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  • #
    # (C) Copyright 2014 Google, Inc
    # Simon Glass <sjg@chromium.org>
    #
    # SPDX-License-Identifier:	GPL-2.0+
    #
    
    DEPRECATION NOTICE FOR arch/<arch>/lib/board.c
    
    For board maintainers: Please submit patches for boards you maintain before
    July 2014, to make them use generic board.
    
    For architecture maintainers: Please submit patches to remove your
    architecture-specific board.c file before October 2014.
    
    
    Background
    ----------
    
    
    U-Boot has traditionally had a board.c file for each architecture. This has
    
    introduced quite a lot of duplication, with each architecture tending to do
    initialisation slightly differently. To address this, a new 'generic board
    init' feature was introduced a year ago in March 2013 (further motivation is
    provided in the cover letter below).
    
    
    What has changed?
    -----------------
    
    The main change is that the arch/<arch>/lib/board.c file is being removed in
    favour of common/board_f.c (for pre-relocation init) and common/board_r.c
    (for post-relocation init).
    
    Related to this, the global_data and bd_t structures now have a core set of
    fields which are common to all architectures. Architecture-specific fields
    have been moved to separate structures.
    
    
    Supported Arcthitectures
    ------------------------
    
    If you are unlucky then your architecture may not support generic board.
    
    The following architectures are supported now:
    
       powerpc
       sandbox
       x86
    
    If your architecture is not supported, you need to adjust your
    arch/<arch>/config.mk file to include:
    
       __HAVE_ARCH_GENERIC_BOARD := y
    
    and test it with a suitable board, as follows.
    
    
    Adding Support for your Board
    -----------------------------
    
    To enable generic board for your board, define CONFIG_SYS_GENERIC_BOARD in
    your board config header file.
    
    Test that U-Boot still functions correctly on your board, and fix any
    problems you find. Don't be surprised if there are no problems - generic
    board has had a reasonable amount of testing with common boards.
    
    
    DeadLine
    --------
    
    Please don't take this the wrong way - there is no intent to make your life
    miserable, and we have the greatest respect and admiration for U-Boot users.
    However, with any migration there has to be a period where the old way is
    deprecated and removed. Every patch to the deprecated code introduces a
    potential breakage in the new unused code. Therefore:
    
    Boards or architectures not converted over to general board by the
    end of 2014 may be forcibly changed over (potentially causing run-time
    breakage) or removed.
    
    
    
    Further Background
    ------------------
    
    The full text of the original generic board series is reproduced below.
    
    --8<-------------
    
    This series creates a generic board.c implementation which contains
    the essential functions of the major arch/xxx/lib/board.c files.
    
    What is the motivation for this change?
    
    1. There is a lot of repeated code in the board.c files. Any change to
    things like setting up the baud rate requires a change in 10 separate
    places.
    
    2. Since there are 10 separate files, adding a new feature which requires
    initialisation is painful since it must be independently added in 10
    places.
    
    3. As time goes by the architectures naturely diverge since there is limited
    pressure to compare features or even CONFIG options against simiilar things
    in other board.c files.
    
    4. New architectures must implement all the features all over again, and
    sometimes in subtley different ways. This places an unfair burden on getting
    a new architecture fully functional and running with U-Boot.
    
    5. While it is a bit of a tricky change, I believe it is worthwhile and
    achievable. There is no requirement that all code be common, only that
    the code that is common should be located in common/board.c rather than
    arch/xxx/lib/board.c.
    
    All the functions of board_init_f() and board_init_r() are broken into
    separate function calls so that they can easily be included or excluded
    for a particular architecture. It also makes it easier to adopt Graeme's
    initcall proposal when it is ready.
    
    http://lists.denx.de/pipermail/u-boot/2012-January/114499.html
    
    This series removes the dependency on generic relocation. So relocation
    happens as one big chunk and is still completely arch-specific. See the
    relocation series for a proposed solution to this for ARM:
    
    http://lists.denx.de/pipermail/u-boot/2011-December/112928.html
    
    or Graeme's recent x86 series v2:
    
    http://lists.denx.de/pipermail/u-boot/2012-January/114467.html
    
    Instead of moving over a whole architecture, this series takes the approach
    of simply enabling generic board support for an architecture. It is then up
    to each board to opt in by defining CONFIG_SYS_GENERIC_BOARD in the board
    config file. If this is not done, then the code will be generated as
    before. This allows both sets of code to co-exist until we are comfortable
    with the generic approach, and enough boards run.
    
    ARM is a relatively large board.c file and one which I can test, therefore
    I think it is a good target for this series. On the other hand, x86 is
    relatively small and simple, but different enough that it introduces a
    few issues to be solved. So I have chosen both ARM and x86 for this series.
    After a suggestion from Wolfgang I have added PPC also. This is the
    largest and most feature-full board, so hopefully we have all bases
    covered in this RFC.
    
    A generic global_data structure is also required. This might upset a few
    people. Here is my basic reasoning: most fields are the same, all
    architectures include and need it, most global_data.h files already have
    #ifdefs to select fields for a particular SOC, so it is hard to
    see why architecures are different in this area. We can perhaps add a
    way to put architecture-specific fields into a separate header file, but
    for now I have judged that to be counter-productive.
    
    Similarly we need a generic bd_info structure, since generic code will
    be accessing it. I have done this in the same way as global_data and the
    same comments apply.
    
    There was dicussion on the list about passing gd_t around as a parameter
    to pre-relocation init functions. I think this makes sense, but it can
    be done as a separate change, and this series does not require it.
    
    While this series needs to stand on its own (as with the link script
    cleanup series and the generic relocation series) the goal is the
    unification of the board init code. So I hope we can address issues with
    this in mind, rather than focusing too narrowly on particular ARM, x86 or
    PPC issues.
    
    I have run-tested ARM on Tegra Seaboard only. To try it out, define
    CONFIG_SYS_GENERIC_BOARD in your board file and rebuild. Most likely on
    x86 and PPC at least it will hang, but if you are lucky it will print
    something first :-)
    
    I have run this though MAKEALL with CONFIG_SYS_GENERIC_BOARD on for all
    ARM, PPC and x86 boards. There are a few failures due to errors in
    the board config, which I have sent patches for. The main issue is
    just the difference between __bss_end and __bss_end__.
    
    Note: the first group of commits are required for this series to build,
    but could be separated out if required. I have included them here for
    convenience.
    
    ------------->8--
    
    Simon Glass, sjg@chromium.org
    March 2014