) bias = d->target_bias_level; list_for_each_entry(d, &card->dapm_list, list) if (!dapm_idle_bias_off(d)) d->target_bias_level = bias; trace_snd_soc_dapm_walk_done(card); /* Run card bias changes at first */ dapm_pre_sequence_async(&card->dapm, 0); /* Run other bias changes in parallel */ list_for_each_entry(d, &card->dapm_list, list) { if (d != &card->dapm) async_schedule_domain(dapm_pre_sequence_async, d, &async_domain); } async_synchronize_full_domain(&async_domain); list_for_each_entry(w, &down_list, power_list) { dapm_seq_check_event(card, w, SND_SOC_DAPM_WILL_PMD); } list_for_each_entry(w, &up_list, power_list) { dapm_seq_check_event(card, w, SND_SOC_DAPM_WILL_PMU); } /* Power down widgets first; try to avoid amplifying pops. */ dapm_seq_run(card, &down_list, event, false); dapm_widget_update(card); /* Now power up. */ dapm_seq_run(card, &up_list, event, true); /* Run all the bias changes in parallel */ list_for_each_entry(d, &card->dapm_list, list) { if (d != &card->dapm) async_schedule_domain(dapm_post_sequence_async, d, &async_domain); } async_synchronize_full_domain(&async_domain); /* Run card bias changes at last */ dapm_post_sequence_async(&card->dapm, 0); /* do we need to notify any clients that DAPM event is complete */ list_for_each_entry(d, &card->dapm_list, list) { if (d->stream_event) d->stream_event(d, event); } pop_dbg(card->dev, card->pop_time, "DAPM sequencing finished, waiting %dms\n", card->pop_time); pop_wait(card->pop_time); trace_snd_soc_dapm_done(card); return 0; }
dapm_power_widgets
当一个widget的状态改变后，该widget会被加入dapm_dirty链表，然后通过dapm_power_widgets函数来改变整个音频路径上的电源状态
1)该函数通过遍历dapm_dirty链表，对每个链表中的widget调用dapm_power_one_widget，dapm_power_one_widget函数除了处理自身的状态改变外，还把自身的变化传递到和它相连的邻居widget中，结果就是，所有需要上电的widget会被放在up_list链表中，而所有需要下电的widget会被放在down_list链表中，这个函数我们稍后再讨论。
2)遍历down_list链表，向其中的widget发出SND_SOC_DAPM_WILL_PMD事件，感兴趣该事件的widget的event回调会被调用。
3)遍历up_list链表，向其中的widget发出SND_SOC_DAPM_WILL_PMU事件，感兴趣该事件的widget的event回调会被调用。
4)通过dapm_seq_run函数，处理down_list中的widget，使它们按定义好的顺序依次下电。
5)通过dapm_widget_update函数，切换触发该次状态变化的widget的kcontrol中的寄存器值，对应的结果就是：改变音频路径。
6)通过dapm_seq_run函数，处理up_list中的widget，使它们按定义好的顺序依次上电。
7)对每个dapm context发出状态改变回调。
8)适当的延时，防止pop-pop声。
dapm_power_one_widget:
dapm_power_widgets的第一步，就是遍历dapm_dirty链表，对每个链表中的widget调用dapm_power_one_widget，把需要上电和需要下电的widget分别加入到up_list和down_list链表中，同时，他还会把受到影响的邻居widget再次加入到dapm_dirty链表的末尾，通过这个动作，声卡中所以受到影响的widget都会被“感染”，依次被加到dapm_dirty链表，然后依次被执行dapm_power_one_widget函数。
static void dapm_power_one_widget(struct snd_soc_dapm_widget *w, struct list_head *up_list, struct list_head *down_list) { int power; switch (w->id) { case snd_soc_dapm_pre: dapm_seq_insert(w, down_list, false); break; case snd_soc_dapm_post: dapm_seq_insert(w, up_list, true); break; default: power = dapm_widget_power_check(w); dapm_widget_set_power(w, power, up_list, down_list); break; } }
