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This article provides simple examples for the Distribution Package of the OpenSTLinux distribution, that illustrate the cross-compilation with the devtool and BitBake tools:
- modification with Linux® Kernel (configuration, device tree, driver, ...)
- modification of an external in-tree Linux Kernel module
- modification of U-Boot
- modification of TF-A
- addition of software
These examples also show how to deploy the results of the cross-compilation on the target, through a network connection to the host machine.
2. Prerequisites[edit source]
The prerequisites from Installing the OpenSTLinux distribution must be executed.
The board and the host machine are connected through an Ethernet link, and a remote terminal program is started on the host machine: see How to get Terminal.
The target is started, and its IP address (<board ip address>) is known.
3. Modification with kernel[edit source]
3.1. Preamble[edit source]
To start modification with a module, you need to initialize your Distribution Package environment.
cd <working directory path of distribution> DISTRO=openstlinux-weston MACHINE=stm32mp1 source layers/meta-st/scripts/envsetup.sh
You are now in the build directory, identified by <build dir> in the following paragraphs.
Initialize devtool for kernel component:
devtool modify virtual/kernel NOTE: Starting bitbake server... NOTE: Creating workspace layer in /mnt/internal_storage/oetest/oe_openstlinux_rocko/build-openstlinuxweston-stm32mp1/workspace NOTE: Enabling workspace layer in bblayers.conf Parsing recipes: 100% |########################################################################################| Time: 0:00:54 Parsing of 2401 .bb files complete (0 cached, 2401 parsed). 3282 targets, 88 skipped, 0 masked, 0 errors. NOTE: Mapping virtual/kernel to linux-stm32mp NOTE: Resolving any missing task queue dependencies ...
3.2. Modifying kernel configuration[edit source]
This simple example modifies the kernel configuration via menuconfig for the CMA size.
- Get the current value of the CMA size (128 Mbytes here) through the analysis of the target boot log
dmesg | grep -i cma [ 0.000000] cma: Reserved 128 MiB at 0xf0000000
- Start the Linux kernel configuration menu: see Menuconfig or how to configure kernel
- Navigate to "Device Drivers - Generic Driver Options"
- select "Size in Megabytes"
- modify its value to 256
- exit and save the new configuration
- Check that the configuration file (.config) has been modified
grep -i CONFIG_CMA_SIZE_MBYTES <build dir>/workspace/sources/<name of kernel recipe>/.config.new CONFIG_CMA_SIZE_MBYTES=256
- Cross-compile the Linux kernel: see Menuconfig or how to configure kernel
- Update the Linux kernel image on board: see Menuconfig or how to configure kernel
- Reboot the board: see Menuconfig or how to configure kernel
- Get the new value of the CMA size (256 Mbytes) through the analysis of the target boot log
dmesg | grep -i cma
[ 0.000000] cma: Reserved 256 MiB at 0xe0000000
3.3. Modifying the Linux kernel device tree[edit source]
This simple example modifies the default status of a user LED.
- With the board started; check that the user LED (LD3) is disabled
- Go to the <build dir>/workspace/sources/<name of kernel recipe>/ directory
cd <build dir>/workspace/sources/<name of kernel recipe>/
- Edit the arch/arm/boot/dts/stm32mp157c-ed1.dts Device Tree Source file for evaluation board or
Edit the arch/arm/boot/dts/stm32mp157c-dk2.dts Device Tree Source file for discovery board or
- Change the status of the "stm32mp:green:user" led to "okay", and set its default state to "on"
led {
compatible = "gpio-leds";
status = "okay";
red {
label = "stm32mp:red:status";
gpios = <&gpioa 13 GPIO_ACTIVE_LOW>;
status = "disabled";
};
green {
label = "stm32mp:green:user";
gpios = <&gpioa 14 GPIO_ACTIVE_LOW>;
default-state = "on";
status = "okay";
};
};
- Go to the build directory
cd <build dir>
If this update is accepted, then to report in other paragraph of this page}}
- Generate the device tree blobs (*.dtb)
bitbake virtual/kernel -C compile
- Update the device tree blobs on the board
scp <build dir>/tmp-glibc/deploy/images/<machine name>/*.dtb root@<board ip address>:/boot
- Reboot the board
cd /boot; sync; systemctl reboot
- Check that the user LED (LD3) is enabled (green)
3.4. Modifying a built-in Linux kernel device driver[edit source]
This simple example adds unconditional log information when the display driver is probed.
