從u-boot 移植 NDS32 談嵌入式系統開放原始碼開發的一些經驗

從 u-boot 移植 NDS32 談嵌入式系統開放原始碼開發的一些經驗 Macpaul Lin OSDC.TW 2011

這份投影片或許也對寫 Kernel, Driver, 以及 C 語言的人有幫助 ( 習慣良好的老鳥就不用聽這個了 )2011/03/25 Macpaul Lin - OSDC.TW 2011 2

其實是在講怎樣射打 patch2011/03/25 Macpaul Lin - OSDC.TW 2011 3

還有怎樣把爛 code 清乾淨2011/03/25 Macpaul Lin - OSDC.TW 2011 4

因為本來要射打的 patch 都一直被打（槍）2011/03/25 Macpaul Lin - OSDC.TW 2011 5

必要時還要幫老闆打槍打老闆的槍 (PATCH v1 started from 2010/08)2011/03/25 Macpaul Lin - OSDC.TW 2011 6

一切為的都是豬頭 code 的愛與和平呀2011/03/25 Macpaul Lin - OSDC.TW 2011 7

Who Am I?• Macpaul Lin – Interests and works: • Open Source • Networking • OpenWrt (2006 – 2010) • U-boot (2010 – 2011) – Contacts: • macpaul@gmail.com (macpaul@andestech.com) • http://www.plurk.com/macpaul • http://www.facebook.com/macpaul 2011/03/25 Macpaul Lin - OSDC.TW 2011 8

Outline• Introduction to u-boot project.• The software architecture of U-boot.• Code commit rules and work flow.• Suggestions and experiences sharing.2011/03/25 Macpaul Lin - OSDC.TW 2011 9

U-boot - History• http://en.wikipedia.org/wiki/Das_U-Boot • Das Unterseeboot – German for "the submarine."• GPL• Boot loader for embedded System • PPC, ARM, AVR32, MIPS, x86, 68k, Nios, and MicroBlaze. (and NDS32) • U-Boot originated in work done by Magnus Damm on a 8xx PowerPC bootloader called 8xxROM. • Wolfgang Denk moved the project to SourceForge.net. – http://www.denx.de/wiki/U-Boot/WebHome2011/03/25 Macpaul Lin - OSDC.TW 2011 10

U-boot – Boot Loader• http://en.wikipedia.org/wiki/Boot_loader#Bo ot_loader • Features – It prepars CPU and RAM to accesse the nonvolatile devices to load OS into ram. – It provides firmware upgrade and fail-safe functions. – It could run basic diagnostic and testing. – You can develop simple application on u-boot. • It also support non-OS frame buffer display (VFD).2011/03/25 Macpaul Lin - OSDC.TW 2011 11

u-boot – Why release code to u-boot is important ?• For customers, – Help on booting their devices. – Machine type ID is related to Linux Kernel bring up.• Release and Clean up is important. – Boss usually think clean up doesnt help on contribution to the company. – Dirty code and old code should be considered as garbage and debt. • No productivity to RD. – It made RD always maintaining old patches when new release on official project is coming.2011/03/25 Macpaul Lin - OSDC.TW 2011 12

U-boot – Development Model• Task Force – Gate Keepers (custodian) by git repository. • Functions, Architectures, and Vendors.• Schedule • Development happens in Release Cycles of 2 months. • The first 2 weeks are called Merge Window, which is followed by a Stabilization Period. • Patches with new code get only accepted while the Merge Window is open. • During the Stabilization Period, only patches that contain bug fixes get applied. • Release.2011/03/25 Macpaul Lin - OSDC.TW 2011 13

U-boot - Custodians• The Custodians take responsibility for some area (git repo) of the U-Boot code.• http://www.denx.de/wiki/U-Boot/Custodians • http://patchwork.ozlabs.org/project/uboot/list/2011/03/25 Macpaul Lin - OSDC.TW 2011 14

U-boot – Custodian git repo• The most stable and up-to-date main trunk will be under "master" branch.• The most new features and bug fix will be in "next" branch.2011/03/25 Macpaul Lin - OSDC.TW 2011 15

The System view of u-boot(boards.cfg)Target, ARCH, CPU, Board, Vendor, SoCa320evb arm arm920t ‐ faraday a320Sheevaplug arm arm926ejs ‐ Marvell kirkwoodadp‐ag101 nds32 n1213 adp‐ag101 AndesTech ag1012011/03/25 Macpaul Lin - OSDC.TW 2011 16

