1 # SPDX-License-Identifier: GPL-2.0+ 2 # 3 # (C) Copyright 2014 Google, Inc 4 # Simon Glass <sjg (a] chromium.org> 5 6 Background 7 ---------- 8 9 U-Boot traditionally had a board.c file for each architecture. This introduced 10 quite a lot of duplication, with each architecture tending to do 11 initialisation slightly differently. To address this, a new 'generic board 12 init' feature was introduced in March 2013 (further motivation is 13 provided in the cover letter below). 14 15 All boards and architectures have moved to this as of mid 2016. 16 17 18 What has changed? 19 ----------------- 20 21 The main change is that the arch/<arch>/lib/board.c file is removed in 22 favour of common/board_f.c (for pre-relocation init) and common/board_r.c 23 (for post-relocation init). 24 25 Related to this, the global_data and bd_t structures now have a core set of 26 fields which are common to all architectures. Architecture-specific fields 27 have been moved to separate structures. 28 29 30 Further Background 31 ------------------ 32 33 The full text of the original generic board series is reproduced below. 34 35 --8<------------- 36 37 This series creates a generic board.c implementation which contains 38 the essential functions of the major arch/xxx/lib/board.c files. 39 40 What is the motivation for this change? 41 42 1. There is a lot of repeated code in the board.c files. Any change to 43 things like setting up the baud rate requires a change in 10 separate 44 places. 45 46 2. Since there are 10 separate files, adding a new feature which requires 47 initialisation is painful since it must be independently added in 10 48 places. 49 50 3. As time goes by the architectures naturally diverge since there is limited 51 pressure to compare features or even CONFIG options against similar things 52 in other board.c files. 53 54 4. New architectures must implement all the features all over again, and 55 sometimes in subtle different ways. This places an unfair burden on getting 56 a new architecture fully functional and running with U-Boot. 57 58 5. While it is a bit of a tricky change, I believe it is worthwhile and 59 achievable. There is no requirement that all code be common, only that 60 the code that is common should be located in common/board.c rather than 61 arch/xxx/lib/board.c. 62 63 All the functions of board_init_f() and board_init_r() are broken into 64 separate function calls so that they can easily be included or excluded 65 for a particular architecture. It also makes it easier to adopt Graeme's 66 initcall proposal when it is ready. 67 68 http://lists.denx.de/pipermail/u-boot/2012-January/114499.html 69 70 This series removes the dependency on generic relocation. So relocation 71 happens as one big chunk and is still completely arch-specific. See the 72 relocation series for a proposed solution to this for ARM: 73 74 http://lists.denx.de/pipermail/u-boot/2011-December/112928.html 75 76 or Graeme's recent x86 series v2: 77 78 http://lists.denx.de/pipermail/u-boot/2012-January/114467.html 79 80 Instead of moving over a whole architecture, this series takes the approach 81 of simply enabling generic board support for an architecture. It is then up 82 to each board to opt in by defining CONFIG_SYS_GENERIC_BOARD in the board 83 config file. If this is not done, then the code will be generated as 84 before. This allows both sets of code to co-exist until we are comfortable 85 with the generic approach, and enough boards run. 86 87 ARM is a relatively large board.c file and one which I can test, therefore 88 I think it is a good target for this series. On the other hand, x86 is 89 relatively small and simple, but different enough that it introduces a 90 few issues to be solved. So I have chosen both ARM and x86 for this series. 91 After a suggestion from Wolfgang I have added PPC also. This is the 92 largest and most feature-full board, so hopefully we have all bases 93 covered in this RFC. 94 95 A generic global_data structure is also required. This might upset a few 96 people. Here is my basic reasoning: most fields are the same, all 97 architectures include and need it, most global_data.h files already have 98 #ifdefs to select fields for a particular SOC, so it is hard to 99 see why architecures are different in this area. We can perhaps add a 100 way to put architecture-specific fields into a separate header file, but 101 for now I have judged that to be counter-productive. 102 103 Similarly we need a generic bd_info structure, since generic code will 104 be accessing it. I have done this in the same way as global_data and the 105 same comments apply. 106 107 There was dicussion on the list about passing gd_t around as a parameter 108 to pre-relocation init functions. I think this makes sense, but it can 109 be done as a separate change, and this series does not require it. 110 111 While this series needs to stand on its own (as with the link script 112 cleanup series and the generic relocation series) the goal is the 113 unification of the board init code. So I hope we can address issues with 114 this in mind, rather than focusing too narrowly on particular ARM, x86 or 115 PPC issues. 116 117 I have run-tested ARM on Tegra Seaboard only. To try it out, define 118 CONFIG_SYS_GENERIC_BOARD in your board file and rebuild. Most likely on 119 x86 and PPC at least it will hang, but if you are lucky it will print 120 something first :-) 121 122 I have run this though MAKEALL with CONFIG_SYS_GENERIC_BOARD on for all 123 ARM, PPC and x86 boards. There are a few failures due to errors in 124 the board config, which I have sent patches for. The main issue is 125 just the difference between __bss_end and __bss_end__. 126 127 Note: the first group of commits are required for this series to build, 128 but could be separated out if required. I have included them here for 129 convenience. 130 131 ------------->8-- 132 133 Simon Glass, sjg (a] chromium.org 134 March 2014 135 Updated after final removal, May 2016 136
