Architectures/Fedora ARM Kernels
Building and Installing a Fedora Kernel Package on ARM Systems
To be able to build and install a Fedora kernel package on ARM systems in a similar manner to installing on an x86 PC.
Since ARM-based hardware varies greatly, I decided to start with a single architecture and focus on the board(s) for which I had access. It is my hope that this can be expanded to support other ARM variants and boards over time. The specific ARM systems initially targeted were the Beagle-xM and Panda boards. These are TI OMAP3 and OMAP4, respectively. Only armv7l builds were supported.
Support has now been added to the kernel sources for the CompuLab Trim Slice (NVIDIA Tegra 2), and it may be built for armv5tel, armv7l, and armv7hl. This is available in the Fedora kernel as of version kernel-220.127.116.11-0.fc15.
Although F13 Beta is the base version of Fedora currently running on the boards, a more recent stable kernel from F15 was selected for the kernel baseline. The plan is to track the F15 kernel versions, keeping up with the most recent builds until F16 is released.
This newer kernel version has a dependency on a newer (F15 based) version of linux-firmware, so it was also built and installed for F13.
Building the Kernel Package
The kernel.spec file and Makefile.config were modified to add ARM OMAP specific support, and an applicable kernel config file was added. The kernel package was then built on a Panda board using the following command:
rpmbuild -ba --target=armv7l SPECS/kernel.spec
The source and binary packages are available via yum:
Details on setting up and using the repository are covered below.
The Fedora ARM kernel source tree is also available in git:
git clone ssh://git.fedorahosted.org/git/arm.git git branch kernel origin/kernel
fedpkg --dist=f13 srpm arm-koji build dist-f13 --arch-override=armv7l --scratch kernel-<KERNEL_VERSION>.fc13.src.rpm
Installing the Fedora ARM Kernel
Both of the boards selected for testing use the U-Boot bootloader, so support was added to the grubby package to automate the creation of appropriate U-Boot images for the kernel being installed. Automatic boot of the installed kernel is accomplished through configuring the U-Boot autoboot script to use those U-Boot image files.
- U-Boot does not support a "boot menu", like lilo or grub
- U-Boot partitions are vfat, which means no hard links
- U-Boot does not support symlinks
- U-Boot will use an autoboot script (boot.scr)
- The kernel will boot using an initrd
- The U-Boot partition (vfat) will be mounted on
- the default boot images will use standard named files (i.e. uImage, uInitrd)
To automate the kernel installation for U-Boot, the grubby package was modified as follows:
- require uboot-tools
- add sections to handle U-Boot images in both update and remove
- run mkimage in the RPM posttrans script if U-Boot is configured
- copy the new images to uImage and uInitrd (making it the default)
- remove the corresponding version of U-Boot images when a kernel is removed
Multiple kernel version images may be installed, and kernel versions may be switched by simply copying the desired image versions to uImage and uInitrd and rebooting. The only negative is some wasted space in the U-Boot partition, since two copies of the default kernel and initrd are stored.
No U-Boot specific changes were made to the kernel package, so it can be installed elsewhere without using the modified grubby, although in that case the U-Boot files would not be automatically updated.
A simple text file was added that keeps a log of the installed kernel versions (assuming they were installed via yum or rpm). When a new kernel is installed its version is appended to the list. When a kernel is removed its version entry is removed from the list. The last entry in the list is always assumed to be the default. If the default kernel is removed, the "new default" version of the U-Boot image files (the new "last" version in the list) are copied to uImage and uInitrd.
Minimal error checking is performed by the install and remove code.
This is an example of how the U-Boot directory should look after installing a kernel:
-rwxr-xr-x 1 root root 20632 May 5 10:15 MLO -rwxr-xr-x 1 root root 240 May 16 13:02 boot.cmd -rwxr-xr-x 1 root root 312 May 16 13:05 boot.scr -rwxr-xr-x 1 root root 112 Jun 1 18:12 klist.txt -rwxr-xr-x 1 root root 146536 May 5 10:16 u-boot.bin -rwxr-xr-x 1 root root 3934012 Jun 1 18:12 uImage -rwxr-xr-x 1 root root 3934012 Jun 1 18:12 uImage-18.104.22.168-31.01.fc13.armv7l.omap -rwxr-xr-x 1 root root 8476083 Jun 1 18:12 uInitrd -rwxr-xr-x 1 root root 8476083 Jun 1 18:12 uInitrd-22.214.171.124-31.01.fc13.armv7l.omap
This is an example of the autoboot command file (boot.cmd) for the Panda board:
setenv bootargs console=ttyO2,115200n8 ro rootwait root=/dev/mmcblk0p4 init=/sbin/init earlyprintk rd_NO_PLYMOUTH setenv bootcmd 'mmc init; fatload mmc 0:1 0x80300000 uImage; fatload mmc 0:1 81600000 uInitrd; bootm 80300000 81600000' boot
Your command options may vary, depending on your specific configuration, but the uImage and uInitrd files must be used for this method to work.
This file can be converted to the autoboot script (boot.scr) using the following command:
mkimage -A arm -O linux -T script -C none -a 0 -e 0 -n "PandaBoard boot script" -d boot.cmd boot.scr
The name of the U-Boot directory, the device partition used, the name of the installed kernel version list, and the image file names used are all configurable through the
/etc/sysconfig/uboot file. The defaults are provided:
UBOOT_DIR=/boot/uboot UBOOT_DEVICE=mmcblk0p1 UBOOT_KLIST=klist.txt UBOOT_UIMAGE=uImage UBOOT_UINITRD=uInitrd
Set Up the Repository
- get the eXtra Packages for Fedora ARM (xpfa) yum repository definition:
sudo yum --nogpgcheck install http://dmarlin.fedorapeople.org/packages/FedoraArm/RPMS/noarch/xpfa-13-1.noarch.rpm
- update grubby to get the modified version:
sudo yum --enablerepo=xpfa update grubby
- make any changes to the U-Boot configuration (if needed):
sudo vi /etc/sysconfig/uboot
Install the Kernel
- install the latest ARM OMAP kernel version:
sudo yum --enablerepo=xpfa update linux-firmware sudo yum --enablerepo=xpfa install kernel-omap
If all goes well, the latest kernel-omap version should installed, the U-Boot images copied to the default U-Boot image files, and the latest kernel-omap version appended to the installed kernel version list file (klist.txt). On the next reboot, the new kernel version should be booted automatically.
- A first attempt has been made to split up the config file like other Fedora architures (generic, arch-generic, board). Currently this kernel uses config-generic, config-arm-generic, and config-omap-generic to produce the merged armv7l-omap config. These need to be further refined to ensure the correct division between arm-generic and omap-generic.
- The ARM config options should be reviewed to make sure they are appropriate for the current kernel version.
- Support for other ARM variants and boards could be added (other kernel variants).