i.MX Yocto Project: How can I patch the kernel?

[#1]

The Linux Kernel is just another recipe for Yocto, so learning to patch it you learn to patch any other package. In the other hand, Yocto **should not** be used for package development, but in those rare cases follow the below steps. It is assumed that you have already build the package you want to patch.

1. Create the patch or patches. In this example we are patching the Linux kernel for [wandboard-dual](http://www.wandboard.org/) machine; in other words, the value of MACHINE on the `build/conf/local.conf` is `MACHINE ??= 'wandboard-dual'`. In case you already have the patches, make sure these can be nicely applied with the commands `git apply --check <PATCH_NAME>`, and jump this step

build $ cd tmp/work/wandboard_dual-poky-linux-gnueabi/linux-wandboard/3.0.35-r0/git

build $ # Edit any files you want to change

build $ git add <modified file 1> <modified file 2> .. # Select the files you want to commit

build $ git commit -s -m '<your commit's title>' # Create the commit

build $ git format-patch -1 # Create the patch

2. Create a new layer (see document i.MX Yocto Proyect: How can I create a new Layer?)

3. On the new layer (e.g `meta-fsl-custom`) , create the corresponding subfolders and the `.bbfile`

sources $ mkdir -p meta-fsl-custom/recipes-kernel/linux/linux-wandboard-3.0.35/

sources $ cat > meta-fsl-custom/recipes-kernel/linux/linux-wandboard_3.0.35.bbappend

FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}-${PV}:"

SRC_URI += "file://0001-calibrate-Add-printk-example.patch"

PRINC := "${@int(PRINC) + 1}" # SEE NOTE BELLOW

^d

(The PRINC variable is not needed starting at Yocto 1.6 ([RFC] base.bbclass: Deprecate the PRINC logic - Patchwork))

4. Move the patch to the new layer

sources $ cp \

../build/tmp/work/wandboard_dual-poky-linux-gnueabi/linux-wandboard/3.0.35-r0/git/0001-calibrate-Add-printk-example.patch \

meta-fsl-custom/recipes-kernel/linux/linux-wandboard-3.0.35

5. Setup the enviroment and clean previous package's build data (sstate)

fsl-community-bsp $ . setup-environment build

build $ bitbake -c cleansstate linux-wandboard

6. Compile and Deploy

build $ bitbake -f -c compile linux-wandboard

build $ bitbake -c deploy linux-wandboard

7. Insert the SD into your Host and copy the `uImage` into the first partition. Do not forget to unmount the partition before removing the card!

build $ sudo cp tmp/deploy/images/uImage /media/Boot\ wandbo/

8. Insert the SD into your board and test your change.

[florianl]

And how can I add completely new drivers to the kernel? Of course, I can add it at first to the SRC_URI - but where should they be located and how do I tell the kernel to load it for compiling?

[LeonardoSandova]

Yocto is not for developing purposes. Add the driver as you would do it normally: create the drivers files, .c and .h, an place it under the drivers folder, the do the changes on Kconfig files. Then test it (built-in and as a module) with make and dd. When it is ready, the best way is to point the SRC_URI to your git repo (github? or you can install gitolite or something similar on your host, if you do not want the world to see your code as this point) then bake it with Yocto. You can still use patches, but I have not seen a whole driver as a patch....

Leo

[LeonardoSandova]

PaulEggleton Thanks for you comment on PRINC variable. I added a note regarding the deprecation of it.

[matt0308]

Do you have a sample to change kernel configuration in customer layer? chrishossack and I encountered the same problem that defconfig/.cfg file in customer layer doesn't update automatically. You can also find the discussion list as "Changing the Kernel configuration for i.MX6 SABRE​​ . Please advise once you can help us to solve the problem. Thank you.

Matt

[chenwen]

Hi Leo,

Do we need to add something to the conf/bblayers.conf to tell bitbake the new layer?

I have done the steps above. But it seems that the patch doesn't contained in the tasks.