- Check that there is no log information when the display driver is probed
dmesg | grep -i stm_drm_platform_probe
- Go to the <build dir>/workspace/sources/<name of kernel recipe>/
cd <build dir>/workspace/sources/<name of kernel recipe>/
- Edit the ./drivers/gpu/drm/stm/drv.c source file
- Add a log information in the stm_drm_platform_probe function
static int stm_drm_platform_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct drm_device *ddev;
int ret;
[...]
DRM_INFO("Simple example - %s\n", __func__);
return 0;
[...]
}
- Go to the build directory
cd <build dir>
- Cross-compile the Linux kernel
bitbake virtual/kernel -C compile
- Update the Linux kernel image on board
scp <build dir>/tmp-glibc/deploy/images/<machine name>/uImage root@<board ip address>:/boot
- Reboot the board
cd /boot; sync; systemctl reboot
- Check that there is now log information when the display driver is probed
dmesg | grep -i stm_drm_platform_probe
[ 5.005833] [drm] Simple example - stm_drm_platform_probe
3.5. Modifying/adding an external Linux kernel module[edit source]
Most device drivers (modules) in the Linux kernel can be compiled either into the kernel itself (built-in/internal module) or as Loadable Kernel Modules (LKM/external module) that need to be placed in the root file system under the /lib/modules directory. An external module can be in-tree (in the kernel tree structure), or out-of-tree (outside the kernel tree structure).
This simple example adds an unconditional log information when the virtual video test driver (vivid) kernel module is probed or removed.
- Go to the <build dir>/workspace/sources/<name of kernel recipe>/
cd <build dir>/workspace/sources/<name of kernel recipe>/
- Edit the ./drivers/media/platform/vivid/vivid-core.c source file
- Add log information in the vivid_probe and vivid_remove functions
static int vivid_probe(struct platform_device *pdev)
{
const struct font_desc *font = find_font("VGA8x16");
int ret = 0, i;
[...]
/* n_devs will reflect the actual number of allocated devices */
n_devs = i;
pr_info("Simple example - %s\n", __func__);
return ret;
}
static int vivid_remove(struct platform_device *pdev)
{
struct vivid_dev *dev;
unsigned int i, j;
[...]
pr_info("Simple example - %s\n", __func__);
return 0;
}
- Go to the build directory
cd <build dir>
- Cross-compile the Linux kernel modules
bitbake virtual/kernel -C compile
- Update the vivid kernel module on the board
devtool deploy-target -Ss <name of kernel recipe> root@<board ip address>:/
- Update dependency descriptions for loadable kernel modules, and synchronize the data on disk with memory
/sbin/depmod -a sync
- Insert the vivid kernel module into the Linux kernel
modprobe vivid
[...]
[ 3412.784638] Simple example - vivid_probe
- Remove the vivid kernel module from the Linux kernel
rmmod vivid
[...]
[ 3423.708517] Simple example - vivid_remove
4. Adding an external out-of-tree Linux kernel module[edit source]
This simple example adds a "Hello World" external out-of-tree Linux kernel module to the Linux kernel.
- Create a directory for this kernel module example
mkdir kernel_module_example cd kernel_module_example
- Create the source code file for this kernel module example: kernel_module_example.c
// SPDX-identifier: GPL-2.0
/*
* Copyright (C) STMicroelectronics SA 2018
*
* Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
*
*/
#include <linux/module.h> /* for all kernel modules */
#include <linux/kernel.h> /* for KERN_INFO */
#include <linux/init.h> /* for __init and __exit macros */
static int __init kernel_module_example_init(void)
{
printk(KERN_INFO "Kernel module example: hello world from STMicroelectronics\n");
return 0;
}
static void __exit kernel_module_example_exit(void)
{
printk(KERN_INFO "Kernel module example: goodbye from STMicroelectronics\n");
}
module_init(kernel_module_example_init);
module_exit(kernel_module_example_exit);
MODULE_DESCRIPTION("STMicroelectronics simple external out-of-tree Linux kernel module example");
MODULE_AUTHOR("Jean-Christophe Trotin <jean-christophe.trotin@st.com>");
MODULE_LICENSE("GPL v2");
- Create the makefile for this kernel module example: Makefile
# Makefile for simple external out-of-tree Linux kernel module example # Object file(s) to be built obj-m := kernel_module_example.o # Path to the directory that contains the Linux kernel source code # and the configuration file (.config) KERNEL_DIR ?= <Linux kernel path> # Path to the directory that contains the source file(s) to compile PWD := $(shell pwd) default: $(MAKE) -C $(KERNEL_DIR) M=$(PWD) modules clean: $(MAKE) -C $(KERNEL_DIR) M=$(PWD) clean
- Add a new recipe to the workspace
cd <build dir> devtool add mymodule kernel_module_example/
- Adapt recipe to kernel module build
devtool edit-recipe mymodule
- Modify the recipe according the following changes (see highlighted lines)
