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--- ass:labs-2025:03:tasks:02 [2025/08/06 18:03]
radu.mantu
+++ ass:labs-2025:03:tasks:02 [2026/07/15 15:00] (current)
florin.stancu [02. Enabling networking on iMX93]
@@ Line 1: / Line 1: @@
 ==== 02. Enabling networking on iMX93 ====
-Notice that the FRDM-iMX93 has two Ethernet ports. But if you boot your previous Buildroot distro and try to see the available network: ''ip link show'', notice that they are missing. Instead, you'll only have the loopback interface ''lo''.
+Notice that the FRDM-iMX93 has two Ethernet ports. But if you boot your previous Buildroot distro and try to see the available network: ''ip link show''.
 In this task, you will have to debug the problem and try to fix it or at least find a workaround that lets you use your network interface.
@@ Line 17: / Line 16: @@
     * Remember that on ARM, drivers are matched to devices based on their ''compatible'' string from the DTB
     * The driver must also have at least one of these strings written in its source files.
-Once you are done, enable the **iperf3**, **iproute2** and **ethtool** network packages in Buildroot and build them. The compilation should not take more than 1-2 minutes. Re-generate ''linux.itb'' and copy it to the board's eMMC.
-Connect to a colleague's board with an Ethernet cable. \\
-Use the ''ip'' command to **add** a static IP to your network interface (''man ip-address''). \\
-Then, use the ''iperf3'' tool to test the throughput and compare it to what **ethtool** advertises. \\
-Why is it not a full 1Gbps?
 <spoiler Hint #1>
@@ Line 44: / Line 36: @@
 Try spoofing the MAC address of [[https://gist.github.com/aallan/b4bb86db86079509e6159810ae9bd3e4|some vendor]].
 </spoiler>
+Once you are done, enable the **iperf3**, **iproute2** and **ethtool** network packages in Buildroot and build them. The compilation should not take more than 1-2 minutes. Re-generate ''linux.itb'' and copy it to the board's eMMC.
+Connect to a colleague's board with an Ethernet cable. \\
+Use the ''ip'' command to **add** a static IP to your network interface (''man ip-address''). \\
+Then, use the ''iperf3'' tool to test the throughput and compare it to what **ethtool** advertises. \\
+Why is it not a full 1Gbps?
+=== Bonus: solving the actual cause of the problem ===
+The steps above might seem a bit hackish... that's because they are a ugly HACK working around the real problem!
+And the real problem is: since the kernel was compiled with external modules (and they take ''~300MB''),
+they were not included inside the initial ramdisk (obviously, since it's less than ''80MB'')!
+Due to missing modules, the ethernet driver and its dependencies could not be properly initialized (actually, as we've debugged above, it's just missing its MAC address provider) and thus fails!
+The real solution would be to install the buildroot-obtained rootfs (or any other method, tbh.), together with the external kernel modules (usually sitting inside ''/var/modules/7.x'' -- your kernel version).
+This can be easily done by using the kernel's built-in install target:
+<code bash>
+# enter linux kernel source directory
+cd linux/
+# create a target directory where external modules will be installed
+mkdir -p "../linux-modules"
+# install the modules
+make ARCH=arm64 INSTALL_MOD_PATH="../linux-overlay" modules modules_install
+# explore it!
+ls -l ../linux-modules/lib/modules/*
+</code>
+Next, you will want to add the ''linux-modules'' directory into your Buildroot filesystem.
+Fortunately, this is the easiest thing: enter buildroot's ''menuconfig'', search for ''ROOTFS_OVERLAY'' configuration item and set it to the **absolute path** of your ''linux-modules'' created above.
+Do a ''make'' and voila! The rootfs archive will have a huge size (''>~350MB''), meaning we successfully added all available kernel modules.
+There is one problem remaining, though: the rootfs won't fit anymore inside the uImage / small FAT32 partition...
+So change of plans: delete the ''initrd'' node from ''linux.its'' (together with its ''ramdisk'' configuration node property) and rebuild the uImage.
+Next, on the second partition inside your disk image, you must unpack the ''rootfs.tar'' file outputted by buildroot. Simply use ''tar xf ./path/to/rootfs.tar -C /mnt/your-ext4-partition/'' (check out the provided ''mk-disk-image.sh'' script!).
+Still not finished: we need to add the following parameter to the kernel command line BEFORE booting Linux: ''root=/dev/mmcblk0p2''. This can be done inside u-boot, e.g., by using the ''setenv'' command:
+<code>
+# it's recommended to supply the whole cmdline value:
+setenv bootargs "console=ttyLP0,115200 earlycon,115200 root=/dev/mmcblk0p2 clk_ignore_unused"
+</code>
+Otherwise, the kernel will complain that it cannot find the root block device and panic.
+Check out the kernel boot log if you have any problems (it will also print its command line parameters it receives from the bootloader)!
+If you successfully do all of this, you should see both ''eth'' interfaces: first one is 100Mbps, the second one is 1Gbps!