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Wandboard Kernel Development
Working on the Wandboard Linux kernel
2014-03-02 07:30:00 -0800
wandboard
wandboard
linux
kernel development

I am working on a Wandboard Quad board using tools from the Yocto Project.

I have already built a system for this board, but now I want to make some kernel modifications.

I don't want to use bitbake during development because that's a pretty slow process.

But I will be using the cross-compiler and other tools that Yocto has already built and when I'm done with development I will create a patch for use with Yocto.

The Linux kernel that is running now is built from rules in the Freescale meta-fsl-arm-extra layer. I am using the [dora] branch of both the Yocto and Freescale meta-layers.

The default kernel version is 3.0.35.

This can be found out by first looking at the meta-fsl-arm-extra/conf/machine/wandboard-quad.conf configuration file and noting this line

PREFERRED_PROVIDER_virtual/kernel ?= "linux-wandboard"

Then looking under meta-fsl-arm-extra/recipes-kernel/linux where there are some recipe files

  • linux-wandboard_3.0.35.bb
  • linux-wandboard.inc

And this directory

  • linux-wandboard-3.0.35/

Inside linux-wandboard.inc you can find the URL for the Linux source.

...
SRC_URI = "git://github.com/wandboard-org/linux.git \
           file://defconfig \
"
...

So the first thing is to clone this repository.

scott@hex:~$ git clone git://github.com/wandboard-org/linux.git linux-wandboard

This will take a little while.

The recipe file linux-wandboard_3.0.35.bb has the commit that we want to use

...
# Wandboard branch - based on 4.0.0 from Freescale git
SRCREV = "d35902c77a077a25e4dfedc6aac11ba49c52c586"
LOCALVERSION = "-4.0.0-wandboard"
...

I'm going to call my new branch [work] just to keep things simple.

scott@hex:~/linux-wandboard$ git checkout -b work d35902c
Switched to a new branch 'work'

A quick check that I'm on the correct commit

 scott@hex:~/linux-wandboard$ git log --oneline | head -5
 d35902c defconfig: Small updates to easy demos
 98cef90 prism.c: add BTN_TOUCH events to prism singletouch device
 ce086c4 Wandboard : Add comments reflecting EDM pin numbers of GPIOs
 672d8f3 Add support for Future Electronics FWBADAPT-7WVGA expansion board
 821af75 Wandboard : Add support for edm framwork

To get the kernel source to the same state as what is currently running, I need to apply some additional patches that were included in the linux-wandboard_3.0.35.bb recipe.

...
# GPU support patches
SRC_URI += "file://drm-vivante-Add-00-sufix-in-returned-bus-Id.patch \
file://0001-ENGR00255688-4.6.9p11.1-gpu-GPU-Kernel-driver-integr.patch \
file://0002-ENGR00265465-gpu-Add-global-value-for-minimum-3D-clo.patch \
file://0003-ENGR00261814-4-gpu-use-new-PU-power-on-off-interface.patch \
file://0004-ENGR00264288-1-GPU-Integrate-4.6.9p12-release-kernel.patch \
file://0005-ENGR00264275-GPU-Correct-suspend-resume-calling-afte.patch \
file://0006-ENGR00265130-gpu-Correct-section-mismatch-in-gpu-ker.patch"
...

Here's one way to go about it

scott@hex:~/linux-wandboard$ git am ~/poky-dora/meta-fsl-arm-extra/recipes-kernel/linux/linux-wandboard-3.0.35/*.patch

Applying: ENGR00255688 4.6.9p11.1 [gpu]GPU Kernel driver integration
Applying: ENGR00265465 gpu:Add global value for minimum 3D clock export
Applying: ENGR00261814-4 gpu: use new PU power on/off interface
/oe25/linux-wandboard/.git/rebase-apply/patch:15: trailing whitespace.
#if LINUX_VERSION_CODE < KERNEL_VERSION(3,5,0)
/oe25/linux-wandboard/.git/rebase-apply/patch:17: space before tab in indent.
                regulator_enable(Os->device->gpu_regulator);
/oe25/linux-wandboard/.git/rebase-apply/patch:30: trailing whitespace.
#if LINUX_VERSION_CODE < KERNEL_VERSION(3,5,0)
/oe25/linux-wandboard/.git/rebase-apply/patch:35: space before tab in indent.
                imx_gpc_power_up_pu(false);
warning: 4 lines add whitespace errors.
Applying: ENGR00264288-1 [GPU]Integrate 4.6.9p12 release kernel part code
/oe25/linux-wandboard/.git/rebase-apply/patch:1973: space before tab in indent.
        newSemaphore = (struct semaphore *)kmalloc(gcmSIZEOF(struct semaphore), GFP_KERNEL | gcdNOWARN);
warning: 1 line adds whitespace errors.
Applying: ENGR00264275 [GPU]Correct suspend/resume calling after adding runtime pm.
Applying: ENGR00265130 gpu:Correct section mismatch in gpu kernel driver
Applying: drm/vivante: Add ":00" sufix in returned bus Id