1)通过dapm_widget_power_check，调用widget的power_check回调函数，获得该widget新的电源状态。
2)调用dapm_widget_set_power，“感染”与之相连的邻居widget。
遍历source widget，通过dapm_widget_set_peer_power函数，把处于连接状态的source widget加入dapm_dirty链表中。
遍历sink widget，通过dapm_widget_set_peer_power函数，把处于连接状态的sink widget加入dapm_dirty链表中。
3)根据第一步得到的新的电源状态，把widget加入到up_list或down_list链表中。
可见，通过该函数，一个widget的状态改变，邻居widget会受到“感染”而被加入到dapm_dirty链表的末尾，所以扫描到链表的末尾时，邻居widget也会执行同样的操作，从而“感染”邻居的邻居，直到没有新的widget被加入dapm_dirty链表为止，这时，所有受到影响的widget都被加入到up_list或down_li链表中，等待后续的上下电操作。
power_check回调函数
在创建widget的时候，widget的power_check回调函数会根据widget的类型，设置不同的回调函数。当widget的状态改变后，dapm会遍历dapm_dirty链表，并通过power_check回调函数，决定该widget是否需要上电。
dapm要给一个widget上电的其中一个前提条件是：这个widget位于一条完整的音频路径上，而一条完整的音频路径的两头，必须是输入/输出引脚，或者是一个外部音频设备，又或者是一个处于激活状态的音频流widget，它们可以位于路径的末端，但不是构成完成音频路径的必要条件，我们只用它来判断扫描一条路径的结束条件。
大多数的widget的power_check回调被设置为：dapm_generic_check_power
/* Generic check to see if a widget should be powered. */ static int dapm_generic_check_power(struct snd_soc_dapm_widget *w) { int in, out; DAPM_UPDATE_STAT(w, power_checks); in = is_connected_input_ep(w, NULL, NULL); out = is_connected_output_ep(w, NULL, NULL); return out != 0 && in != 0; }
dapm_generic_check_power()中分别用is_connected_output_ep和is_connected_input_ep得到该widget连到多少个input endpoint和output endpoint, 从而判断是否有同时连接到一个输入端和一个输出端，如果是，返回1来表示该widget需要上电。
dapm提供了两个内部函数，用来统计一个widget连接到输出引脚、输入引脚、激活的音频流widget的有效路径个数：
is_connected_output_ep 返回连接至输出引脚或激活状态的输出音频流的路径数量
is_connected_input_ep 返回连接至输入引脚或激活状态的输入音频流的路径数量
/* * Recursively check for a completed path to an active or physically connected * output widget. Returns number of complete paths. * * Optionally, can be supplied with a function acting as a stopping condition. * This function takes the dapm widget currently being examined and the walk * direction as an arguments, it should return true if widgets from that point * in the graph onwards should not be added to the widget list. */ static int is_connected_output_ep(struct snd_soc_dapm_widget *widget, struct list_head *list, bool (*custom_stop_condition)(struct snd_soc_dapm_widget *i, enum snd_soc_dapm_direction)) { return is_connected_ep(widget, list, SND_SOC_DAPM_DIR_OUT, is_connected_output_ep, custom_stop_condition); } /* * Recursively check for a completed path to an active or physically connected * input widget. Returns number of complete paths. * * Optionally, can be supplied with a function acting as a stopping condition. * This function takes the dapm widget currently being examined and the walk * direction as an arguments, it should return true if the walk should be * stopped and false otherwise. */ static int is_connected_input_ep(struct snd_soc_dapm_widget *widget, struct list_head *list, bool (*custom_stop_condition)(struct snd_soc_dapm_widget *i, enum snd_soc_dapm_direction)) { return is_connected_ep(widget, list, SND_SOC_DAPM_DIR_IN, is_connected_input_ep, custom_stop_condition); }
