[yocto] Building Out-of-Tree Modules on the BBB Target

Tue May 14 10:30:37 PDT 2019

Hello Chris, Bruce,

I have some additional data to share with you both, since I have tried
something. And here is my take on the things!

> 1. Build using a bb recipe.
> Take a look at meta-skeleton/recipes-kernel/hello-mod for an example.
> You just need to add meta-skeleton to your bblayers.conf and then
>  bitbake hello-mod

I looked into this example, and, yes, it is classic kernel module
definition out of the tree. With some outdated data, all cool, the
YOCTO designer should take care himself to fix these data, if using
this stuff.

But this is NOT mandatory, since I can add out of the tree module NOT
actually using built-in module. I just use .../tmp/deploy/images/bbb/*
generated stuff, since I have automated scripts which are bringing all
these on my BBB target. Then I tftp my source code module to the
target.

> 2. Build from the SDK:
> First, add the kernel source to the SDK by adding this to conf/local.conf
>  TOOLCHAIN_TARGET_TASK_append = " kernel-devsrc"

YES, this is THE command which should generate
/usr/src/kernel(s)/`uname -r` or similar... But adding it to
local.conf and after deleting kernel, then regenerating bitbake -k
core-image-minimal does not bring this path into the rootfs image!?

I did it actually using meta-bbb, and using poky referent distro as
two additional layers to the more complex bbb image!
https://github.com/jumpnow/meta-bbb.git

The (KAS - you can figure out out of it local.conf) script I am using
to build such a BBB image is here:
https://github.com/ZoranStojsavljevic/bbb-yocto/blob/master/bbb-releases/bbb-warrior/kas-bbb-warrior.yml

I did not try it with BBB reference poky only! Maybe I should try it
as only referent poky? What do you think?

Does in this case is SDK build really mandatory??? Should NOT be!

> Once the SDK is installed, generate the kernel headers:
>  sudo -i
>  . /opt/poky/2.6.2/environment-setup-cortexa8hf-neon-poky-linux-gnueabi
>  cd /opt/poky/2.6.2/sysroots/cortexa8hf-neon-poky-linux-gnueabi
>  cd /usr/src/kernel
>  make oldconfig scripts
>  exit

This is in nutshell the same what I did (a bit different) for Embedded
Debian. This is already on the target BBB, NOT while building YOCTO
BBB image!

> Finally, build your module using a Makefile like this
>  obj-m := hello-mod.o
>  all:
>        make -C $(SDKTARGETSYSROOT)/usr/src/kernel M=$(shell pwd)

As said before: bringing my own module into the target BBB (I have my
own examples, and I build them on the target with the almost the same
Makefiles)

Zoran
_______

On Sun, May 12, 2019 at 3:15 PM Chris Simmonds <chris at 2net.co.uk> wrote:
>
> Hi Zoran,
>
> There are two ways to do this
>
> 1. Build using a bb recipe.
> Take a look at meta-skeleton/recipes-kernel/hello-mod for an example.
> You just need to add meta-skeleton to your bblaysers.conf and then
>   bitbake hello-mod
>
>
> 2. Build from the SDK:
> First, add the kernel source to the SDK by adding this to conf/local/conf
>   TOOLCHAIN_TARGET_TASK_append = " kernel-devsrc"
>
> Then build the SDK
>   bitbake -c populate_sdk [your image recipe]
>
> Once the SDK is installed, generate the kernel headers:
>   sudo -i
>   . /opt/poky/2.6.2/environment-setup-cortexa8hf-neon-poky-linux-gnueabi
>   cd /opt/poky/2.6.2/sysroots/cortexa8hf-neon-poky-linux-gnueabi
>   cd /usr/src/kernel
>   make oldconfig scripts
>   exit
>
> Finally, build your module using a Makefile like this
>
>   obj-m := hello-mod.o
>   all:
>         make -C $(SDKTARGETSYSROOT)/usr/src/kernel M=$(shell pwd)
>
>
> HTH,
> Chris
>
> On 12/05/2019 11:53, Zoran Stojsavljevic wrote:
> > Hello to the YOCTO community,
> >
> > I am using (to build the target for Beagle Bone Black) the following script:
> > https://github.com/ZoranStojsavljevic/bbb-yocto
> > https://github.com/ZoranStojsavljevic/bbb-yocto/blob/master/bbb-yocto.sh
> >
> > The latest kernel I am using from the following repo:
> > https://github.com/jumpnow/meta-bbb
> >
> > Is kernel 5.0.14 .
> >
> > Here is the snippet of the boot traces:
> > Starting kernel ...
> >
> > [    0.000000] Booting Linux on physical CPU 0x0
> > [    0.000000] Linux version 5.0.14-jumpnow (oe-user at oe-host) (gcc
> > version 8.3.0 (GCC)) #1 Fri May 10 13:12:33 UTC 2019
> > [    0.000000] CPU: ARMv7 Processor [413fc082] revision 2 (ARMv7), cr=10c5387d
> > [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing
> > instruction cache
> > [    0.000000] OF: fdt: Machine model: TI AM335x BeagleBone Black
> > [    0.000000] Memory policy: Data cache writeback
> > [    0.000000] cma: Reserved 16 MiB at 0x9f000000
> > [    0.000000] CPU: All CPU(s) started in SVC mode.
> > [    0.000000] AM335X ES2.1 (sgx neon)
> > [    0.000000] random: get_random_bytes called from
> > start_kernel+0xa4/0x460 with crng_init=0
> > [    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 130048
> > [    0.000000] Kernel command line: console=ttyO0,115200n8
> > root=/dev/ram0 ip=dhcp
> >
> > According to the documentation, the following:
> > 2.10.1. Building Out-of-Tree Modules on the Target
> > https://www.yoctoproject.org/docs/latest/kernel-dev/kernel-dev.html
> >
> > I tried to find /usr/src/kernels/5.0.14... Directory, since I see
> > from the build that kernel-dev and kernel-devsrc are included:
> > [user at fedora29-ssd bbb-yocto]$ bitbake -s | grep kernel
> > core-image-kernel-dev                                 :1.0-r0
> > kernel-devsrc                                         :1.0-r0
> > kernel-selftest                                       :1.0-r0
> >
> > THE PROBLEM: But I could not find ob BBB target /usr/src/kernels
> > directory at all!?
> >
> > Two questions here?
> > [1] Do you have any advice on this problem (what I am missing here)?
> > [2] Alternative to [1]: how I can use cross compiler from
> > .../build/tmp to build Out-of-Tree Module for the BBB target on the
> > host?
> >
> > Thank you,
> > Zoran
> > _______
> >
>
>
> --
> Chris Simmonds, trainer and consultant at 2net
> http://www.2net.co.uk
> Author of "Mastering Embedded Linux Programming"