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Linux Porting
 

Linux Porting

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linux porting to a new arm-based platform

linux porting to a new arm-based platform

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    Linux Porting Linux Porting Presentation Transcript

    • Linux Porting for new ARM platform Champ Yen http://champyen.blogspot.com champ.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 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 piggy.o image vmlinuz objcopy (binary gzip piggy.gz asm (ELF object) object) misc.o compressed head.o stripped image binary kernel binary kernel bootable kernel image kernel proper (zImage)
    • Boot Sequence start arch/arm/boot/ start compressed/ head.S start_kernel arch/arm/kernel/ head.S bootstrap loader init/main.c (uncompress) ARM-specific kernel code kernel code detail boot sequence is listed in [9]
    • Kernel Porting – Kernel Memory Map 0xFFFF_FFFF CPU vector page/copy_user_page(),clear_user_page() 0xFFFF_0000 DMA memory mapping 0xFF00_0000 free for platform use VMALLOC_END vmalloc()/ioremap() space VMALLOC_START kernel direct-mapped RAM region PAGE_OFFSET kernel module space TASK_SIZE user space mapping 0x0000_1000 CPU vector page/null pointer trap 0x0000_0000
    • 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 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  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 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 system.h: arch_idle(), arch_reset() io.h timex.h: CLOCK_TICK_RATE irqs.h: NR_IRQS uncompress.h: putc() memory.h: PHYS_OFFSET vmalloc.h: VMALLOC_END
    • Kernel Porting – new machine items modify or create Kconfig & Makefile  arch/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"  arch/arm/Makefile machine-$(CONFIG_ARCH_FXX) := fxx  arch/arm/mm/Kconfig (ex: ARM926-based) config CPU_ARM926T bool "Support ARM926T processor" depends on ARCH_INTEGRATOR || ARCH_VERSATILE_PB || … || ARCH_FXX default y if ARCH_VERSATILE_PB || ARCH_VERSATILE_AB || … || ARCH_FXX
    • Kernel Porting – new machine items modify or create Kconfig & Makefile  arch/arm/mach-fxx/Kconfig menu "FXX platform type“ depends on ARCH_FXX config MACH_FOO bool "Support FOO platform" default y help Include support for the FOO platform. endmenu  arch/arm/mach-fxx/Makefile # Common support (must be linked before board specific support) obj-y := architecture depend code # Specific board support obj-$(CONFIG_MACH_FOO) += core.o machine depend code  arch/arm/mach-fxx/Makefile.boot zreladdr-y := 0x01008000
    • 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 = { for(i = o; i < NR_IRQS; i++){ .ack = foo_int_ack, set_irq_handler(i, handle_level_irq); .mask = foo_int_mask, set_irq_chip(i, &foo_irq_chip); .unmask = foo_int_unmask, 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 struct tag_header { __u32 size; ATAG_CORE __u32 tag; }; …… struct tag { struct tag_header hdr; union { struct tag_core core; struct tag_mem32 mem; … } u; ATAG_NONE };
    • 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 /proc exec /bin/busybox sh
    • 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