Dev/Embedded/FromScratch/LinuxKernel - Revision history

Drizzt: /* Preamble : external build */

2025-01-14T13:56:44Z

Preamble : external build

← Older revision		Revision as of 15:56, 14 January 2025
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	It's usually a god idea to build the Linux kernel in a separate Build directory in order to keep the sources clean and allow you to run multiple builds using a single source tree, saving disk space and making it easier to spot what got compiled.		It's usually a god idea to build the Linux kernel in a separate Build directory in order to keep the sources clean and allow you to run multiple builds using a single source tree, saving disk space and making it easier to spot what got compiled.

	Let's suppose you have your sources in the "linux" directory then to setup the Build environment you should run the following commands (set the '''arch''' variable to the right value for your hardware) :		Let's suppose you have your sources in the "linux" directory, and an "example.config" config file then to setup the Build environment you should run the following commands (set the '''arch''' variable to the right value for your hardware) :
	mkdir -p Build/linux		mkdir -p Build/linux # Create the external build directory
	cd linux		cp example.config Build/linux/.config # Copy your example config file in your external build directory
	arch=		cd linux # Move to the sources
	make ARCH=${arch} -j8 O=../Build/linux/ ~~allnoconfig~~		arch= # Set this to your target processor architecture : any of the directory names under the "arch" directory
			make ARCH=${arch} -j8 O=../Build/linux/ oldconfig # You'll be prompted for new configuration choices
			cd ../Build/linux # Then move to the external build directory
			make ARCH=${arch} menuconfig # And run further make commands without the need to add "O=..."

	Note that "~~allnoconfig~~" can be replaced by "alldefconfig".		Note that if you don't have an example config file, then "oldconfig" can be replaced by "allnoconfig", "alldefconfig", or any "in-kernel" available "board_defconfig".

	You now have a kernel "Build" directory, and should run all further commands from this build directory in order to keep the sources clean.		You now have a kernel "Build" directory, and should run all further commands from this build directory in order to keep the sources clean.

Drizzt: /* Technical part */

2025-01-02T08:49:57Z

Technical part

← Older revision		Revision as of 10:49, 2 January 2025
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	==== Technical part ====		==== Technical part ====
	All the technical information about the device tree concepts can be found on the '''[https://elinux.org/Device_Tree_Usage Device Tree Usage page of elinux.org]''' as well as the '''[https://elinux.org/Device_Tree_Linux Linux kernel specific information]''', or directly in [https://www.devicetree.org/ the device tree specification] (hosted on github [https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.4 v0.4] along [https://github.com/devicetree-org other device tree tools]).		All the technical information about the device tree concepts can be found on the '''[https://elinux.org/Device_Tree_Usage Device Tree Usage page of elinux.org]''' as well as the '''[https://elinux.org/Device_Tree_Linux Linux kernel specific information]''', or directly in [https://www.devicetree.org/ the device tree specification] (hosted on github ([https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.4 link to tag v0.4]) along [https://github.com/devicetree-org other device tree tools]).

	You will also get information '''[https://www.kernel.org/doc/html/latest/devicetree/index.html from the pages dedicated to the device tree in the kernel documentation]'''.		You will also get information '''[https://www.kernel.org/doc/html/latest/devicetree/index.html from the pages dedicated to the device tree in the kernel documentation]'''.

Drizzt: /* What are device trees used for ? */

2025-01-02T08:48:45Z

What are device trees used for ?

← Older revision		Revision as of 10:48, 2 January 2025
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	Thus, the kernel image will include all the code required for the SoC support (can be reduced to the used interfaces of course), while the device tree holds the SoC configuration for each interface.		Thus, the kernel image will include all the code required for the SoC support (can be reduced to the used interfaces of course), while the device tree holds the SoC configuration for each interface.

	Once again, you will [https://elinux.org/Device_Tree_Reference#What_Is_Device_Tree find more information on the device tree pages of eLinux Wiki].		Once again, you will '''[https://elinux.org/Device_Tree_Reference#What_Is_Device_Tree find more information on the device tree pages of eLinux Wiki]'''.

	==== Technical part ====		==== Technical part ====

Drizzt: /* The device tree */

2025-01-02T08:48:24Z

The device tree

← Older revision		Revision as of 10:48, 2 January 2025
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	The solution came from a "Flattened Device Tree" data format which is derived from the OpenFirmware specifications, first used for PowerPC boards, and later on for ARM systems and other architectures.		The solution came from a "Flattened Device Tree" data format which is derived from the OpenFirmware specifications, first used for PowerPC boards, and later on for ARM systems and other architectures.