# Recipe created by recipetool
# This is the basis of a recipe and may need further editing in order to be fully functional.
# (Feel free to remove these comments when editing.)
# Unable to find any files that looked like license statements. Check the accompanying
# documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
#
# NOTE: LICENSE is being set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (it
# will not be in most cases) you must specify the correct value before using this
# recipe for anything other than initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""
# No information for SRC_URI yet (only an external source tree was specified)
SRC_URI = ""
# NOTE: this is a Makefile-only piece of software, so we cannot generate much of the
# recipe automatically - you will need to examine the Makefile yourself and ensure
# that the appropriate arguments are passed in.
DEPENDS = "virtual/kernel"
inherit module
EXTRA_OEMAKE = "ARCH=arm"
EXTRA_OEMAKE += "KERNEL_DIR=${STAGING_KERNEL_BUILDDIR}"
S = "${WORKDIR}"
do_configure () {
# Specify any needed configure commands here
:
}
do_compile () {
# You will almost certainly need to add additional arguments here
oe_runmake
}
do_install () {
# NOTE: unable to determine what to put here - there is a Makefile but no
# target named "install", so you will need to define this yourself
install -d ${D}/lib/modules/${KERNEL_VERSION}
install -m 0755 ${B}/kernel_module_example.ko ${D}/lib/modules/${KERNEL_VERSION}/
}
- Go to the build directory
cd <build dir>
- Generated kernel module example
devtool build mymodule
- Push this kernel module example on board
devtool deploy-target -Ss mymodule root@<board ip address>
- Update dependency descriptions for loadable kernel modules, and synchronize the data on disk with memory
/sbin/depmod -a sync
- Insert the kernel module example into the Linux kernel
modprobe kernel_module_example
[18167.821725] Kernel module example: hello world from STMicroelectronics
- Remove the kernel module example from the Linux kernel
rmmod kernel_module_example
[18180.086722] Kernel module example: goodbye from STMicroelectronics
5. Modifying the U-Boot[edit source]
This simple example adds unconditional log information when U-Boot starts. Within the scope of the trusted boot chain, U-Boot is used as second stage boot loader (SSBL).
- Have a look at the U-Boot log information when the board reboots
reboot [...] U-Boot <U-Boot version> CPU: STM32MP1 rev1.0 Model: STMicroelectronics STM32MP157C [...] Board: stm32mp1 in trusted mode [...]
- Go to the build directory
cd <build dir>
- Search U-boot recipe
devtool search u-boot* u-boot-stm32mp-extlinux Generate 'extlinux.conf' file for U-boot u-boot-stm32mp Universal Boot Loader for embedded devices for stm32mp
On this example, the recipe name is u-boot-stm32mp
- Start to work with u-boot
devtool modify u-boot-stm32mp
Example: cd <build dir>/workspace/sources/u-boot-stm32mp
- Edit the ./board/st/stm32mp1/stm32mp1.c source file
- Add a log information in the checkboard function
int checkboard(void)
{
char *mode;
[...]
