When one issues a command
git-clone git://git.freedesktop.org/git/mesa/drm

, one will download and create a directory called linux-core under drm.
linux-core serves to provide the source code for generating
kernel modules of the graphic cards or graphic chipsets.

A big QUESTION: It seems it is most likely that the content of linux-core
will not matches the content of the existing /usr/src/kernels/kernel-version/Makefile, or the existing kernel source.
This will potentially make generation of kernel modules (ko) extremely
difficult. Am I right to say that ? Why would the freedesktop people want
to do such a thing if this is the case ? Isn't linux hard enough already ?

Appreciate anyone who will share his/her opinion on this.

The "freedesktop people" aren't trying to do such a thing. If you didn't install your current kernel from source there should be a source package available for it through your package manager. Using git will download the latest version of the source code, so you'd need to create a working kernel from it if you wish to use it for kernel modules.

sorry I sort of understand arguments but not quite.

The end of http://wiki.x.org/wiki/Development/git
has a script that is attempting to compile drm from the source.

The particular relevant line are (init() is to download drm from git repos):


init()
{
for repo in $REPOS; do
echo "Cloning $repo";
git clone $repo;
done
cd macros
echo "Building macros"
./autogen.sh --prefix="$PREFIX";
($MAKE);
make install
cd ..
}



# build drm
cd drm
./autogen.sh --prefix="$PREFIX"
($MAKE)
make -C linux-core
# assuming you're on Linux, otherwise use bsd-core
make install
cd ..


Either there is some logic flow or I am still missing something.

Total_MADMAN, you said it is possible to get the correct linux-core
from the package manager ? But my FC9 tells me something different.


[ckgan@fc9 ~]$9 ~]$ rpm -qva | grep kernel
kernel-headers-2.6.25-14.fc9.x86_64
kerneloops-0.10-11.fc9.x86_64
kernel-2.6.25-14.fc9.x86_64
kernel-2.6.25.11-97.fc9.x86_64
kernel-devel-2.6.25-14.fc9.x86_64
[ckgan@fc9 ~]$ ls -l /usr/src/kernels/2.6.25-14.fc9.x86_64/drivers/char/drm
total 8
-rw-r--r-- 1 root root 3806 2008-05-01 18:19 Kconfig
-rw-r--r-- 1 root root 2345 2008-05-01 18:19 Makefile
[ckgan@fc9 ~]$