[yocto] Problem building the linux kernel outside source directory for mips

[Michael Stickel]

Hi,

I am new to yocto, so I don't know if this is the right list.

I tried to build a kernel for the MTX-1 platform that uses an AU1500 
which is a MIPS32 based SoC.
After some work I got the standard kernel (3.8.4) used in poky 9 to work.
But I encountered some problems:

In poky-dylan-9.0.0/meta/recipes-kernel/linux/linux-yocto.inc the 
builddir is set to 
"${WORKDIR}/linux-${MACHINE}-${LINUX_KERNEL_TYPE}-build", but 
KERNEL_EXTRA_ARGS does not contain O="${B}". How is the the out of 
source build of the kernel meant to work?

The task do_kernel_configme trashed my kernel config. This may be 
because defconfig is copied to ${B}/.config and do_kernel_configme is 
executed in ${S} and does not find .config.

Is the intended behavior of the out of source build for the kernel 
documented.

BTW: The kernel works and boots the core-image-minimal with usb USB 
Storage as rootfs.

Best regards
Michael