I am a newbie with kernel matters so I apologize in advance for what
newbie type setup question. My feeling is that if I send this query to the
more general Arm Fedora forum, the mere mention of kernel will provoke
glazed eyes :-)
Unlikely, I do it all the time, happy to help ;-)
The background is that I have an OEM board based on a TI AM3352 OMAP
SoC looking somewhat like a Beaglebone black. Recently I've been exploring
getting this running under Fedora. In order to get it working I've cobbled
together the F22 minimal image along with a device tree blob created by a
colleague for this board, and a customised MLO/u-boot.
My next task is to look through and understand the arm kernel sources,
customize various aspects of the kernel config for my board and re-build.
It seems that instructions are here:
However, I want to cross compile on a host system. To ease this process I
have set up a Fedora x86 box, also running f22, which is going to be the
host build machine.
I decided I should build from source rpm and was following the wiki
instructions(rpmdev-setuptree etc.) up to the point here...
The easiest way to do this is:
Install the Fedora packaging tools:
"dnf install fedora-packager"
Clone the kernel package source and switch the F-22 branch:
"fedpkg clone -a kernel"
"fedpkg switch-branch f22"
The kernel config for the am33xx devices like the BBB is in a file
called config-armv7. It's a bit confusing to get started but basically
there's inheritance on the config files config-generic ->
config-arm-generic -> config-armv7-generic -> config-armv7
Most of the bits related to the am33xx are in a section titled "# AM33xx/43xx"
Adjust the config as you like. Once you've done that run "fedpkg prep"
which will make sure all your config changes aren't missing anything.
Then do "fedpkg srpm" to create a .src.rpm
Then to cross compile run the following command:
rpmbuild --rebuild --target armv7hl --with=cross --without=perf
--without=tools --without=debuginfo --without=pae --define="_arch arm"
--define="_build_arch arm" --define="__strip
That will builder you the kernel and modules. You want to leave out
tools/perf as they don't tend to cross compile well but it's unlikely
they'll differ much from the ones we already ship, I've never had an
issue with those.
At this point I'd like to actually have a target of arm7l for my
entering this gets me an unknown target error (possibly not surprising
given the build machine/target architecture difference!).
Use the command above and you should be good.
My build machine does have a suitable linaro Arm compiler in place.
occurs to me that I need a different kernel spec and to indicate to my
build system to use my compiler. Hopefully this can be achieved via some
slightly modified step from that given in the wiki page? Or should I be
tackling this in a completely different way?
The above command will prompt you to install the Fedora cross compiler
toolchain, I would recommend using that, it works fine for am33xx and
other ARMv7 devices, YMMV with Linaro toolchain.