/* * Common implementation for is_connected_output_ep() and * is_connected_input_ep(). The function is inlined since the combined size of * the two specialized functions is only marginally larger then the size of the * generic function and at the same time the fast path of the specialized * functions is significantly smaller than the generic function. */ static __always_inline int is_connected_ep(struct snd_soc_dapm_widget *widget, struct list_head *list, enum snd_soc_dapm_direction dir, int (*fn)(struct snd_soc_dapm_widget *, struct list_head *, bool (*custom_stop_condition)(struct snd_soc_dapm_widget *, enum snd_soc_dapm_direction)), bool (*custom_stop_condition)(struct snd_soc_dapm_widget *, enum snd_soc_dapm_direction)) { enum snd_soc_dapm_direction rdir = SND_SOC_DAPM_DIR_REVERSE(dir); struct snd_soc_dapm_path *path; int con = 0; if (widget->endpoints[dir] >= 0) return widget->endpoints[dir]; DAPM_UPDATE_STAT(widget, path_checks); /* do we need to add this widget to the list ? */ if (list) list_add_tail(&widget->work_list, list); if (custom_stop_condition && custom_stop_condition(widget, dir)) { list = NULL; custom_stop_condition = NULL; } if ((widget->is_ep & SND_SOC_DAPM_DIR_TO_EP(dir)) && widget->connected) { widget->endpoints[dir] = snd_soc_dapm_suspend_check(widget); return widget->endpoints[dir]; } snd_soc_dapm_widget_for_each_path(widget, rdir, path) { DAPM_UPDATE_STAT(widget, neighbour_checks); if (path->weak || path->is_supply) continue; if (path->walking) return 1; trace_snd_soc_dapm_path(widget, dir, path); if (path->connect) { path->walking = 1; con += fn(path->node[dir], list, custom_stop_condition); path->walking = 0; } } widget->endpoints[dir] = con; return con; }
dapm_seq_run
当所有需要上电或下电的widget都被加入到dapm_dirty链表后，接着会通过dapm_seq_run处理down_list链表上的widget，把该链表上的widget按顺序下电，然后通过dapm_widget_update更新widget中的kcontrol（这个kcontrol通常就是触发本次状态改变的触发源），接着又通过apm_seq_run处理up_list链表上的widget，把该链表上的widget按顺序上电。最终的上电或下电操作需要通过codec的寄存器来实现，因为定义widget时，如果这是一个带电源控制的widget，我们必须提供reg/shift等字段的设置值，如果该widget无需寄存器控制电源状态，则reg字段必须赋值为：
SND_SOC_NOPM (该宏定义的实际值是-1)
具体实现上，dapm框架使用了一点技巧：如果位于同一个上下电顺序的几个widget使用了同一个寄存器地址（一个寄存器可能使用不同的位来控制不同的widget的电源状态），dapm_seq_run通过dapm_seq_run_coalesced函数合并这几个widget的变更，然后只需要把合并后的值一次写入寄存器即可。
