Linux Portingfor new ARM platform

Champ Yenhttp://champyen.blogspot.comchamp.yen@gmail.com

OutLine

GNU Toolchain

Linux Kernel Prerequisites and Assumptions

Images

Boot Sequence

Kernel Configuration & Compilation

Kernel Porting

Device Drivers

Boot Options

initramfs vs initrd

References

GNU Toolchains

CodeSourcery gnu toolchainhttp://www.codesourcery.com/sgpp/lite/arm/download.html

Buildroothttp://buildroot.uclibc.org/

Scratchboxhttp://www.scratchbox.org/

OpenEmbeddedhttp://wiki.openembedded.net/index.php/Main_Page

Ptxdisthttp://www.pengutronix.de/software/ptxdist/index_en.html

GNU Toolchains - buildroot

linux kernel like configuration interface

ncurse UI, .config file uClibc generate linux 2.6 compatible small footprint

applications for most platform remember to enable software float output: toolchain/uClibc/busybox/rootfs

Linux Kernel Prerequisites and Assumptions

DRAM is initialized Hardware-related initialization tasks are done MMU/Cache is disabled specific values should be saved in registers

r1: Machine ID, r2: pointer of ATAG list (optional)

Images and intermediate files

vmlinuz(ELF object)

kernel proper

objcopyimage(binary object)

stripped image binary kernel

gzip piggy.gz

compressedbinary kernel

asm

piggy.o

misc.o

head.o

bootablekernel image

(zImage)

Boot Sequence

arch/arm/boot/compressed/

head.S

bootstrap loader(uncompress)

start

arch/arm/kernel/head.S

start

ARM-specifickernel code

init/main.c

start_kernel

kernel code

detail boot sequence is listed in [9]

Kernel Porting – Kernel Memory Map

CPU vector page/copy_user_page(),clear_user_page()

DMA memory mapping

free for platform use

vmalloc()/ioremap() space

kernel direct-mapped RAM region

kernel module space

user space mapping

CPU vector page/null pointer trap0x0000_0000

0xFF00_0000

TASK_SIZE

PAGE_OFFSET

VMALLOC_START

VMALLOC_END

0x0000_1000

0xFFFF_0000

0xFFFF_FFFF

Kernel Porting – Directories

mm/memory-handling related code

boot/bootstrap loader code

kernel/ARM architecture dependent code

mach-XXXXXX/specific machine dependent code

configs/each machine’s default kernel configurations

Kernel Porting – new machine items

refer to other machine to create or modify items(ex: foo, fxx) register the new machine

arch/arm/tools/mach-types

Create machine folderarch/arm/mach-fxx

arch/arm/mach-fxx/include/mach

Modify or Create Kconfig & Makefilearch/arm/Kconfig (usually add config ARCH_FXX for architecture)

arch/arm/Makefile

arch/arm/mm/Kconfig

arch/arm/mach-fxx/Kconfig (config MACH_FOO for machine)

arch/arm/mach-fxx/Makefile

arch/arm/mach-fxx/Makefile.boot (set zreladdr-y for image location)

Kernel Porting – new machine itemsregister the new machine

Add an entry in arch/arm/tools/mach-types

ex: foo MACH_FOO FOO 65535 For official registration, should register here, also.

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

Kernel Porting – new machine itemscreate machine folders

arm/arch/mach-fxx

for machine dependent source code arm/arm/mach-fxx/include/mach

for machine dependent headers/assembly

debug-macro.S: adduart, senduart, busyuart, waituartdma.hentry-macro.S: macro get_irqnr_and_basehardware.hio.hirqs.h: NR_IRQSmemory.h: PHYS_OFFSET

system.h: arch_idle(), arch_reset()timex.h: CLOCK_TICK_RATEuncompress.h: putc()vmalloc.h: VMALLOC_END

Kernel Porting – new machine itemsmodify or create Kconfig & Makefile

arch/arm/Kconfigconfig ARCH_FXX

bool “FXX family processors“

help

This enables support for systems based on the fxx processors.

………

source "arch/arm/mach-fxx/Kconfig"

arch/arm/Makefile machine-$(CONFIG_ARCH_FXX) := fxx

arch/arm/mm/Kconfig (ex: ARM926-based)config CPU_ARM926T

bool "Support ARM926T processor"

depends on ARCH_INTEGRATOR || ARCH_VERSATILE_PB || \

… || ARCH_FXX

default y if ARCH_VERSATILE_PB || ARCH_VERSATILE_AB || \

… || ARCH_FXX

Kernel Porting – new machine itemsmodify or create Kconfig & Makefile

arch/arm/mach-fxx/Kconfigmenu "FXX platform type“

depends on ARCH_FXX

config MACH_FOO

bool "Support FOO platform"

default y

help

Include support for the FOO platform.

