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:
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.
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
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:
Then just compile and deploy the custom kernel as explained in the above-mentioned article.
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:
<codename> is morty.<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://git.toradex.com/meta-toradex-bsp-common.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
backports_4.11.bb --> means backports from kernel 4.11
# For BSP 2.8
backports_4.19.bb --> means backports from kernel 4.19
Note: Check your backports version since this will be referred later.
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.
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://git.toradex.com/backports-toradex.git
You should have the following directory structure:
$ ls | grep "*-toradex"
linux-toradex
backports-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.
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
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.
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) \
modules_install
- @./scripts/blacklist.sh $(KLIB)/ $(KLIB)/$(KMODDIR)
- @./scripts/compress_modules.sh $(KLIB)/$(KMODDIR)
- @./scripts/check_depmod.sh
- @/sbin/depmod -a
- @./scripts/update-initramfs.sh $(KLIB)
@echo
@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
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.
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:
defconfig-ar5523
defconfig-ath10k
defconfig-ath5k
defconfig-ath6kl
defconfig-ath9k
defconfig-ath9k-debug
defconfig-b43
defconfig-b43legacy
defconfig-brcmfmac
defconfig-brcmsmac
defconfig-carl9170
defconfig-cw1200
defconfig-hwsim
defconfig-iwlwifi
defconfig-rtlwifi
defconfig-wcn36xx
defconfig-wifi
defconfig-wil6210
defconfig-wwan
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 22.1.7.0 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