The software architecture of u-bootu‐boot ‐ api ‐ arch ‐ nds32 – cpu ‐ soc ‐ board ‐ include ‐ common ‐ lib ‐ drivers ‐ examples ‐ include ‐ lib ‐ net ‐ tools2011/03/25 Macpaul Lin - OSDC.TW 2011 17

Boot process of u-boot! Andesboot Startup Code (reset vector) (start.S)!! 1. bootstrap! 1.1 reset - start of Andesboot! 1.2 to superuser mode - as is when reset! 1.4 Do lowlevel_init! - (this will jump out to lowlevel_init.S in SoC)! - (lowlevel_init)! 1.3 Turn off watchdog timer! - (this will jump out to watchdog.S in SoC)! - (turnoff_watchdog)! 2. Do critical init when reboot (not from mem)! 3. Relocate andesboot to ram! 4. Setup stack! 5. Jump to second stage (start_andesboot)2011/03/25 Macpaul Lin - OSDC.TW 2011 18

Boot process of u-bootarch/nds32/start.S ‐>arch/nds32/cpu/n1213/ag101/lowlevel_init.S ‐> arch/nds32/start.S ‐>arch/nds32/cpu/n1213/ag101/watchdog.S ‐> arch/nds32/start.S ‐> start_andesboot() (arch/nds32/lib/board.c)2011/03/25 Macpaul Lin - OSDC.TW 2011 19

Boot process of u-boot(arch/nds32/lib/board.c)start_andesboot() ‐> init_sequence[] ‐> arch_cpu_init() pmu_init() board_init() interrupt_init() timer_init() env_init() init_baudrate() serial_init() ...2011/03/25 Macpaul Lin - OSDC.TW 2011 20

Boot process of u-boot(board/AndesTech/adp‐ag101.c)board_init()dram_init()board_eth_init()board_flash_get_legacy()2011/03/25 Macpaul Lin - OSDC.TW 2011 21

Board and System config in u-boot(include/configs/adp‐ag101.h)#define CONFIG_ADP_AG101#define CONFIG_SKIP_LOWLEVEL_INIT#define CONFIG_SYS_TEXT_BASE 0x03200000#define CONFIG_SYS_CLK_FREQ 48000000#define CONFIG_BAUDRATE 38400#define CONFIG_STACKSIZE (128 * 1024)#ifdef CONFIG_FTSDMC021#include <faraday/ftsdmc021.h>#define PHYS_SDRAM_0_SIZE 0x04000000 (64MB)2011/03/25 Macpaul Lin - OSDC.TW 2011 22

Code commit rules and work flow• U-boot Mailing list: – u-boot@lists.denx.de – http://lists.denx.de/mailman/listinfo/u-boot – Archives: http://lists.denx.de/pipermail/u-boot/ 2011/03/25 Macpaul Lin - OSDC.TW 2011 23

u-boot – commit rules• Patches with related features go together.• Patches must be ordered and bisected. – Headers comes before C files. – Conformed to make and build logic.• Patches must go with clear descriptions. – Subject (in category) – Descriptions – Signed-off• Revised patches must be labeled with versions and simple change log.• Custodians will test and apply the patches.2011/03/25 Macpaul Lin - OSDC.TW 2011 24

Patches with related features go together• Use git rebase -i HEAD~7 – git commit --amend – git rebase --continuends32/ag101/adp-ag101: add board adp-ag101 supportnds32: common bdinfo, bootm, image supportnds32: standalone supportnds32/lib: add generic funcs in NDS32 libnds32/ag101: cpu and init funcs of SoC ag101nds32/core N1213: NDS32 N12 core family N1213nds32: add header files support for nds322011/03/25 Macpaul Lin - OSDC.TW 2011 25

Split git commits• 我接手 u-boot 的時候整包 code 全部被綁在 2 個 patch (git commits) 裡面• patchutils (doesnt compatible with git) – filterdiff • Same single patch file into hunks. – splitdiff • Split out every single file-level patch.2011/03/25 Macpaul Lin - OSDC.TW 2011 26

Patches must go with clear descriptions.Author: Macpaul Lin <macpaul@andestech.com>AuthorDate: Mon Oct 25 14:03:51 2010 +0800Commit: macpaul <macpaul@andestech.com> subjectCommitDate: Sat Mar 26 00:54:17 2011 +0800 nds32: add NDS32 support into common header file description signed-off Add NDS32 support into common header file. git commit -s Signed‐off‐by: Macpaul Lin <macpaul@andestech.com> do not use:2011/03/25 bug number Macpaul Lin - OSDC.TW 2011 27

