本篇博客主要分析如何将audio_paths添加到内核中
首先看一下，audio_paths的定义：
static const struct snd_soc_dapm_route audio_paths[] = {
{ "Left Boost Mixer", "LINPUT1 Switch", "LINPUT1" },
{ "Left Boost Mixer", "LINPUT2 Switch", "LINPUT2" },
{ "Left Boost Mixer", "LINPUT3 Switch", "LINPUT3" },
{ "Left Input Mixer", "Boost Switch", "Left Boost Mixer", },
{ "Left Input Mixer", NULL, "LINPUT1", }, /* Really Boost Switch */
{ "Left Input Mixer", NULL, "LINPUT2" },
{ "Left Input Mixer", NULL, "LINPUT3" },
.....
};
在代码中，使用函数snd_soc_dapm_add_routes将route添加到内核中，如下所示：
snd_soc_dapm_add_routes(dapm, audio_paths, ARRAY_SIZE(audio_paths));
/**
* 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, ret;
for (i = 0; i < num; i++) {
ret = snd_soc_dapm_add_route(dapm, route);
.....
route++;
}
return 0;
}
EXPORT_SYMBOL_GPL(snd_soc_dapm_add_routes);
这个函数的关键就是snd_soc_dapm_add_route，在分析该函数之前，我们首先看一下route的种类：
1）常规route
{"sink" NULL "source"}
表示由route构造出来的path->connect = 1
2）sink widget是Mixer
{"Mixer", name1, "source1"}
{"Mixer", name2, "source2"}
即：
source1----->name1------>Mixer
source2----->name2------>Mixer
name1和name2代表两个snd_kcontrol_new，这两个kcontrol在Mixer widget中，该wiget含有：
a.Mixer本身的信息
b.2个snd_kcontrol_new: name1和name2
可以通过操作某个kcontrol来打开某条path
3）sink widget是Mux
{"Mux" value1, "source1"}
{"Mux" value2, "source2"}
source1 ---------value1
\
\
\-----------Mux
source2 --------- value2
Mux widget含有：
a.Mux本身信息
b.1个snd_kcontrol_new，它有两种取值：value和value2
这三种route是如何转换成path的呢？
猜测：
1）首先要找出source widget和sink widget，至于kcontrol，这个地方不会去找。为什么？
上篇博客中已经介绍，widget中kcontrol的创建是在machine驱动中，而这个地方只是codec驱动，还没有创建kcontrol，因此它在这个地方是不会去找的。
2）构造path
path->source = wsource; path->sink = wsink;
3）设置
path->connect的值：
a.如果kcontrol = NULL，则它是一条static path，此时path->connect=1.
b.如果kcontrol !=NULL，则它是一条dynamic path，它的path->connect是如何设置呢？
这个地方是根据widget sink的类型决定的，
b.1 sink widget为ADC、DAC等的path，该path一般来说都是直连的（无开关）
snd_soc_dapm_adc snd_soc_dapm_dac snd_soc_dapm_pga snd_soc_dapm_out_drv snd_soc_dapm_input snd_soc_dapm_output snd_soc_dapm_siggen snd_soc_dapm_micbias snd_soc_dapm_vmid snd_soc_dapm_pre snd_soc_dapm_post snd_soc_dapm_supply snd_soc_dapm_regulator_supply snd_soc_dapm_aif_in snd_soc_dapm_aif_out snd_soc_dapm_dai //将path放入dapm->card->paths链表中 list_add(&path->list, &dapm->card->paths); //将path的sink放入到widget的sources链表中。如何理解： //在widget中，source就是source，sink就是sink。而在audio_routes，即形成的path中，格式是sink---->source. //因此path中的sink刚好对应的是widget中的source list_add(&path->list_sink, &wsink->sources); list_add(&path->list_source, &wsource->sinks); path->connect = 1;
b.2 对于sink widget是Mixer的path，path->connect 需要根据寄存器的值进行确定
case snd_soc_dapm_switch:
case snd_soc_dapm_mixer:
case snd_soc_dapm_mixer_named_ctl:
ret = dapm_connect_mixer(dapm, wsource, wsink, path, control);
dapm_set_path_status
b.3 对于sink widget是Mux的path，path->connect需要根据寄存器的值进行确定
case snd_soc_dapm_mux:
case snd_soc_dapm_virt_mux:
case snd_soc_dapm_value_mux:
ret = dapm_connect_mux(dapm, wsource, wsink, path, control,&wsink->kcontrol_news[0]);
dapm_set_path_status//读寄存器，通过读出来的值再去判断该path是否连通
b.4 对于sink widget可以动态拔插的headphone、mic、line、speaker，它默认将path->connect设置为0。以后再根据实际情况，将path->connect设置为1.