endmenu

arch/arm/mach-fxx/Makefile# Common support (must be linked before board specific support)

obj-y :=

# Specific board support

obj-$(CONFIG_MACH_FOO) += core.o

arch/arm/mach-fxx/Makefile.bootzreladdr-y := 0x01008000

architecture depend code

machine depend code

Kernel Porting – description structure

MACHINE_START(FOO, "FOO processor") /* Maintainer: Champ Yen */ .map_io = foo_map_io, .init_irq = foo_init_irq, .init_machine = foo_init, .timer = &foo_timer, /* for ATAG list is optional */ .boot_params = 0x01000100,MACHINE_END

Kernel Porting – Initialization code

I/O Memory Mapping Table IRQ Timer

struct sys_timer

Initial order: .map_io .initrq .timer .init_machine

Kernel Porting – I/O Memory Map

static struct map_desc foo_io_desc[] __initdata =

{

{

/* address after mapping */

.virtual = IO_ADDRESS(CPU_DEV_PHY_BASE),

/* page index of physical address */

.pfn = __phys_to_pfn(CPU_DEV_PHY_BASE),

.length = CPU_DEV_IO_LEN, /* address mapping range */

.type = MT_DEVICE /* I/O type */

},

……

};

….

static void __init foo_map_io(void)

{

iotable_init(foo_io_desc, ARRAY_SIZE(foo_io_desc));

}

Kernel Porting – IRQ

arch/arm/mach-fxx/include/mach/entry-macro.Sget_irqnr_and_base: after calling irqnr: irq number, not equal condition should be set.

arch/arm/mach-fxx/include/mach/irqs.hNR_IRQS (number of irq types) should be defined

struct irq_chip, irqactionset_irq_chip(), set_irq_flags(), set_irq_handler(), setup_irq()

static struct irq_chip foo_irq_chip = { .ack = foo_int_ack, .mask = foo_int_mask, .unmask = foo_int_unmask,};

………for(i = o; i < NR_IRQS; i++){

set_irq_handler(i, handle_level_irq);set_irq_chip(i, &foo_irq_chip);set_irq_flags(i, IRQF_VALID);

}………

Kernel Porting - Timer

struct sys_timer foo_timer = {

.init = foo_timer_init,

.offset = foo_gettimeoffset,

};

Kernel Porting – DMA memory (optional)

Influence to dma_alloc_coherent() usage In arch/arm/mach-fxx/include/mach/dma.h

MAX_DMA_ADDRESS In arch/arm/mach-fxx/include/mach/memory.h

CONSISTENT_DMA_SIZE ISA_DMA_THRESHOLD

Boot Options – static string

Boot options -> Default kernel command stringex: mem=8M@0x01000000 initrd=0x01180000,145762

Boot Options – ATAG lists

ATAG provides dynamic boot option passing There are two way to pass pointer of ATAG lists

r2 value passed by bootloader, .boot_params in machine descriptor

refer to arch/arm/include/asm/setup.h

……

ATAG_CORE

ATAG_NONE

struct tag_header { __u32 size; __u32 tag;};

struct tag { struct tag_header hdr; union { struct tag_core core; struct tag_mem32 mem;

… } u;};

Device Drivers

platform_device_register(), platform_driver_register()for some on-chip devices(ex: clock/power control)

UART subsystem in driver/serialfor startup message, console ,and shell

Framebuffer subsystem in driver/video

initramfs vs initrd

initrd initramfs

image ext2 image + gzip cpio + gzip

implementation block device tmpfs

first execution /linuxrc /init

mount rootfs pivot_root switch_root

initrd requires ext2 and block devices support. It adds 150KB+to kernel size.

initramfs

create an initramfs image by command: find . | cpio -o -H newc | gzip > ../initramfs.cpio.gz

take care of the distance between image and kernel, otherwise image will be overwritten by kernel.

/init

ex:#!/bin/busybox sh

#/bin/busybox --install

mount -t proc proc /proc

exec /bin/busybox sh

initramfs

Debug

decompression: putc() definiition in include/mach/uncompress.h

kernel debugging features in kernel hacking of kernel options (and CONFIG_DEBUG_LL option for low level debugging)

early debug: printascii/printhex(2,4,8) make use of uart macros in include/mach/debug-macro.S

printk()

CONNFIG_KGDB

References

Embedded Linux Primer, Christopher Hallinan, Prentice Hall Building Embedded Linux Systems 2/e, Karim Yaghmour, Oreilly linux-2.6.2x-xx/Documentation/arm http://heaven.branda.to/~thinker/GinGin_CGI.py/get_afile/166/porting_to_arm.pdf http://www.glomationinc.com/PortingLinuxKernel.pdf http://www.ens-lyon.fr/LIP/Pub/Rapports/RR/RR2006/RR2006-08.pdf http://glt08.linuxtage.at/slides/glt08-kvas_linuxonarm.pdf http://www.linux-arm.org/LinuxKernel/LinuxNewPlatformPort http://gicl.cs.drexel.edu/people/sevy/linux/ARM_Linux_boot_sequence.html http://www.simtec.co.uk/products/SWLINUX/files/booting_article.html http://www.ibm.com/developerworks/linux/library/l-initrd.html http://blog.linux.org.tw/~jserv/archives/001954.html

Q & A