Building which kernel?

[John Whitmore]

I've a question regarding the building of the linux kernel, more specifically
which kernel to build. 

I've previously built the kernel for an 86 arch but this time I want to build
for the RaspberryPi. I can easily get the current version of the installed
kernel with the "uname -a"  command but that doesn't tell me the git repo
where the kernel originated. I'd imagine that it's from the RPi git repo, but
that adds another level of confusion as that git repo doesn't have any tags at
all. So even given the version number from uname how to check out a suitable
version of the kernel.

I could take the latest from the RPi repo and use "make oldconfig" but I
wonder how far, in kernel versions, I can jump and not affect the installed
libs and utilities which have been built against another version of the
kernel?

I've read various documentation on building the linux kernel but that's never
really mentioned, mainly I guess as you're building for the x86 Arch. But even
there can you jump major versions of kernel without effecting other installed
SW in the system?

John