	You may [https://elinux.org/Device_Tree_What_It_Is find additional information here].		You may '''[https://elinux.org/Device_Tree_What_It_Is find additional information here]'''.

	==== What are device trees used for ? ====		==== What are device trees used for ? ====
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	==== Technical part ====		==== Technical part ====
	All the technical information about the device tree concepts can be found on the [https://elinux.org/Device_Tree_Usage Device Tree Usage page of elinux.org] as well as the [https://elinux.org/Device_Tree_Linux Linux kernel specific information].		All the technical information about the device tree concepts can be found on the '''[https://elinux.org/Device_Tree_Usage Device Tree Usage page of elinux.org]''' as well as the '''[https://elinux.org/Device_Tree_Linux Linux kernel specific information]''', or directly in [https://www.devicetree.org/ the device tree specification] (hosted on github [https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.4 v0.4] along [https://github.com/devicetree-org other device tree tools]).

	You will also get information [https://www.kernel.org/doc/html/latest/devicetree/index.html from the pages dedicated to the device tree in the kernel documentation].		You will also get information '''[https://www.kernel.org/doc/html/latest/devicetree/index.html from the pages dedicated to the device tree in the kernel documentation]'''.

	==== Practical part ====		==== Practical part ====

Drizzt: /* Modules */

2024-12-30T01:34:15Z

Modules

← Older revision		Revision as of 03:34, 30 December 2024
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	You must copy the whole directory (not only the content) on the SD card, most probably in the partition holding the root filesystem (rootfs), in the /lib/modules/ directory without changing the name.<br />		You must copy the whole directory (not only the content) on the SD card, most probably in the partition holding the root filesystem (rootfs), in the /lib/modules/ directory without changing the name.<br />
	It could go to another partition, but then you'll need to make sure that all the drivers to access this partition are built inside the main kernel image.		It could go to another partition, but then you'll need to make sure that all the drivers to access this partition are built inside the main kernel image.

			== Next ==
			* Back to [[Dev/Embedded/FromScratch\|"From Scratch" page]].
			* Move to [[Dev/Embedded/Rootfs\|the rootfs part]] (though you should go on reading [[Dev/Embedded/FromScratch#UserLand\|the next step (UserLand) from the "From Scratch" page]] if you came from there).

Drizzt: /* Modules */

2024-12-30T01:14:53Z

Modules

← Older revision		Revision as of 03:14, 30 December 2024
Line 138:		Line 138:
	Instead you'll need to specify the modules installation path by setting "INSTALL_MOD_PATH" :		Instead you'll need to specify the modules installation path by setting "INSTALL_MOD_PATH" :

			compiler_prefix=
			arch=
	make ARCH=${arch} -j8 CROSS_COMPILE=${compiler_prefix} modules_install INSTALL_MOD_PATH=../results/		make ARCH=${arch} -j8 CROSS_COMPILE=${compiler_prefix} modules_install INSTALL_MOD_PATH=../results/

Drizzt: /* Practical part */

2024-12-30T01:13:33Z

Practical part

← Older revision		Revision as of 03:13, 30 December 2024
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	* '''Compilation of device tree files :'''		* '''Compilation of device tree files :'''
	Compilation of device tree files is automatic when compiling the Linux kernel, but you may want to re-run the compilation, which is done using the following command if you want to avoid the overhead of checking the whole kernel for modifications :		Compilation of device tree files is automatic when compiling the Linux kernel, but you may want to re-run the compilation, which is done using the following command if you want to avoid the overhead of checking the whole kernel for modifications :
	compiler_prefix=		compiler_prefix=
	arch=		arch=
	make ARCH=${arch} -j8 CROSS_COMPILE=${compiler_prefix} dtbs		make ARCH=${arch} -j8 CROSS_COMPILE=${compiler_prefix} dtbs

	== Kernel Compilation ==		== Kernel Compilation ==

Drizzt: /* Compilation results */

2024-12-21T21:06:14Z

Compilation results

← Older revision		Revision as of 23:06, 21 December 2024
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	The image name depends on your architecture and target. Most of the time it is set according to your configuration and there's no additional step required, but in some specific situations you may need to run an additional tool to build the final image for your bootloader.<br />		The image name depends on your architecture and target. Most of the time it is set according to your configuration and there's no additional step required, but in some specific situations you may need to run an additional tool to build the final image for your bootloader.<br />
	This will be detailled on each board specific page (tough I actually have no boards/configurations where this is required, I've had to do it for some custom boards).		This will be detailled on each board specific page (tough I actually have no boards/configurations where this is required, I've had to do it for some custom boards).

