本文主要是介绍Android之 MTP框架和流程分析 (3)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
前面转发了篇博客介绍了MTP, 偏重于上层，已经很清楚了。这篇侧重于底层,按照一定的流程讲。
1. 代码位置
packages/providers/MediaProvider/src/com/android/providers/media/MtpReceiver.java
packages/providers/MediaProvider/src/com/android/providers/media/MtpService.java
packages/providers/MediaProvider/src/com/android/providers/media/MediaProvider.java
frameworks/base/media/java/android/mtp/MtpServer.java
frameworks/base/media/java/android/mtp/MtpDatabase.java
frameworks/base/media/java/android/mtp/MtpStorage.java
frameworks/base/media/java/android/mtp/MtpPropertyGroup.java
frameworks/base/media/java/android/mtp/MtpPropertyList.java
frameworks/base/media/java/android/mtp/MtpConstants.java
frameworks/base/media/jni/android_mtp_MtpServer.cpp
frameworks/base/media/jni/android_mtp_MtpDatabase.cpp
frameworks/av/media/mtp/MtpServer.h
frameworks/av/media/mtp/MtpServer.cpp
frameworks/av/media/mtp/MtpDatabase.h
frameworks/base/services/java/com/android/server/usb/UsbDeviceManager.java (UsbManager, UsbService)
kernel/drivers/usb/* (主要是android.c, f_mtp.c)
2. 在Settings设置mtp后，代码执行
Usbanager.SetCurrentFunction()
->UsbService.SetCurrentFunction()
->UsbDeviceManager.setCurrentFunctions()
-> mHandler.sendMessage(MSG_SET_CURRENT_FUNCTIONS)
->setEnabledFunctions(functions, makeDefault);
->SystemProperties.set("persist.sys.usb.config", functions);
此时会调用到init.usb.rc执行相应的代码
如果直接开机，开机时会在设置persist.sys.usb.config/sys.usb.config时执行init.usb.rc中代码（没有经过framework及以上代码）。
write /sys/class/android_usb/android0/enable 0/1
以上代码对应执行enable_store (android.c)
enable_store
1)enabled
f->enable(f_holder->f);
adb_android_function_enable
android_disable
usb_ep_dequeue
usb_remove_config
android_enable(dev);
usb_add_config
usb_gadget_connect
2)disabled
android_disable(dev);
usb_ep_dequeue
usb_remove_config
f->disable(f_holder->f)
adb_android_function_disable
usb_add_config(android_bind_config) composite.c
bind()
android_bind_config()
android_bind_enabled_functions()
f->bind_config()
mtp_function_bind_config(mtp)
adb_function_bind_config(adb)
-> usb_add_function()
usb_remove_config()
reset_config(cdev);
unbind_config(cdev, config);
f->unbind(config, f);
****_function_unbind_config()
config->unbind(config);
write /sys/class/android_usb/android0/functions mtp
以上代码对应执行functions_store (android.c)
functions_store()
-> android_enable_function()
-> list_add_tail
3. 如果开机后，连上USB线，首先执行chargr检测，然后是枚举过程 （以高通某芯片为例），这小节讲充电器检测
kernel\drivers\power\qpnp-charger.c
rc = devm_request_irq(chip->dev, chip->usbin_valid.irq,
qpnp_chg_usb_usbin_valid_irq_handler,
IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
"usbin-valid", chip);
qpnp_chg_usb_usbin_valid_irq_handler()中断处理函数，检测USB插入拔出
在连USB开机的情况下，这个处理函数会在qpnp_charger_probe()调用。
首先是电源恢复工作，
power_supply_set_present()
->msm_otg_set_vbus_state(POWER_SUPPLY_PROP_PRESENT)
->msm_otg_sm_work()
->pm_runtime_resume()
->msm_otg_runtime_resume()
->msm_otg_resume()
此时会看到log "USB exited from low power mode"
开始充电器检测工作
主要函数式msm_chg_detect_work() in msm_otg.c
通常USB线的检测状态变化
USB_CHG_STATE_UNDEFINED->USB_CHG_STATE_WAIT_FOR_DCD（循环几次）->USB_CHG_STATE_DCD_DONE
USB线的检测结果是USB_SDP_CHARGER，
此时会设置otg->phy->state=b_peripheral, 并设置current=100mA
4. 枚举过程
4.1 中断
ci13xxx_msm.c
ret = request_irq(wake_irq, ci13xxx_msm_resume_irq,
IRQF_TRIGGER_RISING | IRQF_ONESHOT, "usb resume", NULL);
ret = request_irq(_udc_ctxt.irq, msm_udc_irq, IRQF_SHARED, pdev->name, pdev);
msm_udc_irq()直接调用udc_irq()，处理PM and tr complete
isr_reset_handler/isr_suspend_handler/isr_resume_handler/isr_tr_complete_handler
msm_otg.c
Vbus检测中断
ret = request_irq(motg->irq, msm_otg_irq, IRQF_SHARED,
"msm_otg", motg);
msm_otg_irq()->queue_work(system_nrt_wq, &motg->sm_work);->msm_otg_sm_work()
插OTG 线后中断
msm_pmic_id_irq(), ID pin
4.2 调用过程
ci13xxx_udc.c
isr_reset_handler/isr_suspend_handler/isr_resume_handler/isr_tr_complete_handler
（我还不太熟，略过这个部分）
4.3 判读HS, FS
ci13xxx_udc.c
udc_probe()
udc->gadget.speed = USB_SPEED_UNKNOWN;
udc->gadget.max_speed = USB_SPEED_HIGH; //最大速度
isr_resume_handler()
udc->gadget.speed = hw_port_is_high_speed() ? USB_SPEED_HIGH : USB_SPEED_FULL;
HS/FS是通过函数hw_port_is_high_speed()得到
4.4 判断Host/Device
msm_otg_start_peripheral(on=1)
这里通过判断是SDP_CHARGER,然后设成peripheral(device).