Revised patches must be labeled with versions and simple change logSigned‐off‐by: Macpaul Lin <macpaul@andestech.com>‐‐‐Changes for v1‐v4: ‐ Code cleanup and style formatting.Changes for v5‐v6: ‐ This patch also updated the following changes against the change after master tree (v2010.12‐rc1). ‐ fix upper case definitions in cache.h ‐ Support GD_FLG_ENV_READY and env_buf vars in nds32 global_data.h. ‐ Add readsb, writesb functions into io.h.2011/03/25 Macpaul Lin - OSDC.TW 2011 28http://www.kernel.org/pub/software/scm/git/docs/user‐manual.html#cleaning‐up‐history

Use git send-email to send the patch• Remembered add the mailing list and related developers into the cc. list.• git send-email goes plain text. – Do not add patch as an attachment. – Do not use mime-type in mail header. – Do not allow your company add "copyright" and "confidential" in the last section of your patch.2011/03/25 Macpaul Lin - OSDC.TW 2011 29

Coding style• Linux Coding style. – http://lxr.linux.no/#linux+v2.6.38/Documentati on/CodingStyle – linux/scripts/checkpatch.pl• U-boot Coding style. – http://www.denx.de/wiki/U-Boot/CodingStyle – http://lxr.linux.no/linux/Documentation/CodingS tyle2011/03/25 Macpaul Lin - OSDC.TW 2011 30

U-boot - Coding style• All variables, functions, marcos goes to full uppercase or lower case. – Do not use “int IE6mustDie;" declaration.• You must use model name to declare your device defines. • Device offset and defines 在 header file 宣告必須使用產品 " 型號 " ， • Ex: use FTSDMC021, FTSDMC020, – Do not use function description: “DRAM_CONTROLLER" • Ex: CONFIG_FTSDMC021_BANK_SIZE_1M – Do not use: SDRAM_BANK_SIZE_1M2011/03/25 Macpaul Lin - OSDC.TW 2011 31

U-boot - Coding style• Files in Makefile or in config.mk must be ordered. – A file begins with a must goes before then other begins with b. – Ex: +START = start.o +COBJS = interrupts.o cpu.o <--- 這樣會被打槍 – Please keep all such lists sorted. c < i.2011/03/25 Macpaul Lin - OSDC.TW 2011 32

U-boot - Coding style• Global code must never include any board specific header files. – This is fundeamentally flawed. – Wrong Ex: #include <board/AndesTech/include/porting.h> #include "../../../board/AndesTech/include/porting.h"• Declare register offsets by C structures, do not use #define. • If definitions of register offsets used by assembly code is necessary, use tool (make-asm-offset) to generate the asm. code.2011/03/25 Macpaul Lin - OSDC.TW 2011 33

U-boot - Coding style• Comment: – Ex: /* * reset handler */ or /* status register */ – Wrong Ex: /**************************** * reset handler *=========================== */ Macpaul Lin - OSDC.TW 20112011/03/25 34 // macpaul: bug fix: 2923: halt

Coding style• Coding style is related to version control system. – git (diff) is a mass of the stack of patches. – Reduce dependance between patches. – Reduce unnecessary and useless object, log, history in version control repository.• Do not follow the old days coding style. – Please keep your coding style rules updated. – Especially do not copy from “ARM” and “x86” code. 2011/03/25 Macpaul Lin - OSDC.TW 2011 35

Coding style• No Chinese in comment. if (sound) /* 開聲音 */ writeb(0x1, dev->mute);• Do not exceed 80 characters in a single line. – ~/.vimrc highlight OverLength ctermbg=red ctermfg=white guibg=#592929 match OverLength /%81v.+/• Do not use #if 0 and #if 1. – Use meaningful #define CONFIG_OSDC_TW_R12011/03/25 Macpaul Lin - OSDC.TW 2011 36

Coding style - misc – Do not use //... as comment. • please use /* … */ – Be careful on point statement • Ex: void *addr • Wrong Ex: – void * addr – Be careful on loop statement • Ex: – for (i = 0; i <= 5 ; i++) – Be careful on brace statement with correct space. • Ex: void test(void target, void case)2011/03/25 Macpaul Lin - OSDC.TW 2011 37