			This image file (your kernel binary) will then need to be loaded by your bootloader, so the next steps with this depends on your boatloarder, your board, and the chosen boot procedure.

	=== Device tree ===		=== Device tree ===
	The binary version of the device-tree is to be found under "arch/${arch}/boot/dts/".<br />		The binary version of the device-tree is to be found under "arch/${arch}/boot/dts/".<br />
	There's usually more than one compiled even with only one SoC selected in the configuration, so you'll have to pick the right one for your board.		There's usually more than one compiled even with only one SoC selected in the configuration, so you'll have to pick the right one for your board.

			This binary device tree file will also need to be loaded by your bootloader, so it usually goes somewhere close to the Linux kernel image in about the same way, which also depends on your boatloarder, your board, and the chosen boot procedure.

	=== Modules ===		=== Modules ===

Drizzt: /* Compilation results */

2024-12-21T21:01:00Z

Compilation results

← Older revision		Revision as of 23:01, 21 December 2024
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	== Compilation results ==		== Compilation results ==
	=== Linux Kernel ===		=== Linux Kernel ===
	Compilation result is in arch/~~arm~~/boot/~~Image~~		Compilation result is in "arch/${arch}/boot/"<br />
			The image name depends on your architecture and target. Most of the time it is set according to your configuration and there's no additional step required, but in some specific situations you may need to run an additional tool to build the final image for your bootloader.<br />
			This will be detailled on each board specific page (tough I actually have no boards/configurations where this is required, I've had to do it for some custom boards).

	=== Device tree ===		=== Device tree ===
	~~Use~~ the ~~sun8i-h2-plus-orangepi-zero.dtb~~ device-tree (found in arch/~~arm~~/boot/dts/~~) or sun8i-h2-plus-orangepi-zero-ed3l.dtb from my [http://data~~.~~nathael.net~~/~~Dev/OPi/OPiZero/ shared ressources]~~.		The binary version of the device-tree is to be found under "arch/${arch}/boot/dts/".<br />
			There's usually more than one compiled even with only one SoC selected in the configuration, so you'll have to pick the right one for your board.

	=== Modules ===		=== Modules ===
			If you have activated the modules support in your kernel configuration (which is usually the default) and selected some services or drivers to be compiled as modules, then you will need to install them.

			But usually, when building the kernel for an embedded system, your kernel sources are not on the target machine, so the default "make modules_install" cannot be used (it would install your target's modules on your host development system).
			Instead you'll need to specify the modules installation path by setting "INSTALL_MOD_PATH" :

	make ARCH=${arch} -j8 CROSS_COMPILE=${compiler_prefix} modules_install INSTALL_MOD_PATH=../results/		make ARCH=${arch} -j8 CROSS_COMPILE=${compiler_prefix} modules_install INSTALL_MOD_PATH=../results/

	If the compilation has been performed using the above command lines you should have a directory "Build/~~Mods~~/lib/modules/*" (* = name of the kernel you just compiled)~~<br />~~		If the compilation has been performed using the above command lines you should have a directory "Build/results/lib/modules/*" (* = name of the kernel you just compiled).
	You must copy the whole directory (not only the content) on the SD card, in the partition holding the root filesystem (rootfs), in the /lib/modules/ directory without changing the name.
			You must copy the whole directory (not only the content) on the SD card, most probably in the partition holding the root filesystem (rootfs), in the /lib/modules/ directory without changing the name.<br />
			It could go to another partition, but then you'll need to make sure that all the drivers to access this partition are built inside the main kernel image.

Drizzt at 13:55, 21 December 2024

2024-12-21T13:55:28Z

@@ Line 1: / Line 1: @@
 == Introduction ==
 For the Linux kernel, you usually have two (sometimes three) choices :
 * Get the official "vanilla" kernel from kernel.org
@@ Line 7: / Line 21: @@
 If you have some time available, then you can try to port the patches from the custom kernel to the official one and have them included in the upstream official kernel, which will always be greatly appreciated, though the hardest part of this is not the technical part (effective porting of the patches) but getting them accepted upstream.
 When getting the source from kernel.org you can use either git, or download an archive from kernel.org (which will lack git history but be smaller, both for download and for disk space)
   git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
@@ Line 16: / Line 29: @@
 It is also time to add any patch you received on top of your source tree in order to add any specific support which is not included in the cloned or extracted kernel sources.
 == Kernel Configuration ==
 It's usually a god idea to build the Linux kernel in a separate Build directory in order to keep the sources clean and allow you to run multiple builds using a single source tree, saving disk space and making it easier to spot what got compiled.