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Android KitKat 4.4平台开发-添加USB ADB和MTP功能支持

ADB和MTP是Android基于USB实现的两个重要功能,极大地方便了用户在PCAndroid设备之间的互操作,比如传输文件、安装应用、开发调试应用。

 

本文讲述如何在特定软硬件平台下支持Android ADB和MTP功能。

Android版本: KitKat 4.4.2

Linux内核版本: 3.10 (Vendor Kernel)

硬件平台: Atmel SAMA5D3 SoC


针对Linux内核的更改

Merge Android Linux内核USB Gadget驱动到处理器厂商Linux内核

Vendor Linux内核和Android Linux内核都是基于Mainline Linux内核进行开发的。芯片厂商和Google公司都会修改Linux内核代码以支持自己的硬件平台及Android系统。新添加的功能和支持在稳定后会重新合并到后续版本的Mainline Linux内核。

 

从内核版本3.3开始,Android Linux内核开始与Mainline Linux内核融合,但目前(本文使用的内核版本3.10)还是有一部分功能没有并入Mainline Linux内核,比如用于支持Android ADB, Mass Storage和MTP/PTP等功能的Android USB Gadget驱动。

如果要在某个芯片厂商的硬件平台上运行Android系统,并支持这些USB相关的功能,必须将Android Linux内核中的Android USB Gadget驱动并入Vendor Linux内核。有些处理器芯片厂商会提供支持Android的Linux 内核,如果要命名的话,可以称之为Vendor Android Linux内核,而如果我们所使用的硬件平台,厂商没有提供完整支持Android的Linux内核,Android平台开发者可以自己合并代码以添加支持。

 

可以在多个源找到Android Linux内核的源代码,本文使用github上的源:

https://github.com/android/kernel_common  branch:android-3.10


从Android Linux内核获得Android USB Gadget驱动的补丁

受影响的文件

drivers/usb/gadget/Kconfig

drivers/usb/gadget/Makefile

drivers/usb/gadget/android.c

drivers/usb/gadget/composite.c

drivers/usb/gadget/f_accessory.c

drivers/usb/gadget/f_audio_source.c

drivers/usb/gadget/f_fs.c

drivers/usb/gadget/f_mtp.c

drivers/usb/gadget/f_rndis.c

drivers/usb/gadget/rndis.c

drivers/usb/gadget/u_serial.c

drivers/usb/gadget/udc-core.c

include/linux/usb/f_accessory.h

include/linux/usb/f_mtp.h

include/uapi/linux/usb/f_accessory.h

include/uapi/linux/usb/f_mtp.h


使用gitformat-patch命令生成所需要的补丁(下面的命令并不是普遍适用的,只是一个参考,需要根据具体情况灵活变通)

git format-patch -n29 drivers/usb/gadget/  include/linux/usb/f_mtp.h  include/linux/usb/f_accessory.h include/uapi/linux/usb/f_mtp.h  include/uapi/linux/usb/f_accessory.h


 