比如说，插上耳机，对应的path设置为1
case snd_soc_dapm_hp:
case snd_soc_dapm_mic:
case snd_soc_dapm_line:
case snd_soc_dapm_spk:
list_add(&path->list, &dapm->card->paths);
list_add(&path->list_sink, &wsink->sources);
list_add(&path->list_source, &wsource->sinks);
path->connect = 0;
snd_soc_dapm_add_routes会导致path的创建，以及链表关系的形成，path->connect值的设置。但是注意一点：
Mux和Mixer中snd_kcontrol此时还没有被创建，snd_kcontrol的创建是在函数snd_soc_dapm_new_widgets中。
附：snd_soc_dapm_add_route源码
static int snd_soc_dapm_add_route(struct snd_soc_dapm_context *dapm,
const struct snd_soc_dapm_route *route)
{
struct snd_soc_dapm_path *path;
struct snd_soc_dapm_widget *wsource = NULL, *wsink = NULL, *w;
struct snd_soc_dapm_widget *wtsource = NULL, *wtsink = NULL;
const char *sink;
const char *control = route->control;
const char *source;
char prefixed_sink[80];
char prefixed_source[80];
int ret = 0;
if (dapm->codec && dapm->codec->name_prefix) {
snprintf(prefixed_sink, sizeof(prefixed_sink), "%s %s",
dapm->codec->name_prefix, route->sink);
sink = prefixed_sink;
snprintf(prefixed_source, sizeof(prefixed_source), "%s %s",
dapm->codec->name_prefix, route->source);
source = prefixed_source;
} else {
sink = route->sink;
source = route->source;
}
/*
* 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;
continue;
}
if (!wsource && !(strcmp(w->name, source))) {
wtsource = w;
if (w->dapm == dapm)
wsource = w;
}
}
/* use widget from another DAPM context if not found from this */
if (!wsink)
wsink = wtsink;
if (!wsource)
wsource = wtsource;
if (wsource == NULL || wsink == NULL)
return -ENODEV;
path = kzalloc(sizeof(struct snd_soc_dapm_path), GFP_KERNEL);
if (!path)
return -ENOMEM;
path->source = wsource;
path->sink = wsink;
path->connected = route->connected;
INIT_LIST_HEAD(&path->list);
INIT_LIST_HEAD(&path->list_source);
INIT_LIST_HEAD(&path->list_sink);
/* check for external widgets */
if (wsink->id == snd_soc_dapm_input) {
if (wsource->id == snd_soc_dapm_micbias ||
wsource->id == snd_soc_dapm_mic ||
wsource->id == snd_soc_dapm_line ||
wsource->id == snd_soc_dapm_output)
wsink->ext = 1;
}
if (wsource->id == snd_soc_dapm_output) {
if (wsink->id == snd_soc_dapm_spk ||
wsink->id == snd_soc_dapm_hp ||
wsink->id == snd_soc_dapm_line ||
wsink->id == snd_soc_dapm_input)
wsource->ext = 1;
}
/* connect static paths */
if (control == NULL) {
list_add(&path->list, &dapm->card->paths);
list_add(&path->list_sink, &wsink->sources);
list_add(&path->list_source, &wsource->sinks);
path->connect = 1;
return 0;
}
/* connect dynamic paths */
switch (wsink->id) {
case snd_soc_dapm_adc:
case snd_soc_dapm_dac:
case snd_soc_dapm_pga:
case snd_soc_dapm_out_drv:
case snd_soc_dapm_input:
case snd_soc_dapm_output:
case snd_soc_dapm_siggen:
case snd_soc_dapm_micbias:
case snd_soc_dapm_vmid:
case snd_soc_dapm_pre:
case snd_soc_dapm_post:
case snd_soc_dapm_supply:
case snd_soc_dapm_regulator_supply:
case snd_soc_dapm_aif_in:
case snd_soc_dapm_aif_out:
case snd_soc_dapm_dai:
list_add(&path->list, &dapm->card->paths);
list_add(&path->list_sink, &wsink->sources);
list_add(&path->list_source, &wsource->sinks);
path->connect = 1;
return 0;
case snd_soc_dapm_mux:
case snd_soc_dapm_virt_mux:
case snd_soc_dapm_value_mux:
ret = dapm_connect_mux(dapm, wsource, wsink, path, control,
&wsink->kcontrol_news[0]);
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, wsource, wsink, path, control);
if (ret != 0)
goto err;
break;
case snd_soc_dapm_hp:
case snd_soc_dapm_mic:
case snd_soc_dapm_line:
case snd_soc_dapm_spk:
list_add(&path->list, &dapm->card->paths);
list_add(&path->list_sink, &wsink->sources);
list_add(&path->list_source, &wsource->sinks);
path->connect = 0;
return 0;
}
return 0;
err:
dev_warn(dapm->dev, "asoc: no dapm match for %s --> %s --> %s\n",
source, control, sink);
kfree(path);
return ret;
}
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