Architectures/Fedora ARM Kernels
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Building and Installing a Fedora Kernel Package on ARM Systems
This was originally written for Fedora 13. If you are already familiar with the concepts discussed and are only interesting in Fedora 15, you can skip to Set Up the F15 Repository.
This page is largely obsolete, as the Fedora ARM kernels are now being built in ARM Koji, and can be updated via yum. The grubby changes have also been pushed upstream and are available in F17 and newer. For F15, please use the patched version of grubby from the xpfa repository, as mentioned above.
Goal
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-2.6.40.3-0.fc15.
Kernel Version
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 and Tegra specific support, and applicable kernel config files were added. The kernel packages were then built for F13 on a Panda board using the following command:
rpmbuild -ba --target=armv7l SPECS/kernel.spec
The source and binary packages are available via yum:
http://dmarlin.fedorapeople.org/yum/f13/
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
These sources are also available in the upstream Fedora kernel.
If you are setup to use the Fedora ARM Koji Build System, a scratch build can be performed using:
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.
Issues
- 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
Assumptions
- U-Boot will use an autoboot script (
boot.scruEnv.txt) - The kernel will boot using an initrd
- The U-Boot partition (vfat) will be mounted on
/boot/uboot - the default boot images will use standard named files (i.e. uImage, uInitrd)
Approach
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.
The U-Boot directory may not always be mounted, since it is not required once Linux is booted. If the U-Boot partition is not already mounted, grubby will attempt to mount it and proceed. If grubby performs the mount, the partition will be unmounted when the process is complete (left in the same state as before the transaction).
This is an example of how the U-Boot directory should look after installing a kernel:
-rwxr-xr-x. 1 root root 506 Jun 18 16:51 armhfp-panda-xfce-mmcblk0-mmc-uEnv.txt -rwxr-xr-x. 1 root root 506 Jun 18 16:51 armhfp-panda-xfce-mmcblk0-usb-uEnv.txt -rwxr-xr-x. 1 root root 71 Jun 18 16:51 boot.scr -rwxr-xr-x. 1 root root 26 Jun 18 16:58 klist.txt -rwxr-xr-x. 1 root root 34152 Apr 24 13:53 MLO -rwxr-xr-x. 1 root root 260 Jun 18 16:51 README.txt -rwxr-xr-x. 1 root root 238068 Apr 24 13:53 u-boot.img -rwxr-xr-x. 1 root root 506 Jun 18 16:51 uEnv.txt -rwxr-xr-x. 1 root root 3974848 Jun 18 16:57 uImage-3.4.2-3.fc17.armv7hl.omap -rwxr-xr-x. 1 root root 3974848 Jun 18 16:57 uImage-omap -rwxr-xr-x. 1 root root 11742382 Jun 18 16:58 uInitrd-3.4.2-3.fc17.armv7hl.omap -rwxr-xr-x. 1 root root 11742382 Jun 18 16:58 uInitrd-omap
This is an example of the autoboot command file (boot.cmd) for the Pandaboard:
bootfile=uImage-omap
bootinitrd=uInitrd-omap
boot=bootm
address_image=0x80300000
address_initrd=0x81600000
mmcroot=LABEL=rootfs ro
mmcargs=setenv bootargs root=${mmcroot} init=/sbin/init quiet rootwait rhgb earlyprintk
loaduimage=run xyz_mmcboot; run mmcargs; ${boot} ${address_image} ${address_initrd}
xyz_load_image=fatload mmc 0:1 ${address_image} ${bootfile}
xyz_load_initrd=fatload mmc 0:1 ${address_initrd} ${bootinitrd}
xyz_mmcboot=run xyz_load_image; run xyz_load_initrd; echo Booting from mmc ...
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 uEnv.txt 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, here is the config for Pandaboard:
UBOOT_DIR=/boot/uboot UBOOT_IMGADDR=0x80008000 UBOOT_KLIST=klist.txt UBOOT_DEVICE=mmcblk0p1 UBOOT_UIMAGE=uImage UBOOT_UINITRD=uInitrd-omap
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Please make any changes to this configuration before performing any kernel installation or removal. Changing these after a kernel has been installed may cause future attempts to install or remove kernels to fail. The most likely values to change are
UBOOT_DIR and/or UBOOT_DEVICE, since these are based on how your flash device is partitioned and mounted.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
The kernel installation may require several minutes (installing the kernel images, modules, creating the initramfs, and creating the U-Boot image files), and there is little feedback during the process.
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.
Set Up the F15 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-15-1.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 F15 Kernel
- Install the latest kernel version:
Be sure to install the correct kernel variant for your system.
sudo yum --enablerepo=xpfa install kernel-omap # for Panda
sudo yum --enablerepo=xpfa install kernel-tegra # for Trim Slice
Issues
We are currently carrying three patches that will probably not go upstream:
- arm-readl.patch - workaround for issue with gcc-4.6.x
Update: arm-readl.patch is not necessary if using gcc-4.6.1-9.fc15.0.arm4.armv7hl
- arm-2.6.40.3-dma.patch - workaround for DMA coherency issue on ARM SMP systems
- TEGRA-2.6.40.2-USB-SATA-hack.patch - workaround for disconnection of USB-SATA on TrimSlice
- patch from Compulab: http://gitorious.org/trimslice-kernel/trimslice-kernel/commit/437e615d22291f1822808715e4e016ef5cf043bd
- This merely prevents USB disconnect. Replace or remove as soon as practical.
To Do
- The current kernel config files have been split up like other Fedora architures (generic, arch-generic, board). Currently this kernel uses config-generic, config-arm-generic, and config-omap-generic or config-tegra to produce the merged kernel config. These need to be further refined to ensure the correct division between arm-generic and the board specific config settings.
- The ARM config options should be reviewed to make sure they are appropriate for the current kernel and Fedora versions.
- Support for other ARM variants and boards could be added (other kernel variants).