A check of the latest commits after the patches

scott@hex:/oe25/linux-wandboard$ git log --oneline | head -15
60f7201 drm/vivante: Add ":00" sufix in returned bus Id
3ee67f3 ENGR00265130 gpu:Correct section mismatch in gpu kernel driver
32e78d7 ENGR00264275 [GPU]Correct suspend/resume calling after adding runtime pm.
5f8fe6f ENGR00264288-1 [GPU]Integrate 4.6.9p12 release kernel part code
8081dc7 ENGR00261814-4 gpu: use new PU power on/off interface
9e9c852 ENGR00265465 gpu:Add global value for minimum 3D clock export
b30614f ENGR00255688 4.6.9p11.1 [gpu]GPU Kernel driver integration
d35902c defconfig: Small updates to easy demos
98cef90 prism.c: add BTN_TOUCH events to prism singletouch device
ce086c4 Wandboard : Add comments reflecting EDM pin numbers of GPIOs
672d8f3 Add support for Future Electronics FWBADAPT-7WVGA expansion board
821af75 Wandboard : Add support for edm framwork
a66d9e6 Add support for Prism I2C touchscreen
5074e84 Add basic EDM framework
929768a wandboard: modify mipi-csi to ipu mux setting

In this case, the patches were not applied in the same order as the Yocto build would have done it.

The drm-vivante-Add-00... patch got applied last instead of first because of the alpha-numeric ordering. This could potentially be a problem. You'll know it if the patch command fails.

In this case it was okay.

Some alternatives to apply the list of patches in the correct order would be

  1. Apply the patches one at a time manually
  2. Use quilt after first creating a series file with the correct ordering

It's easy to experiment.

You can always reset the repository to the starting commit this way

scott@hex:~/linux-wandboard$ git reset --hard d35902c
HEAD is now at d35902c defconfig: Small updates to easy demos

Create an environment script like the following to point to the Yocto built cross-compiler tools. TMPDIR comes from the setting in your build/conf/local.conf

--- wandboard-yocto-env.sh ---
MACHINE=wandboard-quad
TMPDIR=/oe21/tmp-poky-dora-build

SYSROOTSDIR=${OETMP}/sysroots
STAGEDIR=${SYSROOTSDIR}/`uname -m`-linux/usr

export KERNELDIR=${SYSROOTSDIR}/${MACHINE}/usr/src/kernel

PATH=${STAGEDIR}/bin:${STAGEDIR}/bin/cortexa9hf-vfp-neon-poky-linux-gnueabi:${PATH}

unset CFLAGS CPPFLAGS CXXFLAGS LDFLAGS

export ARCH="arm"
export CROSS_COMPILE="arm-poky-linux-gnueabi-"

The default Wandboard kernel config in the meta-fsl-arm-extra repository is not convenient for direct use. (Not every option is supplied so you'll have to wade through questions when running 'make oldconfig'). I find it easiest to just grab the final .config from the Yocto build directory. This will also ensure you pick up any kernel 'configuration fragments'.

Using the same TMPDIR, copy the .config file to the source directory

scott@hex:~/linux-wandboard$ cp <TMPDIR>/work/wandboard_quad-poky-linux-gnueabi/linux-wandboard/3.0.35-r0/git/.config .config

After that, the following commands will build the uImage kernel and modules.

make oldconfig (or make menuconfig)
make include/linux/version.h
make uImage
make modules

You can add a -jN argument to make to speed things up.

For example

make -j4 uImage
make -j4 modules