Linux Porting

Linux Porting for new ARM platform Champ Yen http://champyen.blogspot.com [email_address]

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 toolchain

http://www.codesourcery.com/sgpp/lite/arm/download.html

Buildroot

http://buildroot.uclibc.org/

Scratchbox

http://www.scratchbox.org/

OpenEmbedded

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

Ptxdist

http://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 objcopy image (binary object) stripped image binary kernel gzip piggy.gz compressed binary kernel asm piggy.o misc.o head.o bootable kernel image (zImage)

Boot Sequence arch/arm/boot/ compressed/ head.S bootstrap loader (uncompress) start arch/arm/kernel/ head.S start ARM-specific kernel 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 trap 0x0000_0000 0xFF00_0000 TASK_SIZE PAGE_OFFSET VMALLOC_START VMALLOC_END 0x0000_1000 0xFFFF_0000 0xFFFF_FFFF

Kernel Porting – Directories

m m/

memory-handling related code

b oot/

bootstrap loader code

k ernel/

ARM architecture dependent code

m ach-XXXXXX/

specific machine dependent code

c onfigs/

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 folder

arch/arm/mach-fxx arch/arm/mach-fxx/include/mach

Modify or Create Kconfig & Makefile

arch/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 items register the new machine

A dd 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 items create 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, waituart dma.h entry-macro.S: macro get_irqnr_and_base hardware.h io.h irqs.h: NR_IRQS memory.h : PHYS_OFFSET system.h: arch_idle(), arch_reset() timex.h: CLOCK_TICK_RATE uncompress.h : putc() vmalloc.h: VMALLOC_END

Kernel Porting – new machine items modify or create Kconfig & Makefile

a rch/arm/Kconfig

config ARCH_FXX bool “FXX family processors“ help This enables support for systems based on the fxx processors. ……… source " arch/arm/mach-fxx/Kconfig "

a rch/arm/Makefile

machine-$(CONFIG_ ARCH_FXX ) := fxx

a rch/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 items modify or create Kconfig & Makefile

a rch/arm/mach-fxx/Kconfig

menu "AIT8XX platform type“ depends on ARCH_FXX config MACH_FOO bool "Support FOO platform" default y help Include support for the FOO platform. endmenu

a rch/arm/mach-fxx/Makefile

# Common support (must be linked before board specific support) obj-y := # Specific board support obj-$(CONFIG_ MACH_FOO ) += core.o

a rch/arm/mach-fxx/Makefile.boot

zreladdr-y := 0x01008000 machine depend code architecture 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.S

get_irqnr_and_base: after calling irqnr: irq number, not equal condition should be set.

arch/arm/mach-fxx/include/mach/irqs.h

NR_IRQS (number of irq types) should be defined

struct irq_chip, irqaction

set_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 string

ex: 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/serial

for 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 /pro c 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