.. _play-kernel-development: BeaglePlay Kernel Development ############################# This guide is for all those who want to kick start their kernel development journey on the TI AM625x SoC Based BeaglePlay. Getting the Kernel Source Code ****************************** The Linux kernel is hosted on a number of servers around the world. The main repository is hosted on the kernel.org website, but there are also mirrors hosted by other organizations, such as GitHub and Bootlin. The `Linux Torvalds tree `_ is the most up-to-date source of the Linux kernel. It is used by Linux distributions and other projects to build their own kernels. The tree is also a popular destination for kernel developers who want to contribute to the kernel. Kernel sources can directly be fetched using ``git``: .. code-block:: bash git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git A big advantage of using ``git`` to fetch the kernel sources is that you'll easily be able to manage your changes, keeping track of what you might edit. If you are looking for a quicker way to download a single version of the Linux kernel sources to get started, you might consider fetching a "tarball" using ``wget``. .. code-block:: bash wget https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/snapshot/linux-6.6.tar.gz tar xf linux-6.6.tar.gz .. note:: While fetching a tarball with ``wget`` might be faster than fetching the full history with ``git``, the ability to track changes with ``git`` is significant. For more information on using ``git``, see :ref:`beagleboard-git-usage`. Preparing to Build ****************** These instructions should be valid on any Debian-based system, but were tested on a BeaglePlay itself. .. code-block:: bash sudo apt update sudo apt install -y fakeroot build-essential libncurses-dev xz-utils libssl-dev flex libelf-dev bison debhelper Configuring the Kernel ********************** The easiest way to configure the kernel is to start with a configuration known to work. A running BeaglePlay is a great source for that configuration, as it gets compiled into the running kernel. .. note:: If you don't have a BeaglePlay booted, you can copy a known good kernel configuration from the BeagleBoard.org Linux git repository at https://git.beagleboard.org/beagleboard/linux. On each release branch, the last commit typically contains a ``bb.org_defconfig`` file. For BeaglePlay, you should look for an ``arm64`` branch. Example: https://git.beagleboard.org/beagleboard/linux/-/blob/f47f74d11b19d8ae2f146de92c258f40e0930d86/arch/arm64/configs/bb.org_defconfig Running on a BeaglePlay, you can configure your kernel using ``/proc/config.gz``. You'll also want to ``make olddefconfig`` to update your config for the newer kernel. If you want to look at configuration options that haven't previously been configured, then use ``make oldconfig`` instead. Once you've got an initial configuration, you can edit the configuration various ways including ``make menuconfig``. .. code-block:: bash cd linux-6.6 zcat /proc/config.gz > .config make olddefconfig You can also take advantage of the running system to provide the WiFi regulatory database (regulatory.db). This is needed such that your kernel sets the WiFi signals appropriately for compliance with regional restrictions. For more information, see `Linux wireless regulatory documentation `_ and the signed database images at https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/tree/. .. code-block:: bash mkdir -p firmware cp /lib/firmware/regulatory.db* firmware/ Building the Kernel ******************* Once you're set on your configuration, you'll want to build the kernel and build any external modules. To make things simpler to install, we'll create a Debian package of the kernel. .. note:: Building the kernel on BeaglePlay might take a while. For me, it took about an hour. .. code-block:: bash cd .. make -C ./linux-6.6 -j4 KDEB_PKGVERSION=1xross bindeb-pkg Installing and Booting the Kernel ********************************* .. important:: In case your new kernel fails, you'll want to be prepared to either reflash the board or to use a serial cable to halt u-boot and request loading a working kernel still available on the board. See :ref:`beagleplay-serial-console` to setup access over the debug serial port. .. _play-dpkg-install-kernel: .. code-block:: bash :caption: Install 6.6.0 kernel and reboot sudo dpkg -i linux-image-6.6.0_1xross_arm64.deb sudo shutdown -r now As long as the kernel you built has no significant issues, you'll boot back into a running system. If there was a boot or connectivity failure, you can try an alternate connectivity method, such as the :ref:`beagleplay-serial-console` or Ethernet, or you can reflash the board and try again from a known good kernel source. For me, the linux-6.6 kernel booted fine, but the beagleplay.local (mDNS/Avahi broadcast) address did not show up right away. I was able to find the BeaglePlay hosted WiFi access point, the connection to my local WiFi network, connect over Ethernet and connect over USB network. The `/dev/play` directory did not exist, but the `/dev/bone` directory did, so this gives me a good starting point for generating some patches to update the mainline kernel. :-D See :ref:`beagleboard-linux-upstream` for more next steps by providing updates you make to the kernel to the upstream repository for everyone to benefit and for you to benefit from on future kernel versions. Kernel Debug ************ Consider reading the kernel documentation on `debugging via gdb `_. Also, consider the the TI Linux Board Porting Series, specifically the module on `debugging with JTAG in CCS `_. References ********** - To understand more about booting code on BeaglePlay, see :ref:`play-understanding-boot`. - For more details on the Linux kernel build system, see `The kernel build system `_ on kernel.org. - For additional guidance, see the `official TI-SDK documentation for AM62X `_