Documentation/arm/arm.rst - kernel/common - Git at Google

 =======================
 ARM Linux 2.6 and upper
 =======================

     Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for
     updates.

 Compilation of kernel
 ---------------------

   In order to compile ARM Linux, you will need a compiler capable of
   generating ARM ELF code with GNU extensions.  GCC 3.3 is known to be
   a good compiler.  Fortunately, you needn't guess.  The kernel will report
   an error if your compiler is a recognized offender.

   To build ARM Linux natively, you shouldn't have to alter the ARCH = line
   in the top level Makefile.  However, if you don't have the ARM Linux ELF
   tools installed as default, then you should change the CROSS_COMPILE
   line as detailed below.

   If you wish to cross-compile, then alter the following lines in the top
   level make file::

     ARCH = <whatever>

   with::

     ARCH = arm

   and::

     CROSS_COMPILE=

   to::

     CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>

   eg.::

     CROSS_COMPILE=arm-linux-

   Do a 'make config', followed by 'make Image' to build the kernel
   (arch/arm/boot/Image).  A compressed image can be built by doing a
   'make zImage' instead of 'make Image'.


 Bug reports etc
 ---------------

   Please send patches to the patch system.  For more information, see
   http://www.arm.linux.org.uk/developer/patches/info.php Always include some
   explanation as to what the patch does and why it is needed.

   Bug reports should be sent to [email protected],
   or submitted through the web form at
   http://www.arm.linux.org.uk/developer/

   When sending bug reports, please ensure that they contain all relevant
   information, eg. the kernel messages that were printed before/during
   the problem, what you were doing, etc.


 Include files
 -------------

   Several new include directories have been created under include/asm-arm,
   which are there to reduce the clutter in the top-level directory.  These
   directories, and their purpose is listed below:

   ============= ==========================================================
    `arch-*`	machine/platform specific header files
    `hardware`	driver-internal ARM specific data structures/definitions
    `mach`	descriptions of generic ARM to specific machine interfaces
    `proc-*`	processor dependent header files (currently only two
 		categories)
   ============= ==========================================================


 Machine/Platform support
 ------------------------

   The ARM tree contains support for a lot of different machine types.  To
   continue supporting these differences, it has become necessary to split
   machine-specific parts by directory.  For this, the machine category is
   used to select which directories and files get included (we will use
   $(MACHINE) to refer to the category)

   To this end, we now have arch/arm/mach-$(MACHINE) directories which are
   designed to house the non-driver files for a particular machine (eg, PCI,
   memory management, architecture definitions etc).  For all future
   machines, there should be a corresponding arch/arm/mach-$(MACHINE)/include/mach
   directory.


 Modules
 -------

   Although modularisation is supported (and required for the FP emulator),
   each module on an ARM2/ARM250/ARM3 machine when is loaded will take
   memory up to the next 32k boundary due to the size of the pages.
   Therefore, is modularisation on these machines really worth it?

   However, ARM6 and up machines allow modules to take multiples of 4k, and
   as such Acorn RiscPCs and other architectures using these processors can
   make good use of modularisation.


 ADFS Image files
 ----------------

   You can access image files on your ADFS partitions by mounting the ADFS
   partition, and then using the loopback device driver.  You must have
   losetup installed.

   Please note that the PCEmulator DOS partitions have a partition table at
   the start, and as such, you will have to give '-o offset' to losetup.


 Request to developers
 ---------------------

   When writing device drivers which include a separate assembler file, please
   include it in with the C file, and not the arch/arm/lib directory.  This
   allows the driver to be compiled as a loadable module without requiring
   half the code to be compiled into the kernel image.

   In general, try to avoid using assembler unless it is really necessary.  It
   makes drivers far less easy to port to other hardware.


 ST506 hard drives
 -----------------

   The ST506 hard drive controllers seem to be working fine (if a little
   slowly).  At the moment they will only work off the controllers on an
   A4x0's motherboard, but for it to work off a Podule just requires
   someone with a podule to add the addresses for the IRQ mask and the
   HDC base to the source.

   As of 31/3/96 it works with two drives (you should get the ADFS
   `*configure` harddrive set to 2). I've got an internal 20MB and a great
   big external 5.25" FH 64MB drive (who could ever want more :-) ).

   I've just got 240K/s off it (a dd with bs=128k); thats about half of what
   RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting
   last week :-)

   Known bug: Drive data errors can cause a hang; including cases where
   the controller has fixed the error using ECC. (Possibly ONLY
   in that case...hmm).