printf("Board: stm32mp1 in %s mode\n", mode);
printf("U-Boot simple example\n");
return 0;
}
- Cross-compile the U-Boot: trusted boot
devtool build u-boot-stm32mp bitbake u-boot-stm32mp -c deploy
- Go to the directory in which the compilation results are stored
cd <build dir>/tmp-glibc/deploy/images/<machine name>/
- Reboot the board, and hit any key to stop in the U-boot shell
reboot [...] Hit any key to stop autoboot: 0 STM32MP>
- Connect a USB cable between the host machine and the board via the USB OTG ports
- In the U-Boot shell, call the USB mass storage function
STM32MP> ums 0 mmc 0
- On the host machine, check the partition associated with the secondary stage boot loader (ssbl): sdc3 here
ls -l /dev/disk/by-partlabel/
total 0
lrwxrwxrwx 1 root root 10 Jan 17 18:05 bootfs -> ../../sdc4
lrwxrwxrwx 1 root root 10 Jan 17 18:05 fsbl1 -> ../../sdc1
lrwxrwxrwx 1 root root 10 Jan 17 18:05 fsbl2 -> ../../sdc2
lrwxrwxrwx 1 root root 10 Jan 17 18:05 rootfs -> ../../sdc5
lrwxrwxrwx 1 root root 10 Jan 17 18:05 ssbl -> ../../sdc3
lrwxrwxrwx 1 root root 10 Jan 17 18:05 userfs -> ../../sdc6
- Copy the binary (u-boot.stm32) to the dedicated partition
dd if=u-boot-<board name>-trusted.stm32 of=/dev/sdc3 bs=1M conv=fdatasync
(here u-boot-stm32mp157c-ev1-trusted.stm32 or u-boot-stm32mp157c-dk2-trusted.stm32)
- Reset the U-Boot shell
STM32MP> reset
- Have a look at the new U-Boot log information when the board reboots
[...] U-Boot <U-Boot version> CPU: STM32MP1 rev1.0 Model: STMicroelectronics STM32MP157C [...] Board: stm32mp1 in trusted mode U-Boot simple example [...]
6. Modifying the TF-A[edit source]
This simple example adds unconditional log information when the TF-A starts. Within the scope of the trusted boot chain, TF-A is used as first stage boot loader (FSBL).
- Have a look at the TF-A log information when the board reboots
reboot [...] INFO: System reset generated by MPU (MPSYSRST) INFO: Using SDMMC [...]
- Go to the build directory
cd <build dir>
- Search TF-A recipe
devtool search tf-a*
babeltrace Babeltrace - Trace Format Babel Tower
libunistring Library for manipulating C and Unicode strings
lttng-tools Linux Trace Toolkit Control
gettext Utilities and libraries for producing multi-lingual messages
glibc GLIBC (GNU C Library)
tf-a-stm32mp Trusted Firmware-A for STM32MP1
gnutls GNU Transport Layer Security Library
gstreamer1.0 GStreamer 1.0 multimedia framework
harfbuzz Text shaping library
glibc-locale Locale data from glibc
kbd Keytable files and keyboard utilities
On this example, the recipe name is tf-a-stm32mp
- Start to work with tf-a
devtool modify tf-a-stm32mp
- Go to <build dir>/workspace/sources/tf-a-stm32mp
cd <build dir>/workspace/sources/tf-a-stm32mp
- Edit the ./plat/st/stm32mp1/bl2_io_storage.c source file
- Add a log information in the stm32mp1_io_setup function
void stm32mp1_io_setup(void)
{
int io_result;
[...]
/* Add a trace about reset reason */
print_reset_reason();
INFO("TF-A simple example");
[...]
