Alsa或TinyAlsa添加控制接口

背景

Platform： RK3399
Kernel： v4.4.10

项目需要添加一个控制外部电路Mute的接口，主要是控制一个GPIO

过程

DTS配置

添加GPIO配置
类似：

amp-gpios = <&gpio1 17 GPIO_ACTIVE_HIGH>;
...
&pinctrl {
	...
	xxx_gpios: xxx-gpios {
		rockchip,pins = <3 16 RK_FUNC_GPIO &pcfg_pull_none>, 
				<1 17 RK_FUNC_GPIO &pcfg_pull_none>;
	}
	...
}

驱动源码添加

在驱动probe函数中获取gpio相关信息：
xxx->amp_gpio = of_get_named_gpio(np, "amp-gpios", 0);

if (gpio_is_valid(xxx->amp_gpio)) {
	ret = devm_gpio_request_one(&i2c->dev, xxx->amp_gpio,GPIOF_OUT_INIT_LOW, "xxx amp ctl");
	if (ret != 0)
		return ret;
}

在snd_kcontrol_new中添加dapm kcontrol:
```
SOC_SINGLE_BOOL_EXT("Local AMP Hw Mute", 1, local_amp_hw_mute_get, local_amp_hw_mute_put),
```
相关dapm kcontrol定义可查看文件：kernel/include/sound/soc.h

添加对应的xhandler_get和xhandler_put函数，来控制对应的GPIO

static int local_amp_hw_mute_get(struct snd_kcontrol *kcontrol,
				struct snd_ctl_elem_value *ucontrol)
{
	struct snd_soc_codec *codec = snd_soc_kcontrol_codec(kcontrol);
	struct xxx_priv *xxx = snd_soc_codec_get_drvdata(codec);

	ucontrol->value.integer.value[0] = xxx->amp_mute_en;

	return 0;
}

static int local_amp_hw_mute_put(struct snd_kcontrol *kcontrol,
				struct snd_ctl_elem_value *ucontrol)
{
	struct snd_soc_codec *codec = snd_soc_kcontrol_codec(kcontrol);
	struct xxx_priv *xxx = snd_soc_codec_get_drvdata(codec);
	
	unsigned int val = ucontrol->value.integer.value[0];

	if (val > 1)
		return -EINVAL;

	mutex_lock(&xxx->lock);

	xxx->amp_mute_en = val;
	if (gpio_is_valid(xxx->amp_gpio)) {
		gpio_set_value(xxx->amp_gpio, 1-val);
	}

	mutex_unlock(&xxx->lock);

	return 0;
}