I am doing embedded system development with my EVM board. And now, i want to release my whole software to others. To get some referrences on how to package my software, i downloaded some other vendors' linux SDK.
The thing confused me is if its vendor modified the linux kernel, instead of releasing the SDK with a dirty kernel directly they all have a original clean kernel along with a patch containing this modification.
So,that is why? To avoid license? Linux kernel license requires the kernel not be spreaded with personal modification?
Thanks

Once you say 'embedded' abbreviations are poor form, because people like me don't know what ads you're been reading, and what you bought.

If the other manufacturer has applied a patch, you can diff it with the appropriate Linus version and you have his patch. It looks to me like you're doing some project based on hacked versions you get from competitors, instead of doing your own work. How many bugs and backdoors has your competitor put in there? How can you fix them? You don't know.
You don't know.

If you're only slightly serious and doing a home project - fine. Otherwise use genuine versions and don't take a lazy way out. Do work you can stand over.