}
- Cross-compile the TF-A
devtool build tf-a-stm32mp bitbake tf-a-stm32mp -c deploy
- Go to the directory in which the compilation results are stored
cd <build dir>/tmp-glibc/deploy/images/<machine name>/
- Reboot the board, and hit any key to stop in the U-boot shell
reboot [...] Hit any key to stop autoboot: 0 STM32MP>
- Connect a USB cable between the host machine and the board via the USB OTG ports
- In the U-Boot shell, call the USB mass storage function
STM32MP> ums 0 mmc 0
- On the host machine, check the partition associated with the first stage boot loader (fsbl1 and fsbl2 as backup): sdc1 and sdc2 (as backup) here
ls -l /dev/disk/by-partlabel/ total 0 lrwxrwxrwx 1 root root 10 Jan 17 18:05 bootfs -> ../../sdc4 lrwxrwxrwx 1 root root 10 Jan 17 18:05 sfsbl1 -> ../../sdc1 lrwxrwxrwx 1 root root 10 Jan 17 18:05 sfsbl2 -> ../../sdc2 lrwxrwxrwx 1 root root 10 Jan 17 18:05 rootfs -> ../../sdc5 lrwxrwxrwx 1 root root 10 Jan 17 18:05 ssbl -> ../../sdc3 lrwxrwxrwx 1 root root 10 Jan 17 18:05 userfs -> ../../sdc6
- Copy the binary (tf-a-stm32mp157c-ev1-trusted.stm32) to the dedicated partition; to test the new TF-A binary, it might be useful to keep the old TF-A binary in the backup FSBL (fsbl2)
dd if=tf-a-<board name>-trusted.stm32 of=/dev/sdc1 bs=1M conv=fdatasync
(here tf-a-stm32mp157c-ev1-trusted.stm32 or tf-a-stm32mp157c-dk2-trusted.stm32)
- Reset the U-Boot shell
STM32MP> reset
- Have a look at the new TF-A log information when the board reboots
[...] INFO: System reset generated by MPU (MPSYSRST) INFO: TF-A simple example INFO: Using SDMMC [...]
7. Adding a "hello world" user space example[edit source]
This chapter shows how to compile and execute a simple "hello world" example.
- Create a directory for this user space example
mkdir hello_world_example cd hello_world_example
- Create the source code file for this user space example: hello_world_example.c
// SPDX-identifier: GPL-2.0
/*
* Copyright (C) STMicroelectronics SA 2018
*
* Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
*
*/
#include <stdio.h>
#include <unistd.h>
int main(int argc, char **argv)
{
int i =11;
printf("\nUser space example: hello world from STMicroelectronics\n");
setbuf(stdout,NULL);
while (i--) {
printf("%i ", i);
sleep(1);
}
printf("\nUser space example: goodbye from STMicroelectronics\n");
return(0);
}
- Add a new recipe to the workspace
cd <build dir> devtool add myhelloword hello_world_example/
- Adapt recipe
devtool edit-recipe myhelloword
- Modify the recipe according the following changes (see highlighted lines)
# Recipe created by recipetool
# This is the basis of a recipe and may need further editing in order to be fully functional.
# (Feel free to remove these comments when editing.)
# Unable to find any files that looked like license statements. Check the accompanying
# documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
#
# NOTE: LICENSE is being set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (it
# will not be in most cases) you must specify the correct value before using this
# recipe for anything other than initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""
# No information for SRC_URI yet (only an external source tree was specified)
SRC_URI = ""
# NOTE: no Makefile found, unable to determine what needs to be done
do_configure () {
# Specify any needed configure commands here
:
}
do_compile () {
# Specify compilation commands here
cd ${S}
${CC} hello_world_example.c -o hello_word_example
}
do_install () {
# Specify install commands here
install -d ${D}${bindir}
install -m 755 ${S}/hello_word_example ${D}${bindir}/
}
- Compile binary
devtool build myhelloword
- Push this binary on board
devtool deploy-target -s myhelloword root@<board ip address>
- Execute this user space example
/usr/bin/hello_world_example User space example: hello world from STMicroelectronics 10 9 8 7 6 5 4 3 2 1 0 User space example: goodbye from STMicroelectronics
8. Tips[edit source]
8.1. Creating a mounting point[edit source]
The objective is to create a mounting point for the boot file system (bootfs partition)
- Find the partition label associated with the boot file system
ls -l /dev/disk/by-partlabel/
total 0
lrwxrwxrwx 1 root root 15 Dec 13 12:31 bootfs -> ../../mmcblk0p4
lrwxrwxrwx 1 root root 15 Dec 13 12:31 fsbl1 -> ../../mmcblk0p1
lrwxrwxrwx 1 root root 15 Dec 13 12:31 fsbl2 -> ../../mmcblk0p2
lrwxrwxrwx 1 root root 15 Dec 13 12:31 rootfs -> ../../mmcblk0p5
lrwxrwxrwx 1 root root 15 Dec 13 12:31 ssbl -> ../../mmcblk0p3
lrwxrwxrwx 1 root root 15 Dec 13 12:31 userfs -> ../../mmcblk0p6
- Attach the boot file system found under /dev/mmcblk0p4 in the directory /boot
mount /dev/mmcblk0p4 /boot