在接下来的几个小节中，会讲解几个音频的项目，现在想讲解第一个项目：对 耳麦拔插事件的处理，一起分为四个小节左右：
5.1 驱动程序上报耳麦拔插事件
5.2 在状态栏显示耳麦图标
5.3 耳麦拔插事件调用流程分析
5.4 切换声音通道流程
在讲解驱动程序之前，先讲解几个概念：
下面是编写输入系统的流程：
编写驱动程序如下（其使用两种方法实现）：
#include<linux/module.h>#include<linux/types.h>#include<linux/init.h>#include<linux/device.h>#include<linux/fs.h>#include<linux/err.h>#include<linux/switch.h>#include<linux/input.h>staticstructinput_dev*g_virtual_input;staticssize_tinput_test_store(structdevice*dev,structdevice_attribute*attr,constchar*buf,size_t count){long code;long val;char*endp;/* 如果字符串前面含有非数字, simple_strtol不能处理 */while((*buf ==' ')||(*buf =='\t'))
buf++;
code =simple_strtol(buf,&endp,0);/* 如果字符串前面含有非数字, simple_strtol不能处理 */while((*endp ==' ')||(*endp =='\t'))
endp++;
val =simple_strtol(endp,NULL,0);printk("emulate to report EV_SW: 0x%lx 0x%lx\n", code, val);input_event(g_virtual_input, EV_SW, code, val);input_sync(g_virtual_input);return count;}staticDEVICE_ATTR(test_input, S_IRUGO | S_IWUSR,NULL, input_test_store);staticintregister_input_device_for_jack(void){int err;/* 分配input_dev */
g_virtual_input =input_allocate_device();/* 设置 *//* 2.1 能产生哪类事件 */set_bit(EV_SYN, g_virtual_input->evbit);set_bit(EV_SW, g_virtual_input->evbit);/* 2.2 能产生这类事件中的哪些 *//* headset = 听筒 + MIC = SW_HEADPHONE_INSERT + SW_MICROPHONE_INSERT
* 同时上报 SW_HEADPHONE_INSERT 和 SW_MICROPHONE_INSERT, 就表示headset
* 为了简化, 对于android系统只上报SW_MICROPHONE_INSERT也表示headset
*/set_bit(SW_HEADPHONE_INSERT, g_virtual_input->swbit);set_bit(SW_MICROPHONE_INSERT, g_virtual_input->swbit);set_bit(SW_LINEOUT_INSERT, g_virtual_input->swbit);/* 2.3 这些事件的范围 */
g_virtual_input->name ="alsa_switch";/* 不重要 *//* 注册 */
err =input_register_device(g_virtual_input);if(err){input_free_device(g_virtual_input);printk("input_register_device for virtual jack err!\n");return err;}/* 创建/sys/class/input/inputX/test_input文件
* 可以执行类似下面的命令来模拟耳麦的动作:
* 触发上报headset插入: echo 4 1 > /sys/class/input/inputX/test_input
* 触发上报headset取下: echo 4 0 > /sys/class/input/inputX/test_input
*/
err =device_create_file(&g_virtual_input->dev,&dev_attr_test_input);if(err){printk("device_create_file for test_input err!\n");input_unregister_device(g_virtual_input);input_free_device(g_virtual_input);return err;}return0;}staticvoidunregister_input_device_for_jack(void){device_remove_file(&g_virtual_input->dev,&dev_attr_test_input);input_unregister_device(g_virtual_input);input_free_device(g_virtual_input);}/**************************************************************************************************************/staticstructswitch_dev g_virtual_switch;staticssize_tstate_test_store(structdevice*dev,structdevice_attribute*attr,constchar*buf,size_t count){long val;
val =simple_strtol(buf,NULL,0);printk("emulate to report swtich state: 0x%lx\n", val);switch_set_state(&g_virtual_switch, val);return count;}staticDEVICE_ATTR(test_state, S_IRUGO | S_IWUSR,NULL, state_test_store);staticintregister_switch_device_for_jack(void){int err;
g_virtual_switch.name ="h2w";
err =switch_dev_register(&g_virtual_switch);if(err){printk("switch_dev_register h2w err!\n");return err;}/* 创建/sys/class/switch/h2w/test_state文件
* 可以执行类似下面的命令来模拟耳麦的动作:
* 触发上报headset插入: echo 1 > /sys/class/switch/h2w/test_state
* 触发上报headset取下: echo 0 > /sys/class/switch/h2w/test_state
*/
err =device_create_file(g_virtual_switch.dev,&dev_attr_test_state);if(err){printk("device_create_file test err!\n");switch_dev_unregister(&g_virtual_switch);return err;}return0;}staticvoidunregister_switch_device_for_jack(void){device_remove_file(g_virtual_switch.dev,&dev_attr_test_state);switch_dev_unregister(&g_virtual_switch);}/**************************************************************************************************************/staticint __init virtual_jack_init(void){int err;
err =register_input_device_for_jack();
err =register_switch_device_for_jack();return0;}staticvoid __exit virtual_jack_exit(void){unregister_input_device_for_jack();unregister_switch_device_for_jack();}module_init(virtual_jack_init);module_exit(virtual_jack_exit);MODULE_AUTHOR("weidongshan@qq.com");MODULE_DESCRIPTION("Virutal jack driver for sound card");MODULE_LICENSE("GPL");
/* 创建/sys/class/switch/h2w/test_state文件
* 可以执行类似下面的命令来模拟耳麦的动作:
* 触发上报headset插入: echo 1 > /sys/class/switch/h2w/test_state
* 触发上报headset取下: echo 0 > /sys/class/switch/h2w/test_state
*/
/* 创建/sys/class/input/inputX/test_input文件
* 可以执行类似下面的命令来模拟耳麦的动作:
* 触发上报headset插入: echo 4 1 > /sys/class/input/inputX/test_input
* 触发上报headset取下: echo 4 0 > /sys/class/input/inputX/test_input
*/
下面说一下编写switch dev驱动的流程：
staticstructswitch_dev g_virtual_switch;/*戴米安耳机的拔插*/
g_virtual_switch.name ="h2w";
err =switch_dev_register(&g_virtual_switch);/*硬件触发，状态设置，中断上报*/switch_set_state(&g_virtual_switch, val);
下面是switch_set_state与输入子系统能够上报事件的一些对比：
voidswitch_set_state(structswitch_dev*sdev,int state)kobject_uevent(&sdev->dev->kobj, KOBJ_CHANGE);returnkobject_uevent_env(kobj, action,NULL);/*通过网络发送数据*/
retval =netlink_broadcast_filtered(uevent_sock, skb,0,1, GFP_KERNEL,kobj_bcast_filter,kobj);/*sbin/hotplug APP*/
retval =call_usermodehelper_exec(info, UMH_NO_WAIT);如何把程序编写到内就不讲解了，下小节我们开始做实验。
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