得到如下补丁

0001-usb-gadget-Add-Android-Composite-Gadget-driver.patch

0002-usb-gadget-mtp-Add-MTP-PTP-function.patch

0003-usb-gadget-adb-Add-ADB-function.patch

0004-usb-gadget-accessory-Add-Android-Accessory-function.patch

0005-usb-gadget-adb-allow-freezing-in-adb_read.patch

0006-usb-gadget-adb-do-not-set-error-flag-when-dequeuing-.patch

0007-usb-gadget-adb-Only-enable-the-gadget-when-adbd-is-r.patch

0008-usb-gadget-composite-Fix-corruption-when-changing-co.patch

0009-usb-gadget-android-Fix-product-name.patch

0010-usb-gadget-android-Add-FunctionFS.patch

0011-usb-gadget-accessory-Fix-section-mismatch.patch

0012-usb-gadget-Fix-usb-string-id-allocation.patch

0013-USB-gadget-Add-ACCESSORY_SET_AUDIO_MODE-control-requ.patch

0014-USB-gadget-f_accessory-Add-support-for-HID-input-dev.patch

0015-USB-gadget-f_audio_source-New-gadget-driver-for-audi.patch

0016-usb-gadget-f_fs-Fix-enumeration-in-fullspeed-mode.patch

0017-usb-gadget-accessory-Fix-section-mismatch-again.patch

0018-usb-gadget-android-Fixes-and-hacks-to-make-android-u.patch

0019-HACK-usb-gadget-Fix-enumeration-on-boot.patch

0020-usb-gadget-Fix-android-gadget-driver-build.patch

0021-usb-gadget-android-Fixes-and-hacks-to-make-android-u.patch

0022-usb-gadget-android-move-init-to-late_initcall-for-no.patch

0023-usb-gadget-android-3.10-fixes.patch

0024-USB-remove-duplicate-out-endpoint-creation-in-MTP-mo.patch

0025-usb-gadget-android-Remove-device-if-probe-fails.patch

0026-usb-gadget-f_mtp-move-userspace-interface-to-uapi.patch

0027-usb-gadget-f_accessory-move-userspace-interface-to-u.patch

0028-fix-false-disconnect-due-to-a-signal-sent-to-the-rea.patch

0029-drivers-usb-gadget-64-bit-related-type-fixes.patch


应用补丁

将这些patches复制到Vendor Linux内核源代码根目录下,使用git am命令将这些patches应用到Vendor Linux内核

git am  *.patch

 

内核配置

为了让内核支持USB ADBMTP功能,在编译前还需要在内核配置中使能相应选项。

Kernel Configuration

    > Device Drivers

        > USB Support

            > USB Gadget Support

                > Android Composite Gadget





针对Android的更改

从内核版本3.8开始,adb功能的实现发生了变化,把它的实现从内核代码中移除,在用户空间借助usbfunctionfs功能实现adb

内核 commit history

commit de8cff675b3de92ad4bb18a69cfe19091e810f49

Author:Benoit Goby <benoit@android.com>

Date:Mon Nov 5 18:47:08 2012 -0800

   usb: gadget: Fix android gadget driver build

   Removed obsolete f_adb function

   Change-Id:Idfb4110429bc0ea63f493c68ad667f49ca471987

   Signed-off-by: Benoit Goby<benoit@android.com>

 

android commit history

system/core

commitfd96db17b7f07eb6615af01fd1908b74383bf04b

Author:Andrzej Pietrasiewicz <andrzej.p@samsung.com>

Date:Fri Jan 13 15:13:46 2012 +0100

   FunctionFS: initial implementation

   This is the second version of a patch whichdemonstrates the possibility

   of using adbd (Android Debug Bridge daemon)with a generic FunctionFS gadget

   instead of a custom adb usb gadget in theLinux kernel. It contains changes

   introduced after Benoit‘s review - thank youBenoit.

   The patch adds a new usb access layer toadbd using FunctionFS. The former

   usb access method is still available. Themethod is chosen at runtime

   depending if /dev/usb-ffs/adb/ep0 or/dev/android_adb is accessible.

   How to use on the target device:

   $ insmod g_ffs.ko idVendor=<vendor ID>iSerialNumber=<some string>

   $ mount -t functionfs adb /dev/usb-ffs/adb-o uid=2000,gid=2000

   $ ./adbd

   This patch requires a patch to bionic whichadds <linux/usb_functionfs.h>

   which is an exact copy of the relevant filein the linux kernel.

   Change-Id:I4b42eb267ffa50fca7a5fba46f388a2f083e8b2d

   Signed-off-by: Andrzej Pietrasiewicz<andrzej.p@samsung.com>

   Signed-off-by: Kyungmin Park<kyungmin.park@samsung.com>

   [benoit@android.com: detect at runtime iffunctionfs is mounted

   or fallback using f_adb]

   Signed-off-by: Benoit Goby<benoit@android.com> 


为了使能adb功能,还需要在usb启动配置脚本中挂载usb functionfs文件系统

当前目录:<Android源代码根目录>/device/atmel

补丁如下:

diff--git a/sama5d3/init.sama5-ek.usb.rc b/sama5d3/init.sama5-ek.usb.rc

index80a2efa..be101e8 100644

---a/sama5d3/init.sama5-ek.usb.rc

+++b/sama5d3/init.sama5-ek.usb.rc

@@-1,3 +1,9 @@

+onfs

+mkdir /dev/usb-ffs 0770 shell shell

+mkdir /dev/usb-ffs/adb 0770 shell shell

+mount functionfs adb /dev/usb-ffs/adb uid=2000,gid=2000

+write /sys/class/android_usb/android0/f_ffs/aliases adb

+

 on property:sys.usb.config=mtp,adb

   write /sys/class/android_usb/android0/enable0

   write/sys/class/android_usb/android0/idVendor 03EB