qpnp_chg_usb_usbin_valid_irq_handler: qpnp_chg_usb_usbin_valid_irq_handler usbin-valid triggered: 1 host_mode: 0
上面就可以打印出host_mode, 是通过下面函数得到
host_mode = qpnp_chg_is_otg_en_set(chip);
接OTG线后，可以通过如下中断处理函数看出
msm_pmic_id_irq(), 主要处理函数msm_pmic_id_status_w()
也可以通过函数得到msm_otg_read_pmic_id_state()
PMIC: ID clear host
PMIC: ID set device
5. 下面才是MTP的单独部分
5.1 start MTP server
android_work()发送uevent(USB_STATE=CONFIGURED)给上层
packages/providers/MediaProvider/src/com/android/providers/media/MtpReceiver.java
handleUsbState()
intent = new Intent(context, MtpService.class);
context.startService(intent);
packages/providers/MediaProvider/src/com/android/providers/media/MtpService.java
onStartCommand
manageServiceLocked() MtpService.java "starting MTP server in MTP mode"
mServer = new MtpServer(mDatabase, mPtpMode);
MtpServer(MtpDatabase database, boolean usePtp) frameworks/base/media/java/android/mtp/MtpServer.java
mServer.start();
frameworks/base/media/jni/android_mtp_MtpServer.cpp
native_setup
android_mtp_MtpServer_setup
int fd = open("/dev/mtp_usb", O_RDWR);
mtp_open() f_mtp.c
MtpServer* server = new MtpServer(fd, getMtpDatabase(env, javaDatabase),..)
packages/providers/MediaProvider/src/com/android/providers/media/MtpService.java
mServer.start();
run() frameworks/base/media/java/android/mtp/MtpServer.java
native_run frameworks/base/media/jni/android_mtp_MtpServer.cpp
android_mtp_MtpServer_run
server->run();
MtpServer::run() frameworks/av/media/mtp/MtpServer.cpp
5.2 主要处理函数
frameworks/av/media/mtp/MtpServer.cpp
MtpServer::run()
infinite loop; read request; send data/response (write)
Read part
mRequest.read(fd);
MtpRequestPacket::read() (MtpRequestPacket mRequest;)
::read(fd, mBuffer, mBufferSize);
mtp_read() f_mtp.c
Write data/response
mData.write
MtpDataPacket::write(int fd)
::write(fd, mBuffer, mPacketSize);
mtp_write() f_mtp.c
mResponse.write
MtpResponsePacket::write
::write(fd, mBuffer, mPacketSize);
mtp_write() f_mtp.c
Event
MtpServer::doGetObject()
ioctl(mFD, MTP_SEND_FILE_WITH_HEADER, (unsigned long)&mfr);
mtp_ioctl() in f_mtp.c
MtpServer::doSendObject()
ret = ioctl(mFD, MTP_RECEIVE_FILE, (unsigned long)&mfr);
mtp_ioctl() in f_mtp.c
MtpServer::sendObjectAdded/sendObjectRemoved/sendStoreAdded/sendStoreRemoved/sendDevicePropertyChanged
MtpServer::sendEvent(MtpEventCode code, uint32_t param1)
MtpEventPacket::write(int fd)
::ioctl(fd, MTP_SEND_EVENT, (unsigned long)&event);
mtp_ioctl() in f_mtp.c
mtp_send_event()
开始的几个操作
MTP_OPERATION_OPEN_SESSION (1002)
MTP_OPERATION_GET_DEVICE_INFO (1001)
MTP_OPERATION_GET_OBJECT_PROPS_SUPPORTED (9801)
MTP_OPERATION_GET_OBJECT_PROPS_SUPPORTED (9801)
MTP_OPERATION_GET_DEVICE_PROP_DESC (1014)
MTP_OPERATION_GET_OBJECT_PROP_LIST (9805)
6. Debug方法
首先看看是哪部分出问题了
a. 检查main log, UsbDeviceManager, setEnabledFunctions()是否正常
b. 检查property, persist.sys.usb.config, sys.usb.config, sys.usb.state
c. 检查sysfs, functions and state, vid, pid
d. 检查kernel log, 能否看到sent uevent(USB_STATE=CONFIGURED), 同时看看main log, UsbDeviceManager
e. 检查main log/kernel, MTP server启动是否正常
f. 如果正常看看命令接收和response是否正常
针对不同出错地方，仔细看相应部分代码
调试工具
USB sniffer 方便看到所有数据，从协议上看看出错地方，尤其是可能是PC问题时
对比方法
换PC, 换手机的方法来对比测试
7. 正常log
mtp_bind_config
msm_otg : USB exited from low power mode
msm_otg : chg_type = USB_SDP_CHARGER
msm_hsusb msm_hsusb: vbus online
msm_hsusb msm_hsusb: CI13XXX_CONTROLLER_RESET_EVENT received
msm_hsusb msm_hsusb: CI13XXX_CONTROLLER_CONNECT_EVENT received
msm_hsusb msm_hsusb: reset
msm_otg : Avail curr from USB = 100
android_work: android_work: did not send uevent (0 0 (null))
android_work: android_work: sent uevent USB_STATE=CONNECTED
msm_hsusb msm_hsusb: reset
android_work: android_work: sent uevent USB_STATE=DISCONNECTED
android_work: android_work: sent uevent USB_STATE=CONNECTED
msm_otg : Avail curr from USB = 500
android_work: android_work: sent uevent USB_STATE=CONFIGURED
MtpService: starting MTP server in MTP mode
mtp_open
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