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193 lines
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Plaintext
193 lines
7.0 KiB
Plaintext
#
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# (C) Copyright 2014 Google, Inc
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# Simon Glass <sjg@chromium.org>
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#
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# SPDX-License-Identifier: GPL-2.0+
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#
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DEPRECATION NOTICE FOR arch/<arch>/lib/board.c
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For board maintainers: Please submit patches for boards you maintain before
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July 2014, to make them use generic board.
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For architecture maintainers: Please submit patches to remove your
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architecture-specific board.c file before October 2014.
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Background
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----------
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U-Boot has traditionally had a board.c file for each architecture. This has
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introduced 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 a year ago in March 2013 (further motivation is
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provided in the cover letter below).
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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 being 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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Supported Architectures
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------------------------
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If you are unlucky then your architecture may not support generic board.
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The following architectures are supported now:
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arc
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arm
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avr32
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blackfin
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m68k
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microblaze
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mips
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nios2
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powerpc
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sandbox
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x86
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If your architecture is not supported, you need to select
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HAVE_GENERIC_BOARD in arch/Kconfig
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and test it with a suitable board, as follows.
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Adding Support for your Board
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-----------------------------
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To enable generic board for your board, define CONFIG_SYS_GENERIC_BOARD in
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your board config header file.
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Test that U-Boot still functions correctly on your board, and fix any
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problems you find. Don't be surprised if there are no problems - generic
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board has had a reasonable amount of testing with common boards.
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DeadLine
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--------
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Please don't take this the wrong way - there is no intent to make your life
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miserable, and we have the greatest respect and admiration for U-Boot users.
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However, with any migration there has to be a period where the old way is
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deprecated and removed. Every patch to the deprecated code introduces a
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potential breakage in the new unused code. Therefore:
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Boards or architectures not converted over to general board by the
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end of 2014 may be forcibly changed over (potentially causing run-time
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breakage) or removed.
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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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