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Kernel Driver Backports Integration


Article updated at 02 Mar 2021
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For many off-the-shelf devices to work a suitable driver needs to be compiled into a custom Linux kernel. Not all such drivers are available in custom downstream Linux kernels in which case one can use the driver backports package including suitable drivers available from later Linux kernel versions.

In other words, backports allows the use of drivers from a newer kernel version on an older kernel version. For instance, we can use Wi-Fi drivers from mainline kernel release 4.19 into our NXP i.MX downstream based on 4.9.

Toradex provides a Git repository for backports: backports-toradex.git

Driver backports are available for the following subsystems:

  • Bluetooth
  • Ethernet
  • IEEE 802.15.4 (ZigBee & 6LoWPAN)
  • Media
  • NFC
  • Regulator
  • Wireless

Supported Embedded Linux BSP Releases

For the latest BSP releases of 2.8 and 3, Toradex added kernel driver backports to its demo images, therefore you may want to have a look at how to build our BSP from scratch using OpenEmbedded since the backports are already integrated there.

For BSP 5, backports are not required as of March 2021, but this can be changed if we identify such a need in the future, either from customer requests or new features and bug fixes.

How to Cross-Compile the Backports Drivers From Source

This section provides information on how to cross-compile the Wi-Fi backports. The instructions apply to other drivers/subsystems.

To enable support for driver backports a custom Linux kernel is required. Please refer to the following article concerning setup/compilation of the same:

Build U-Boot and Linux Kernel from Source Code

Remarks About L4T Linux Kernel

The L4T Linux kernel from NVIDIA is not based on top of a clean 3.1 kernel but rather some pre 3.2 version with further Android additions. The backports drivers integrated into the demo images already take that into consideration and have been tested with the L4T Linux kernel.

If manually building backports, one needs to disable the drivers/dependencies enabled in the L4T Linux kernel before cross-compiling the driver backports to avoid any conflicts.

For cross-compiling iwlwifi, it is necessary to disable the following configs in the L4T Linux kernel:

  • CONFIG_CFG80211

Then just compile and deploy the custom kernel as explained in the above-mentioned article.

Obtain the Toradex BSP Backports Version

The Toradex BSP uses a specific backports version and configuration. To use it, first, you have to find out the OpenEmbedded/Yocto Codename that corresponds to the BSP version you want to build the backports for. Check the table at the beginning of the OpenEmbedded (Core) article.

Attention: Only BSP 2.7 and 2.8 (plus downstream Apalis TK1 on BSP 3.0) support backports integration.

For instance:

  • For BSP 2.7, the <codename> is morty.
  • For BSP 2.8, the <codename> is rocko.

Clone the meta-toradex-bsp-common Yocto layer from Toradex using the codename above as branch:

$ cd ~
$ git clone -b <codename> git://

You can check the backports version and the corresponding name from the respective backports recipe name:

$ ls meta-toradex-bsp-common/recipes-kernel/backports/

For instance, as of 2019-december-11:

# For BSP 2.7 --> means backports from kernel 4.11

# For BSP 2.8 --> means backports from kernel 4.19

Note: Check your backports version since this will be referred later.

Obtain the Toradex BSP Backports Configuration

Copy the sample configuration file to your computer, temporarily. Then erase the meta-toradex-bsp-common, as you don't need it anymore,

$ cd ~
$ cp meta-toradex-bsp-common/recipes-kernel/backports/files/config ~/toradex-bsp
$ rm -rf meta-toradex-bsp-common

Note: This configuration is the one applied when you create an image through Yocto that uses any kind of backports drivers, and is the same across all modules. Instead of having separated configurations for both approaches (Outside Yocto and through Yocto), we decided to reduce this to the same to improve maintainability.

Fetch the Kernel Backports Source Code

Clone the backports Git repository, side-by-side with the Linux kernel repository, to your machine and checkout the corresponding remote branch that matches the backports version found in the previous section:

$ cd ~
$ git clone -b toradex-<backports version> git://

You should have the following directory structure:

$ ls | grep "*-toradex"

Create a directory for kernel module deployment, as described in Kernel Module Compilation, if not created already:

$ mkdir -p ~/linux-toradex/modules

We will refer to linux-toradex as <kernel-build-directory> and linux-toradex/modules as module-deployment-direcory.

Additional Setup on Top of the Kernel Compilation Setup

Export a few more environment variables in addition to the ones described here.

$ export KLIB=<module-deployment-direcory>
$ export KLIB_BUILD=<kernel-build-directory>

E.g. if you have cloned both the Linux kernel and backports to your home:

$ export KLIB=~/linux-toradex/modules
$ export KLIB_BUILD=~/linux-toradex

Install the Toradex BSP Default Configuration

Move the temporary toradex-bsp file to the defconfigs directory and load the Toradex BSP configuration:

$ cd ~
$ mv ~/toradex-bsp ~/backports-toradex/defconfigs/
$ cd backports-toradex
$ make defconfig-toradex-bsp

Note: Ignore any error messages that are printed to the command-line output.

