I am newbie on Linux kernel and just started using Beagle bone black development board. So this might be a silly question.

I downloaded the beaglebone linux kernel from https://github.com/beagleboard/linux and able to build and boot up the beagle bone board.

My questions are:

1. what is the difference(just top level view not in depth) between the mainline Linux kernel and beaglebone black linux kernel.
2. Why there is a separate repository maintained for beaglebone board linux kernel.

For the above two questions my assumed answers are(I might be completely wrong).

1. We need Beaglebone board specific drivers and configurations to support linux running in beaglebone. So to mainline linux kernel beaglebone board specific drivers are added.

2. If a new development board(hardware) is made,then we need to customise(make board specific changes and add drivers) the mainline linux kernel to support the new board.

Are my assumptions correct?
Please help.

From wikipedia I got this.
“Mainline Linux has only solid support for a small subset of the many devices that run Linux. Non-mainline support is provided by independent projects, such as Yocto or Linaro, but in many cases the kernel from the device vendor is needed.[147] Using a vendor kernel likely requires a board support package.”