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--- ass:labs-2025:03:tasks:02 [2025/08/06 15:28]
radu.mantu [02. Enabling networking on iMX93]
+++ ass:labs-2025:03:tasks:02 [2026/07/16 11:35] (current)
florin.stancu
@@ 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 18: / Line 17: @@
     * 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?
-<hidden>
 <spoiler Hint #1>
 This line from **dmesg** tells us why the Network Interface Controller (NIC) remains unavailable.
@@ Line 33: / Line 24: @@
 </code>
 </spoiler>
-</hidden>
-<hidden>
 <spoiler Hint #2>
 The driver can be found at ''linux/drivers/net/ethernet/freescale/fec_main.c''. \\
-There, the ``fec_get_mac()`` function will tell you how the driver gets the NIC's MAC address. \\
+There, the ''fec_get_mac()'' function will tell you how the driver gets the NIC's MAC address. \\
 Try to provide it via another means, other than through the eFuse protected by the EdgeLink Enclave (that doesn't work).
 </spoiler>
-</hidden>
-<hidden>
 <spoiler Hint #3>
 In ''linux/net/ethernet/eth.c'' look at the comments of the ''fwnode_get_mac_address()'' function. \\
@@ Line 49: / Line 36: @@
 Try spoofing the MAC address of [[https://gist.github.com/aallan/b4bb86db86079509e6159810ae9bd3e4|some vendor]].
 </spoiler>
-</hidden>
+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 rootwait 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!