Guidance regarding Android Kernel Porting from one device to other

I own a Samsung Galaxy 3 and want to port kernels available for other Android Devices. I have all building environment ready. I have C knowledge also. What exactly I dont understand is how and what all things porting involves, which codes should be modified in what way?

If someone could help me. It would be great.

Thanks in advance.

Ok I got it. But the real problem is I dont understand one thing.

What needs to be changed in the source code so that to make it compatible in other device? Can someone explain me that?

Upvotes: 3

Answers (3)

Devarsh Thakkar

Reputation: 131

I am also into android porting stuff for quite some time I suggest the following route :

Read

You need to have basic knowledge of android porting and AOSP source code, directory stucture hierarchy. I suggest you to start reading https://books.google.co.in/books/about/Embedded_Android.html?id=plHsngEACAAJ&hl=en and also refer https://source.android.com/devices/index.html as good guys pointed out you can also google android porting related groups and become a member there, if you are stuck on a issue there are chances similar issue might have been faced by someone else previously.

Observe

AOSP code : Parallely you need to dive in to the android source e.g from links like https://android.googlesource.com/ observe which components are placed where in the source code, what are the updates from previous android release (like ART replaced dalvik in LL), at top level there would be generic code, code specific to your hardware called HAL in hardware/ and device/ folder.

Kernel code : In the kernel also you need to observe the directory structure and know which things lie where like SoC specific code will be in arch/ directory defconfigs (used for selecting kernel configuration) will be arch//configs/ directory. Also there are good books available for linux kernel, you can google them and start reading them also.

While porting kernel you need to take care of following

1.If in the new kernel there is already support of SoC which is used in hardware to be ported then you need to add only device specific changes like suppose you want to port new kernel version to samsung galaxy s3, you can take a reference android kernel having exynos support and then you need to make changes only for adding support for samsung galaxy s3.

For that you need to have reference of some old kernel having support of s3, from there you can study patches which have been added to add support for s3 and port those patches to newer kernel.

Experiment

First you can only port the bare minimum changes required to up the platform, compile and flash it on your platform, then observe the output, if everything looks fine than go on for next changes otherwise try to solve the issue.

Thanks, Devarsh

Upvotes: 1

Sylvain Huard

Reputation: 1398

Idolon gives a good suggestion. In theory what is written there is true. In practice, it's a little more involving. I've been porting Android Kernel for months now. My goal was to have a custom S5PV210 processor module on my custom board with my custom I/O. I have the source code for Samsung's galaxy tab and several Samsung's android smartphone as well as a few versions (Froyo, Gingerbread) for the Samsung's Evaluation board (SMDKV210 for S5PV210 CPU). FYI, S5PC110 is a close derivative. Here is what I found out. Eventhough all the device drivers are supposed to be built in a very modular way and independent from each other and you should be able to replace them with similar devices, the way Samsung did it is not exactly that. To give you one example is about power management. In many low level drivers dealing with hardware devices, it calls some specific routine for other hardware devices like power management chip. So, When you change the choice of drivers in the "make xconfig" or "make menuconfig" it will remove the source code of what you don't want and add the one you want but, there are still other modules that are calling the low level function you removed. When building, you will get tons of unresolved external because you removed a power management chip that your hardware doesn't have but is used in the source you started with. I looked through several Samsung's device source code and they have branched very early on. They have been adapted by different teams and it would be a major amount of work to go from one device to the other from one source kit.

Here is how I succeeded: I bought an S5PV210 evaluation board with an already ported Android Kernel (Gingerbread). All the power management and inter dependant issues where already cleaned-up. Then, form a working kit, I could change the device I needed (the one you can't buy without a 100K unit/yr commitment) without getting stuck with the interdependancy. Then I could even change LCD resolution (from 800x480 to 1024x768), touchscreen, Cell modem etc etc. The whole thing takes about a month worth of work with only one guy (me).

Starting with a Galaxytab or other commercial device made me waste months of headakes with no useful results but the thing I've learned.

There is one requirement to succeed on my approach. You have to know the hardware you are working on. As an example, you need to know what touch screen your hardware has (chipset) to select the driver and were is it connected to hook it up to the right device (USB, Serial etc). That the same thing for all other devices (power managemnt chip, keypad, backlight, LCD etc etc)

Hope that is useful to give you an idea of the work involved and how you can do it.

Upvotes: 4

Volo

Reputation: 29438

You should take a look at the cached copy of Android Platform Developer's Guide and at android-porting google group.

There is also an old but useful article about porting Android to Nokia N810, which will give you some hints about Android Linux kernel porting.