Enabling adb support with Linux kernel for new platform

If you are developing/porting a new Linux kernel for some android platform, the first thing we need is a debug support. When we are porting very basic kernel, we might have UART for debugging purpose, but those have dependencies over limited UART cables and since we normally have more USB cables as those are required to charging mobiles, its always better to have some kind of debugging over USB cable. Android allows us to connect to device shell using its own Android Debug Bridge (ADB) protocol.

Android Debug Bridge (adb) is a versatile command-line tool that lets you communicate with a device. The adb command facilitates a variety of device actions, such as installing and debugging apps, and it provides access to a Unix shell that you can use to run a variety of commands on a device. Reference Android Studio

The first step we need to do is to make sure, we have USB ADB gadget support enabled in Linux kernel.

Before KERNEL version 3.10, the Android had a separate ADB driver at drivers/usb/gadget/f_adb.c and can be enable from menuconfig. After 3.10, Android has deprecated f_adb.c and has replaced with Accessory driver at drivers/usb/gadget/function/f_accessory.c

For compiling kernel, Follow steps from “Compile custom Linux kernel for Android / AOSP on Ubuntu”

Flash and connect USB cable to Host

dmesg looks like..

[11621.761441] usb 2-1: new high speed USB device using ehci_hcd and address 27
[11621.912445] usb 2-1: configuration #1 chosen from 1 choice
[11621.959123] Initializing USB Mass Storage driver…
[11621.959341] scsi6 : SCSI emulation for USB Mass Storage devices
[11621.959551] usbcore: registered new interface driver usb-storage
[11621.959555] USB Mass Storage support registered.
[11621.964209] usb-storage: device found at 27
[11621.964212] usb-storage: waiting for device to settle before scanning
[11626.961587] usb-storage: device scan complete
[11626.962259] scsi 6:0:0:0: Direct-Access     <NULL>   <NULL>           0000 PQ: 0 ANSI: 2
[11626.963870] sd 6:0:0:0: Attached scsi generic sg1 type 0
[11626.966200] sd 6:0:0:0: [sdb] Attached SCSI removable disk

 $ lsusb 
Bus 002 Device 027: ID 18d1:0002

$ lsusb -v -d 18d1:0002 

Bus 002 Device 027: ID 18d1:0002

Device Descriptor:
bLength                18
bDescriptorType         1
bcdUSB               2.00
bDeviceClass            0 (Defined at Interface level)
bDeviceSubClass         0
bDeviceProtocol         0
bMaxPacketSize0        64
idVendor           0x18d1
idProduct          0x0002
bcdDevice            2.16
iManufacturer           1
iProduct                2
iSerial                 3
bNumConfigurations      1

Configuration Descriptor:
bLength                 9
bDescriptorType         2
wTotalLength           55
bNumInterfaces          2
bConfigurationValue     1
iConfiguration          0
bmAttributes         0xe0 ( Self Powered, Remote Wakeup)
MaxPower                2mA

Interface Descriptor:
bLength                 9
bDescriptorType         4
bInterfaceNumber        0
bAlternateSetting       0
bNumEndpoints           2
bInterfaceClass         8 Mass Storage
bInterfaceSubClass      6 SCSI
bInterfaceProtocol     80 Bulk (Zip)
iInterface              0

Endpoint Descriptor:
bLength                 7
bDescriptorType         5
bEndpointAddress     0x81  EP 1 IN
bmAttributes            2
Transfer Type            Bulk
Synch Type               None
Usage Type               Data
wMaxPacketSize     0x0200  1x 512 bytes
bInterval               0

Endpoint Descriptor:
bLength                 7
bDescriptorType         5
bEndpointAddress     0x01  EP 1 OUT
bmAttributes            2
Transfer Type            Bulk
Synch Type               None
Usage Type               Data
wMaxPacketSize     0x0200  1x 512 bytes
bInterval               1

Interface Descriptor:
bLength                 9
bDescriptorType         4
bInterfaceNumber        1
bAlternateSetting       0
bNumEndpoints           2
bInterfaceClass       255 Vendor Specific Class
bInterfaceSubClass     66
bInterfaceProtocol      1
iInterface              0

Endpoint Descriptor:
bLength                 7
bDescriptorType         5
bEndpointAddress     0x82  EP 2 IN
bmAttributes            2
Transfer Type            Bulk
Synch Type               None
Usage Type               Data
wMaxPacketSize     0x0200  1x 512 bytes
bInterval               0

Endpoint Descriptor:
bLength                 7
bDescriptorType         5
bEndpointAddress     0x02  EP 2 OUT
bmAttributes            2
Transfer Type            Bulk
Synch Type               None
Usage Type               Data
wMaxPacketSize     0x0200  1x 512 bytes
bInterval               0

3) add a udev rule of your Host with following information

$ vim /etc/udev/rules.d/51-android.rules 

SUBSYSTEM==”usb”, SYSFS{idVendor}==”18d1″, MODE=”0666″

4) Change the permissions

$ chmod 777 /etc/udev/rules.d/51-android.rules

5) Now disconnect and reconnect USB cable and run “adb devices”

 $ adb kill-server 

(may be need to kill adb server if was already running)

 $ adb devices 

List of devices attached
0123456789ABCDEF    device

 $ adb shell 

On device
=========

# ls -l /dev/android*
crw-rw—- adb      adb       10,  60 2010-07-01 07:20 android_adb
crw-rw—- adb      adb       10,  61 2010-07-01 07:20 android_adb_enable

adbd process running

# root      883   1     3364   156   ffffffff 0000f444 S /sbin/adbd

** Modifications for conencting with adb if using another USB Vendor ID.
==============================================================
1) Modify system/core/adb/usb_vendors.c as following.
+++ b/adb/usb_vendors.c
@@ -69,6 +69,7 @@
#define VENDOR_ID_PANTECH       0x10A9
// Qualcomm’s USB Vendor ID
#define VENDOR_ID_QUALCOMM      0x05c6
+#define VENDOR_ID_CORPORATION      0xabcd

/** built-in vendor list */
@@ -90,6 +91,7 @@ int builtInVendorIds[] = {
VENDOR_ID_KYOCERA,
VENDOR_ID_PANTECH,
VENDOR_ID_QUALCOMM,
+    VENDOR_ID_CORPORATION,
};

2) change udev rule(/etc/udev/rules.d/51-android.rules) as following,
SUBSYSTEM==”usb”, SYSFS{idVendor}==”abcd”, MODE=”0666″

then recompile android, and used recompiled “out/host/linux-x86/bin/adb” binary for getting adb shell.

# ./out/host/linux-x86/bin/adb devices

List of devices attached
0123456789ABCDEF    offline

Here, “0123456789ABCDEF” is the sring from usb descriptor “Serial Number” String descriptor as a part of “usb device descriptor”