Hello CMata_Intel and thanks for the answer.
Yes, I have looked through this file and saw the guide on how to build the full image.
I was trying to ask of there was a way to rebuild the kernel only, without building the whole image.
And if I consider building the whole image I have another question:
I want to experiment with the kernel, applying an RT_PREEMPT patch. The BSP guide tells where to find the defconfig file, but not where the kernel sources are. Before starting the build I would want to apply the patch on the kernel sources. How can I do this?
Check out this thread for the advice on rebuilding the kernel during development cycle: https://communities.intel.com/thread/57206?sr=inbox
As far as the patching is concerned, Yocto patches the kernel during the build process. The Yocto document referenced in the thread above has some hints about patching the kernel.
Generally, the best way woul be to add your patches to SRC_URL variable in the kernel's recipe and Yocto will apply them properly for you.
If you aren't sure the patch will apply at all, run "bitbake -c devshell linux-yocto", that will configure all the environment variables, apply the default patches, unpack sources and drop you into the shell with the kernel source directory as CWD. Then you can work on applying the patch manually and checking it out, eventually tweaking it to apply. Then add it to the SRC_URL and let Yocto build the kernel for you.
There are quite a few smaller things you may face along the way, feel free to post further questions here.
So can some one tell me how to compile kernel only for the Yocto 2.1 release. I read this and got an older kernel working but I want to work with the new kernel because the SPI drivers are properly defined in this.