Build the Backports

The 'make install' target isn't currently sane for cross-builds. In Makefile.real, there is a rule named install: modules. See for yourself:

$ grep -nre "install: modules" Makefile*
Makefile.real:91:install: modules

Remove the commands inside the rule install: modules that are after the modules_install command. See the diff below for reference:

$ git diff Makefile.real
diff --git a/Makefile.real b/Makefile.real
index 6550802..0fb1d20 100644
--- a/Makefile.real
+++ b/Makefile.real
@@ -92,11 +92,6 @@ install: modules
        @$(MAKE) -C $(KLIB_BUILD) M=$(BACKPORT_DIR)                     \
                INSTALL_MOD_DIR=$(KMODDIR) $(KMODPATH_ARG)              \
-       @./scripts/ $(KLIB)/ $(KLIB)/$(KMODDIR)
-       @./scripts/ $(KLIB)/$(KMODDIR)
-       @./scripts/
-       @/sbin/depmod -a
-       @./scripts/ $(KLIB)
        @echo Your backported driver modules should be installed now.
        @echo Reboot.

Build the modules and install to linux-toradex/modules:

$ make -j$(nproc) modules_install

Deploy the Backports

The compiled backports kernel modules are now in the directory linux-toradex/modules, presumably, the same directory that you have previously created while following the article Build the Linux Kernel from Source Code.

The kernel module deployment is covered in the Build U-Boot and Linux Kernel from Source Code documentation, under Kernel Module Deployment.

Optional - Additional Backports Configuration

With the above procedure you should be effectively using the same configuration that is applied to our backports through a Yocto compilation, enabling WiFi and Bluetooth capabilities to the respective modules.

However, one can use the nconfig or menuconfig options to further configure the driver backports package. Default configuration files are also available which can be used to build the drivers/subsystems. If you choose to use this option just use the make defconfig-option in replacement for make menuconfig.

$ make defconfig-help
Driver or subsystem configuration targets:

Note: For BSP 2.7 only defconfig-wifi (e.g. without Bluetooth) is available, which we removed in BSP 2.8 in favor of using the more homogeneous approach, that is explained in the main section of this page.


Most Wi-Fi hardware uses specific firmware to operate properly. Certain such firmware can easily be installed as follows:

# opkg update
# opkg --force-depends install linux-firmware

Intel 7260 mini-PCIe Wi-Fi module with backported iwlwifi driver on Apalis T30.

During boot one gets the following kernel messages:

[   13.801594] Loading modules backported from Linux version v3.11.8-0-g02709ef                                                                                      
[   13.849714] Backport generated by backports.git v3.11.8-1-0-gb22d1cd                                                                                              
[   14.638853] cfg80211: Calling CRDA to update world regulatory domain                                                                                              
[   15.068568] Intel(R) Wireless WiFi driver for Linux, in-tree:d                                                                                                    
[   15.076809] Copyright(c) 2003-2013 Intel Corporation                                                                                                              
[   15.171085] iwlwifi 0000:04:00.0: loaded firmware version op_mode iwlmvm                                                                                 
[   16.786565] iwlwifi 0000:04:00.0: Detected Intel(R) Wireless N 7260, REV=0x144                                                                                    
[   16.800739] iwlwifi 0000:04:00.0: L1 Disabled; Enabling L0S                                                                                                       
[   16.809894] iwlwifi 0000:04:00.0: L1 Disabled; Enabling L0S                                                                                                       
[   17.038502] Registered led device: phy0-led                                                                                                                       
[   18.410483] ADDRCONF(NETDEV_UP): enp7s0: link is not ready                                                                                                        
[   18.425138] ieee80211 phy0: Selected rate control algorithm 'iwl-mvm-rs'                                                                                          
[   18.493031] iwlwifi 0000:04:00.0: L1 Disabled; Enabling L0S                                                                                                       
[   18.498950] iwlwifi 0000:04:00.0: L1 Disabled; Enabling L0S                                                                                                       
[   18.544093] ADDRCONF(NETDEV_UP): wlp4s0: link is not ready                             
root@apalis-t30:~# uname -a
Linux apalis-t30 3.1.10-g54d69d3 #23 SMP PREEMPT Wed Jun 10 17:46:46 IST 2015 armv7l GNU/Linux
root@apalis-t30:~# ls /lib/modules/3.1.10-g54d69d3/
modules.alias        modules.dep          modules.softdep      updates
modules.alias.bin    modules.dep.bin      modules.symbols
modules.builtin.bin  modules.devname      modules.symbols.bin
root@apalis-t30:~# lsmod
Module                  Size  Used by
iwlmvm                150786  0 
mac80211              477632  1 iwlmvm
iwlwifi               153573  1 iwlmvm
cfg80211              439297  3 iwlwifi,mac80211,iwlmvm
compat                 24552  4 cfg80211,iwlwifi,mac80211,iwlmvm