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When U-Boot started using SPDX tags we were among the early adopters and there weren't a lot of other examples to borrow from. So we picked the area of the file that usually had a full license text and replaced it with an appropriate SPDX-License-Identifier: entry. Since then, the Linux Kernel has adopted SPDX tags and they place it as the very first line in a file (except where shebangs are used, then it's second line) and with slightly different comment styles than us. In part due to community overlap, in part due to better tag visibility and in part for other minor reasons, switch over to that style. This commit changes all instances where we have a single declared license in the tag as both the before and after are identical in tag contents. There's also a few places where I found we did not have a tag and have introduced one. Signed-off-by: Tom Rini <trini@konsulko.com>
135 lines
5.5 KiB
Text
135 lines
5.5 KiB
Text
# SPDX-License-Identifier: GPL-2.0+
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#
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# (C) Copyright 2014 Google, Inc
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# Simon Glass <sjg@chromium.org>
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Background
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----------
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U-Boot traditionally had a board.c file for each architecture. This introduced
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quite a lot of duplication, with each architecture tending to do
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initialisation slightly differently. To address this, a new 'generic board
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init' feature was introduced in March 2013 (further motivation is
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provided in the cover letter below).
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All boards and architectures have moved to this as of mid 2016.
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What has changed?
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-----------------
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The main change is that the arch/<arch>/lib/board.c file is removed in
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favour of common/board_f.c (for pre-relocation init) and common/board_r.c
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(for post-relocation init).
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Related to this, the global_data and bd_t structures now have a core set of
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fields which are common to all architectures. Architecture-specific fields
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have been moved to separate structures.
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Further Background
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------------------
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The full text of the original generic board series is reproduced below.
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--8<-------------
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This series creates a generic board.c implementation which contains
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the essential functions of the major arch/xxx/lib/board.c files.
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What is the motivation for this change?
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1. There is a lot of repeated code in the board.c files. Any change to
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things like setting up the baud rate requires a change in 10 separate
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places.
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2. Since there are 10 separate files, adding a new feature which requires
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initialisation is painful since it must be independently added in 10
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places.
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3. As time goes by the architectures naturally diverge since there is limited
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pressure to compare features or even CONFIG options against similar things
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in other board.c files.
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4. New architectures must implement all the features all over again, and
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sometimes in subtle different ways. This places an unfair burden on getting
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a new architecture fully functional and running with U-Boot.
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5. While it is a bit of a tricky change, I believe it is worthwhile and
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achievable. There is no requirement that all code be common, only that
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the code that is common should be located in common/board.c rather than
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arch/xxx/lib/board.c.
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All the functions of board_init_f() and board_init_r() are broken into
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separate function calls so that they can easily be included or excluded
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for a particular architecture. It also makes it easier to adopt Graeme's
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initcall proposal when it is ready.
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http://lists.denx.de/pipermail/u-boot/2012-January/114499.html
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This series removes the dependency on generic relocation. So relocation
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happens as one big chunk and is still completely arch-specific. See the
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relocation series for a proposed solution to this for ARM:
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http://lists.denx.de/pipermail/u-boot/2011-December/112928.html
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or Graeme's recent x86 series v2:
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http://lists.denx.de/pipermail/u-boot/2012-January/114467.html
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Instead of moving over a whole architecture, this series takes the approach
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of simply enabling generic board support for an architecture. It is then up
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to each board to opt in by defining CONFIG_SYS_GENERIC_BOARD in the board
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config file. If this is not done, then the code will be generated as
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before. This allows both sets of code to co-exist until we are comfortable
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with the generic approach, and enough boards run.
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ARM is a relatively large board.c file and one which I can test, therefore
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I think it is a good target for this series. On the other hand, x86 is
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relatively small and simple, but different enough that it introduces a
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few issues to be solved. So I have chosen both ARM and x86 for this series.
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After a suggestion from Wolfgang I have added PPC also. This is the
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largest and most feature-full board, so hopefully we have all bases
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covered in this RFC.
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A generic global_data structure is also required. This might upset a few
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people. Here is my basic reasoning: most fields are the same, all
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architectures include and need it, most global_data.h files already have
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#ifdefs to select fields for a particular SOC, so it is hard to
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see why architecures are different in this area. We can perhaps add a
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way to put architecture-specific fields into a separate header file, but
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for now I have judged that to be counter-productive.
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Similarly we need a generic bd_info structure, since generic code will
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be accessing it. I have done this in the same way as global_data and the
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same comments apply.
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There was dicussion on the list about passing gd_t around as a parameter
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to pre-relocation init functions. I think this makes sense, but it can
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be done as a separate change, and this series does not require it.
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While this series needs to stand on its own (as with the link script
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cleanup series and the generic relocation series) the goal is the
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unification of the board init code. So I hope we can address issues with
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this in mind, rather than focusing too narrowly on particular ARM, x86 or
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PPC issues.
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I have run-tested ARM on Tegra Seaboard only. To try it out, define
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CONFIG_SYS_GENERIC_BOARD in your board file and rebuild. Most likely on
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x86 and PPC at least it will hang, but if you are lucky it will print
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something first :-)
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I have run this though MAKEALL with CONFIG_SYS_GENERIC_BOARD on for all
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ARM, PPC and x86 boards. There are a few failures due to errors in
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the board config, which I have sent patches for. The main issue is
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just the difference between __bss_end and __bss_end__.
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Note: the first group of commits are required for this series to build,
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but could be separated out if required. I have included them here for
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convenience.
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------------->8--
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Simon Glass, sjg@chromium.org
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March 2014
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Updated after final removal, May 2016
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