 1772 Floppy
 -----------
   This also seems to work OK, but hasn't been stressed much lately.  It
   hasn't got any code for disc change detection in there at the moment which
   could be a bit of a problem!  Suggestions on the correct way to do this
   are welcome.


 `CONFIG_MACH_` and `CONFIG_ARCH_`
 ---------------------------------
   A change was made in 2003 to the macro names for new machines.
   Historically, `CONFIG_ARCH_` was used for the bonafide architecture,
   e.g. SA1100, as well as implementations of the architecture,
   e.g. Assabet.  It was decided to change the implementation macros
   to read `CONFIG_MACH_` for clarity.  Moreover, a retroactive fixup has
   not been made because it would complicate patching.

   Previous registrations may be found online.

     <http://www.arm.linux.org.uk/developer/machines/>

 Kernel entry (head.S)
 ---------------------
   The initial entry into the kernel is via head.S, which uses machine
   independent code.  The machine is selected by the value of 'r1' on
   entry, which must be kept unique.

   Due to the large number of machines which the ARM port of Linux provides
   for, we have a method to manage this which ensures that we don't end up
   duplicating large amounts of code.

   We group machine (or platform) support code into machine classes.  A
   class typically based around one or more system on a chip devices, and
   acts as a natural container around the actual implementations.  These
   classes are given directories - arch/arm/mach-<class> - which contain
   the source files and include/mach/ to support the machine class.

   For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
   devices, and contains the code to support the way the on-board and off-
   board devices are used, or the device is setup, and provides that
   machine specific "personality."

   For platforms that support device tree (DT), the machine selection is
   controlled at runtime by passing the device tree blob to the kernel.  At
   compile-time, support for the machine type must be selected.  This allows for
   a single multiplatform kernel build to be used for several machine types.

   For platforms that do not use device tree, this machine selection is
   controlled by the machine type ID, which acts both as a run-time and a
   compile-time code selection method.  You can register a new machine via the
   web site at:

     <http://www.arm.linux.org.uk/developer/machines/>

   Note: Please do not register a machine type for DT-only platforms.  If your
   platform is DT-only, you do not need a registered machine type.

 ---

 Russell King (15/03/2004)
	=======================
	ARM Linux 2.6 and upper
	=======================

	Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for
	updates.

	Compilation of kernel
	---------------------

	In order to compile ARM Linux, you will need a compiler capable of
	generating ARM ELF code with GNU extensions. GCC 3.3 is known to be
	a good compiler. Fortunately, you needn't guess. The kernel will report
	an error if your compiler is a recognized offender.

	To build ARM Linux natively, you shouldn't have to alter the ARCH = line
	in the top level Makefile. However, if you don't have the ARM Linux ELF
	tools installed as default, then you should change the CROSS_COMPILE
	line as detailed below.

	If you wish to cross-compile, then alter the following lines in the top
	level make file::

	ARCH = <whatever>

	with::

	ARCH = arm

	and::

	CROSS_COMPILE=

	to::

	CROSS_COMPILE=<your-path-to-your-compiler-without-gcc>

	eg.::

	CROSS_COMPILE=arm-linux-

	Do a 'make config', followed by 'make Image' to build the kernel
	(arch/arm/boot/Image). A compressed image can be built by doing a
	'make zImage' instead of 'make Image'.


	Bug reports etc
	---------------

	Please send patches to the patch system. For more information, see
	http://www.arm.linux.org.uk/developer/patches/info.php Always include some
	explanation as to what the patch does and why it is needed.

	Bug reports should be sent to [email protected],
	or submitted through the web form at
	http://www.arm.linux.org.uk/developer/

	When sending bug reports, please ensure that they contain all relevant
	information, eg. the kernel messages that were printed before/during
	the problem, what you were doing, etc.


	Include files
	-------------

	Several new include directories have been created under include/asm-arm,
	which are there to reduce the clutter in the top-level directory. These
	directories, and their purpose is listed below:

	============= ==========================================================
	`arch-*` machine/platform specific header files
	`hardware` driver-internal ARM specific data structures/definitions
	`mach` descriptions of generic ARM to specific machine interfaces
	`proc-*` processor dependent header files (currently only two
	categories)
	============= ==========================================================


	Machine/Platform support
	------------------------

	The ARM tree contains support for a lot of different machine types. To
	continue supporting these differences, it has become necessary to split
	machine-specific parts by directory. For this, the machine category is
	used to select which directories and files get included (we will use
	$(MACHINE) to refer to the category)

	To this end, we now have arch/arm/mach-$(MACHINE) directories which are
	designed to house the non-driver files for a particular machine (eg, PCI,
	memory management, architecture definitions etc). For all future
	machines, there should be a corresponding arch/arm/mach-$(MACHINE)/include/mach
	directory.