/* Apply a DAPM power sequence. * * We walk over a pre-sorted list of widgets to apply power to. In * order to minimise the number of writes to the device required * multiple widgets will be updated in a single write where possible. * Currently anything that requires more than a single write is not * handled. */ static void dapm_seq_run(struct snd_soc_card *card, struct list_head *list, int event, bool power_up) { struct snd_soc_dapm_widget *w, *n; struct snd_soc_dapm_context *d; LIST_HEAD(pending); int cur_sort = -1; int cur_subseq = -1; int cur_reg = SND_SOC_NOPM; struct snd_soc_dapm_context *cur_dapm = NULL; int ret, i; int *sort; if (power_up) sort = dapm_up_seq; else sort = dapm_down_seq; list_for_each_entry_safe(w, n, list, power_list) { ret = 0; /* Do we need to apply any queued changes? */ if (sort[w->id] != cur_sort || w->reg != cur_reg || w->dapm != cur_dapm || w->subseq != cur_subseq) { if (!list_empty(&pending)) dapm_seq_run_coalesced(card, &pending); if (cur_dapm && cur_dapm->seq_notifier) { for (i = 0; i < ARRAY_SIZE(dapm_up_seq); i++) if (sort[i] == cur_sort) cur_dapm->seq_notifier(cur_dapm, i, cur_subseq); } if (cur_dapm && w->dapm != cur_dapm) soc_dapm_async_complete(cur_dapm); INIT_LIST_HEAD(&pending); cur_sort = -1; cur_subseq = INT_MIN; cur_reg = SND_SOC_NOPM; cur_dapm = NULL; } switch (w->id) { case snd_soc_dapm_pre: if (!w->event) list_for_each_entry_safe_continue(w, n, list, power_list); if (event == SND_SOC_DAPM_STREAM_START) ret = w->event(w, NULL, SND_SOC_DAPM_PRE_PMU); else if (event == SND_SOC_DAPM_STREAM_STOP) ret = w->event(w, NULL, SND_SOC_DAPM_PRE_PMD); break; case snd_soc_dapm_post: if (!w->event) list_for_each_entry_safe_continue(w, n, list, power_list); if (event == SND_SOC_DAPM_STREAM_START) ret = w->event(w, NULL, SND_SOC_DAPM_POST_PMU); else if (event == SND_SOC_DAPM_STREAM_STOP) ret = w->event(w, NULL, SND_SOC_DAPM_POST_PMD); break; default: /* Queue it up for application */ cur_sort = sort[w->id]; cur_subseq = w->subseq; cur_reg = w->reg; cur_dapm = w->dapm; list_move(&w->power_list, &pending); break; } if (ret < 0) dev_err(w->dapm->dev, "ASoC: Failed to apply widget power: %d\n", ret); } if (!list_empty(&pending)) dapm_seq_run_coalesced(card, &pending); if (cur_dapm && cur_dapm->seq_notifier) { for (i = 0; i < ARRAY_SIZE(dapm_up_seq); i++) if (sort[i] == cur_sort) cur_dapm->seq_notifier(cur_dapm, i, cur_subseq); } list_for_each_entry(d, &card->dapm_list, list) { soc_dapm_async_complete(d); } }
dapm kcontrol的put回调
上面我们已经讨论了如何判断一个widget是否需要上电，以及widget的上电过程，一个widget的状态改变如何传递到整个音频路径上的所有widget。这些过程总是需要一个起始点：是谁触动了dapm，使得它需要执行上述的扫描和上电过程？事实上，以下几种情况可以触发dapm发起一次扫描操作：
1)声卡初始化阶段，snd_soc_dapm_new_widgets函数创建widget包含的kcontrol后，会触发一次扫描操作。
2)用户空间的应用程序修改了widget中包含的dapm kcontrol的配置值时，会触发一次扫描操作。
3)pcm的打开或关闭，会通过音频流widget触发一次扫描操作(在soc_pcm_prepare/close函数中，会调用snd_soc_dapm_stream_event()发出SND_SOC_DAPM_STREAM_START/START事件)。
4)驱动程序在改变了某个widget并把它加入到dapm_dirty链表后，主动调用snd_soc_dapm_sync函数触发扫描操作。
这里我们主要讨论一下第二种，用户空间对kcontrol的修改，最终都会调用到kcontrol的put回调函数。对于常用的dapm kcontrol，系统已经为我们定义好了它们的put回调函数：
snd_soc_dapm_put_volsw mixer类型的dapm kcontrol使用的put回调
snd_soc_dapm_put_enum_double mux类型的dapm kcontrol使用的put回调
snd_soc_dapm_put_enum_virt 虚拟mux类型的dapm kcontrol使用的put回调
