Linux Porting

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linux porting to a new arm-based platform

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Linux Porting

  1. 1. Linux Porting for new ARM platform Champ Yen http://champyen.blogspot.com champ.yen@gmail.com
  2. 2. OutLine GNU Toolchain Linux Kernel Prerequisites and Assumptions Images Boot Sequence Kernel Configuration & Compilation Kernel Porting Device Drivers Boot Options initramfs vs initrd References
  3. 3. 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
  4. 4. 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
  5. 5. 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)
  6. 6. 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)
  7. 7. 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]
  8. 8. 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
  9. 9. 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
  10. 10. 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)
  11. 11. 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/
  12. 12. 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
  13. 13. 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-$(CONFIG_ARCH_FXX) := fxx  arch/arm/mm/Kconfig (ex: ARM926-based) config CPU_ARM926T bool "Support ARM926T processor" depends on ARCH_INTEGRATOR || ARCH_VERSATILE_PB || … || ARCH_FXX default y if ARCH_VERSATILE_PB || ARCH_VERSATILE_AB || … || ARCH_FXX
  14. 14. Kernel Porting – new machine items modify or create Kconfig & Makefile  arch/arm/mach-fxx/Kconfig menu "FXX platform type“ depends on ARCH_FXX config MACH_FOO bool "Support FOO platform" default y help Include support for the FOO platform. endmenu  arch/arm/mach-fxx/Makefile # Common support (must be linked before board specific support) obj-y := architecture depend code # Specific board support obj-$(CONFIG_MACH_FOO) += core.o machine depend code  arch/arm/mach-fxx/Makefile.boot zreladdr-y := 0x01008000
  15. 15. 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
  16. 16. Kernel Porting – Initialization code  I/O Memory Mapping Table  IRQ  Timer struct sys_timer  Initial order: .map_io .initrq .timer .init_machine
  17. 17. 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)); }
  18. 18. 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); }; } ………
  19. 19. Kernel Porting - Timer struct sys_timer foo_timer = { .init = foo_timer_init, .offset = foo_gettimeoffset, };
  20. 20. 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
  21. 21. Boot Options – static string  Boot options -> Default kernel command string ex: mem=8M@0x01000000 initrd=0x01180000,145762
  22. 22. 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 };
  23. 23. 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
  24. 24. 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.
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. Q&A

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