	Modules
	-------

	Although modularisation is supported (and required for the FP emulator),
	each module on an ARM2/ARM250/ARM3 machine when is loaded will take
	memory up to the next 32k boundary due to the size of the pages.
	Therefore, is modularisation on these machines really worth it?

	However, ARM6 and up machines allow modules to take multiples of 4k, and
	as such Acorn RiscPCs and other architectures using these processors can
	make good use of modularisation.


	ADFS Image files
	----------------

	You can access image files on your ADFS partitions by mounting the ADFS
	partition, and then using the loopback device driver. You must have
	losetup installed.

	Please note that the PCEmulator DOS partitions have a partition table at
	the start, and as such, you will have to give '-o offset' to losetup.


	Request to developers
	---------------------

	When writing device drivers which include a separate assembler file, please
	include it in with the C file, and not the arch/arm/lib directory. This
	allows the driver to be compiled as a loadable module without requiring
	half the code to be compiled into the kernel image.

	In general, try to avoid using assembler unless it is really necessary. It
	makes drivers far less easy to port to other hardware.


	ST506 hard drives
	-----------------

	The ST506 hard drive controllers seem to be working fine (if a little
	slowly). At the moment they will only work off the controllers on an
	A4x0's motherboard, but for it to work off a Podule just requires
	someone with a podule to add the addresses for the IRQ mask and the
	HDC base to the source.

	As of 31/3/96 it works with two drives (you should get the ADFS
	`*configure` harddrive set to 2). I've got an internal 20MB and a great
	big external 5.25" FH 64MB drive (who could ever want more :-) ).

	I've just got 240K/s off it (a dd with bs=128k); thats about half of what
	RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting
	last week :-)

	Known bug: Drive data errors can cause a hang; including cases where
	the controller has fixed the error using ECC. (Possibly ONLY
	in that case...hmm).


	1772 Floppy
	-----------
	This also seems to work OK, but hasn't been stressed much lately. It
	hasn't got any code for disc change detection in there at the moment which
	could be a bit of a problem! Suggestions on the correct way to do this
	are welcome.


	`CONFIG_MACH_` and `CONFIG_ARCH_`
	---------------------------------
	A change was made in 2003 to the macro names for new machines.
	Historically, `CONFIG_ARCH_` was used for the bonafide architecture,
	e.g. SA1100, as well as implementations of the architecture,
	e.g. Assabet. It was decided to change the implementation macros
	to read `CONFIG_MACH_` for clarity. Moreover, a retroactive fixup has
	not been made because it would complicate patching.

	Previous registrations may be found online.

	<http://www.arm.linux.org.uk/developer/machines/>

	Kernel entry (head.S)
	---------------------
	The initial entry into the kernel is via head.S, which uses machine
	independent code. The machine is selected by the value of 'r1' on
	entry, which must be kept unique.

	Due to the large number of machines which the ARM port of Linux provides
	for, we have a method to manage this which ensures that we don't end up
	duplicating large amounts of code.

	We group machine (or platform) support code into machine classes. A
	class typically based around one or more system on a chip devices, and
	acts as a natural container around the actual implementations. These
	classes are given directories - arch/arm/mach-<class> - which contain
	the source files and include/mach/ to support the machine class.

	For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
	devices, and contains the code to support the way the on-board and off-
	board devices are used, or the device is setup, and provides that
	machine specific "personality."

	For platforms that support device tree (DT), the machine selection is
	controlled at runtime by passing the device tree blob to the kernel. At
	compile-time, support for the machine type must be selected. This allows for
	a single multiplatform kernel build to be used for several machine types.

	For platforms that do not use device tree, this machine selection is
	controlled by the machine type ID, which acts both as a run-time and a
	compile-time code selection method. You can register a new machine via the
	web site at:

	<http://www.arm.linux.org.uk/developer/machines/>

	Note: Please do not register a machine type for DT-only platforms. If your
	platform is DT-only, you do not need a registered machine type.

	---

	Russell King (15/03/2004)