snd_soc_dapm_put_value_enum_double 控制值不连续的mux类型的dapm kcontrol使用的put回调
snd_soc_dapm_put_pin_switch 引脚类dapm kcontrol使用的put回调
我们以mixer类型的dapm kcontrol的put回调讲解一下触发的过程：
/** * snd_soc_dapm_put_volsw - dapm mixer set callback * @kcontrol: mixer control * @ucontrol: control element information * * Callback to set the value of a dapm mixer control. * * Returns 0 for success. */ int snd_soc_dapm_put_volsw(struct snd_kcontrol *kcontrol, struct snd_ctl_elem_value *ucontrol) { struct snd_soc_dapm_context *dapm = snd_soc_dapm_kcontrol_dapm(kcontrol); struct snd_soc_card *card = dapm->card; struct soc_mixer_control *mc = (struct soc_mixer_control *)kcontrol->private_value; int reg = mc->reg; unsigned int shift = mc->shift; int max = mc->max; unsigned int mask = (1 << fls(max)) - 1; unsigned int invert = mc->invert; unsigned int val; int connect, change, reg_change = 0; struct snd_soc_dapm_update update; int ret = 0; if (snd_soc_volsw_is_stereo(mc)) dev_warn(dapm->dev, "ASoC: Control '%s' is stereo, which is not supported\n", kcontrol->id.name); val = (ucontrol->value.integer.value[0] & mask); connect = !!val; if (invert) val = max - val; mutex_lock_nested(&card->dapm_mutex, SND_SOC_DAPM_CLASS_RUNTIME); change = dapm_kcontrol_set_value(kcontrol, val); if (reg != SND_SOC_NOPM) { mask = mask << shift; val = val << shift; reg_change = soc_dapm_test_bits(dapm, reg, mask, val); } if (change || reg_change) { if (reg_change) { update.kcontrol = kcontrol; update.reg = reg; update.mask = mask; update.val = val; card->update = &update; } change |= reg_change; ret = soc_dapm_mixer_update_power(card, kcontrol, connect); card->update = NULL; } mutex_unlock(&card->dapm_mutex); if (ret > 0) soc_dpcm_runtime_update(card); return change; }
其中的dapm_kcontrol_set_value函数用于把设置值缓存到kcontrol对应的影子widget，影子widget是为了实现autodisable特性而创建的一个虚拟widget，影子widget的输出连接到kcontrol的source widget，影子widget的寄存器被设置为和kcontrol一样的寄存器地址，这样当source widget被关闭时，会触发影子widget被关闭，其作用就是kcontrol也被自动关闭从而在物理上断开与source widget的连接，但是此时逻辑连接依然有效，dapm依然认为它们是连接在一起的。 触发dapm进行电源状态扫描关键的函数是soc_dapm_mixer_update_power：
/* test and update the power status of a mixer or switch widget */ static int soc_dapm_mixer_update_power(struct snd_soc_card *card, struct snd_kcontrol *kcontrol, int connect) { struct snd_soc_dapm_path *path; int found = 0; lockdep_assert_held(&card->dapm_mutex); /* find dapm widget path assoc with kcontrol */ dapm_kcontrol_for_each_path(path, kcontrol) { found = 1; soc_dapm_connect_path(path, connect, "mixer update"); } if (found) dapm_power_widgets(card, SND_SOC_DAPM_STREAM_NOP); return found; }
最终，还是通过dapm_power_widgets函数，触发整个音频路径的扫描过程，这个函数执行后，因为kcontrol的状态改变，被断开连接的音频路径上的所有widget被按顺序下电，而重新连上的音频路径上的所有widget被顺序地上电，所以，尽管我们只改变了mixer kcontrol中的一个输入端的连接状态，所有相关的widget的电源状态都会被重新设定，这一切，都是自动完成的，对用户空间的应用程序完全透明，实现了dapm的原本设计目标。