Coding style• You must maintain the commit year of your copyright/copyleft statement. – 不論 code 多老，只要 commit 沒有進 maintrunk ，都必須使用「真正」進 commit 的年份。 – Ex: # (C) Copyright 2006 Macpaul Lin, Andestech <macpaul@andestech.com> • Wolfgangs comment: – So no work has been done on this in the last 4 years? I guess you want to update your Copyright messages - all of them.2011/03/25 Macpaul Lin - OSDC.TW 2011 38

Coding style• The beginning of a functions is declaration. – Do not put comments at first. – Wrong Ex: void cleanup_before_linux(void) { /* this function is called just before we call linux */ int i; }2011/03/25 Macpaul Lin - OSDC.TW 2011 39

Coding style• Functional description goes before then function. – Ex: /* * reset handler */ void do_reset() {2011/03/25 Macpaul Lin - OSDC.TW 2011 40

Coding style• 每一行行尾不能有空白或者 t 字元結尾，所有的行尾都必須是非空白字元結尾。 – No trailing spaces. • "tt$", "t $", " t" – No spaces at the beginning. – Do not use mixed " t" to do indent.2011/03/25 Macpaul Lin - OSDC.TW 2011 41

Coding style – volatile • What is volatile? – http://en.wikipedia.org/wiki/Volatile_variable – http://en.wikipedia.org/wiki/Volatile_variable#Op timization_comparison_in_C • Do not use volatile in Linux, driver and boot loader. – http://lxr.linux.no/#linux+v2.6.38/Documentati on/volatile-considered-harmful.txt2011/03/25 Macpaul Lin - OSDC.TW 2011 42

Coding style – volatile• Like volatile, the kernel primitives which make concurrent access to data safe (spinlocks, mutexes, memory barriers, etc.) are designed to prevent unwanted optimization. – Proper spinlock. • Volatile variables without spinlock still cause problem. – Memory-mapped I/O register must be accessed by accessing functions with lock. – Proper code for busy Waiting. while (my_variable != what_i_want) cpu_relax();2011/03/25 Macpaul Lin - OSDC.TW 2011 43

Coding style – volatile• There are still a few rare situations where volatile makes sense in the kernel. • Accessor functions might use volatile on where direct I/O memory access does work. • Inline assembly code which changes memory, but which has no other visible side effects, risks being deleted by GCC. • The jiffies variable is special in that it can have a different value every time it is referenced, but it can be read without any special locking. • Pointers to data structures in coherent memory which might be modified by I/O devices can, sometimes, legitimately be volatile.2011/03/25 Macpaul Lin - OSDC.TW 2011 44

Coding style – volatile• Wolfgang: – Note: this also and especially applies to the "volatile" and "using I/O accessors instead of pointer acesses" issues. – [If not yet, you would probably soon run into issues when switching to GCC 4.5.x or even GCC 4.6.] • https://nongnu.org/software/gcc/gcc- 4.6/changes.html • A new switch -fstrict-volatile-bitfields has been added. Using it indicates that accesses to volatile bitfields should use a single access of the width of the fields type.2011/03/25 Macpaul Lin - OSDC.TW 2011 45

Coding Style – a testingprintf("n");printf("pc : [<%08lx>] sp: [<%08lx>]n" "ra : %08lx gp : %08lx fp : %08lxn", regs‐>PC, regs‐>SP, regs‐>RA, regs‐>GP, regs‐>FP);printf("D1H: %08lx D1L: %081x D0H: %08lx D0L: %08lxn", regs‐>D1HI, regs‐>D1LO, regs‐>D0HI, regs‐>D0LO);printf("r27: %08lx r26: %08lx r25: %081x r24: %08lxn", regs‐>R27, regs‐>R26, regs‐>R25, regs‐>R24);printf("r23: %08lx r22: %081x r21: %08lx r20: %08lxn", regs‐>R23, regs‐>R22, regs‐>R21, regs‐>R20);2011/03/25 Macpaul Lin - OSDC.TW 2011 46

Release early, release often.2011/03/25 Macpaul Lin - OSDC.TW 2011 47

Q & A. (Patch v7 for NDS32 porting is under cleanup.)2011/03/25 Macpaul Lin - OSDC.TW 2011 48

從u-boot 移植 NDS32 談嵌入式系統開放原始碼開發的一些經驗

by Macpaul Lin on Mar 26, 2011

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