[yocto] Preempt-rt kernel build for beagleboard

[Yu Pan]

Hi Bruce,

Thanks for commenting :-)

You shouldn't have needed to do this part, since the board already has
> a preempt-rt BSP description:
>
> http://git.yoctoproject.org/**cgit/cgit.cgi/linux-yocto-3.4/**
> tree/meta/cfg/kernel-cache/**bsp/beagleboard/beagleboard-**
> preempt-rt.scc?h=meta<http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-3.4/tree/meta/cfg/kernel-cache/bsp/beagleboard/beagleboard-preempt-rt.scc?h=meta>
>
> And when you build the linux-yocto-rt kernel with that board, that
> description should be found, and it enables all the base options already.
>
> If you look in your build, what does the file 'linux/meta/top_tgt'
> contain ?
>

This was what puzzles me as well. I thought bitbake should pickup what is
specified in beagleboard-preempt-rt.scc to produce the .config in the
kernel build directory. But it did not, at least for the PREEMPT part.
Below is the PREEMPT related configs in the .config without manually doing
the menuconfig:

# CONFIG_PREEMPT_RCU is not set
CONFIG_PREEMPT_NONE=y
# CONFIG_PREEMPT_VOLUNTARY is not set
# CONFIG_PREEMPT__LL is not set
# CONFIG_PREEMPT_RTB is not set
# CONFIG_PREEMPT_RT_FULL is not set

Follow your pointer, I checked linux/meta/top_tgt, it indeed points to
meta/cfg/kernel-cache/bsp/beagleboard/beagleboard-preempt-rt.scc, which
includes ktypes/preempt-rt (why not ktypes/preempt-rt.scc?). In
ktypes/preempt-rt.cfg (included by ktypes/preempt-rt.scc),
CONFIG_PREEMPT_RT_FULL=y is there. So why not this configuration fragment
not picked up in the final .config?

Cheers
Pan Yu
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