Architectures/Fedora ARM Kernels

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-.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.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)

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.

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-2.6.38.8-31.01.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-2.6.38.8-31.01.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  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
sudo yum --nogpgcheck install http://dmarlin.fedorapeople.org/packages/FedoraArm/RPMS/noarch/xpfa-13-1.noarch.rpm sudo yum --enablerepo=xpfa update grubby sudo vi /etc/sysconfig/uboot
 * get the eXtra Packages for Fedora ARM (xpfa) yum repository definition:
 * update grubby to get the modified version:
 * make any changes to the U-Boot configuration (if needed):

Install the Kernel
sudo yum --enablerepo=xpfa update linux-firmware sudo yum --enablerepo=xpfa install kernel-omap
 * install the latest ARM OMAP kernel version:

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
sudo yum --nogpgcheck install http://dmarlin.fedorapeople.org/packages/FedoraArm/RPMS/noarch/xpfa-15-1.noarch.rpm sudo yum --enablerepo=xpfa update grubby sudo vi /etc/sysconfig/uboot
 * get the eXtra Packages for Fedora ARM (xpfa) yum repository definition:
 * update grubby to get the modified version:
 * make any changes to the U-Boot configuration (if needed):

Install the F15 Kernel

 * Install the latest kernel version:

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
 * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45819
 * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45704
 * patch from http://www.delorie.com/tmp/arm-readl.patch

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
 * patch from http://myplugbox.com/bunghole/linux-tegra/armdma.patch


 * 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).