1.. SPDX-License-Identifier: GPL-2.0
   4Adding a new board to LinuxSH
   7               Paul Mundt <>
   9This document attempts to outline what steps are necessary to add support
  10for new boards to the LinuxSH port under the new 2.5 and 2.6 kernels. This
  11also attempts to outline some of the noticeable changes between the 2.4
  12and the 2.5/2.6 SH backend.
  141. New Directory Structure
  17The first thing to note is the new directory structure. Under 2.4, most
  18of the board-specific code (with the exception of stboards) ended up
  19in arch/sh/kernel/ directly, with board-specific headers ending up in
  20include/asm-sh/. For the new kernel, things are broken out by board type,
  21companion chip type, and CPU type. Looking at a tree view of this directory
  22hierarchy looks like the following:
  24Board-specific code::
  26    .
  27    |-- arch
  28    |   `-- sh
  29    |       `-- boards
  30    |           |-- adx
  31    |           |   `-- board-specific files
  32    |           |-- bigsur
  33    |           |   `-- board-specific files
  34    |           |
  35    |           ... more boards here ...
  36    |
  37    `-- include
  38        `-- asm-sh
  39            |-- adx
  40            |   `-- board-specific headers
  41            |-- bigsur
  42            |   `-- board-specific headers
  43            |
  44            .. more boards here ...
  46Next, for companion chips::
  48    .
  49    `-- arch
  50        `-- sh
  51            `-- cchips
  52                `-- hd6446x
  53                    `-- hd64461
  54                        `-- cchip-specific files
  56... and so on. Headers for the companion chips are treated the same way as
  57board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the
  58hd64461-specific headers.
  60Finally, CPU family support is also abstracted::
  62    .
  63    |-- arch
  64    |   `-- sh
  65    |       |-- kernel
  66    |       |   `-- cpu
  67    |       |       |-- sh2
  68    |       |       |   `-- SH-2 generic files
  69    |       |       |-- sh3
  70    |       |       |   `-- SH-3 generic files
  71    |       |       `-- sh4
  72    |       |           `-- SH-4 generic files
  73    |       `-- mm
  74    |           `-- This is also broken out per CPU family, so each family can
  75    |               have their own set of cache/tlb functions.
  76    |
  77    `-- include
  78        `-- asm-sh
  79            |-- cpu-sh2
  80            |   `-- SH-2 specific headers
  81            |-- cpu-sh3
  82            |   `-- SH-3 specific headers
  83            `-- cpu-sh4
  84                `-- SH-4 specific headers
  86It should be noted that CPU subtypes are _not_ abstracted. Thus, these still
  87need to be dealt with by the CPU family specific code.
  892. Adding a New Board
  92The first thing to determine is whether the board you are adding will be
  93isolated, or whether it will be part of a family of boards that can mostly
  94share the same board-specific code with minor differences.
  96In the first case, this is just a matter of making a directory for your
  97board in arch/sh/boards/ and adding rules to hook your board in with the
  98build system (more on this in the next section). However, for board families
  99it makes more sense to have a common top-level arch/sh/boards/ directory
 100and then populate that with sub-directories for each member of the family.
 101Both the Solution Engine and the hp6xx boards are an example of this.
 103After you have setup your new arch/sh/boards/ directory, remember that you
 104should also add a directory in include/asm-sh for headers localized to this
 105board (if there are going to be more than one). In order to interoperate
 106seamlessly with the build system, it's best to have this directory the same
 107as the arch/sh/boards/ directory name, though if your board is again part of
 108a family, the build system has ways of dealing with this (via incdir-y
 109overloading), and you can feel free to name the directory after the family
 110member itself.
 112There are a few things that each board is required to have, both in the
 113arch/sh/boards and the include/asm-sh/ hierarchy. In order to better
 114explain this, we use some examples for adding an imaginary board. For
 115setup code, we're required at the very least to provide definitions for
 116get_system_type() and platform_setup(). For our imaginary board, this
 117might look something like::
 119    /*
 120    * arch/sh/boards/vapor/setup.c - Setup code for imaginary board
 121    */
 122    #include <linux/init.h>
 124    const char *get_system_type(void)
 125    {
 126            return "FooTech Vaporboard";
 127    }
 129    int __init platform_setup(void)
 130    {
 131            /*
 132            * If our hardware actually existed, we would do real
 133            * setup here. Though it's also sane to leave this empty
 134            * if there's no real init work that has to be done for
 135            * this board.
 136            */
 138            /* Start-up imaginary PCI ... */
 140            /* And whatever else ... */
 142            return 0;
 143    }
 145Our new imaginary board will also have to tie into the machvec in order for it
 146to be of any use.
 148machvec functions fall into a number of categories:
 150 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc).
 151 - I/O mapping functions (ioport_map, ioport_unmap, etc).
 152 - a 'heartbeat' function.
 153 - PCI and IRQ initialization routines.
 154 - Consistent allocators (for boards that need special allocators,
 155   particularly for allocating out of some board-specific SRAM for DMA
 156   handles).
 158There are machvec functions added and removed over time, so always be sure to
 159consult include/asm-sh/machvec.h for the current state of the machvec.
 161The kernel will automatically wrap in generic routines for undefined function
 162pointers in the machvec at boot time, as machvec functions are referenced
 163unconditionally throughout most of the tree. Some boards have incredibly
 164sparse machvecs (such as the dreamcast and sh03), whereas others must define
 165virtually everything (rts7751r2d).
 167Adding a new machine is relatively trivial (using vapor as an example):
 169If the board-specific definitions are quite minimalistic, as is the case for
 170the vast majority of boards, simply having a single board-specific header is
 173 - add a new file include/asm-sh/vapor.h which contains prototypes for
 174   any machine specific IO functions prefixed with the machine name, for
 175   example vapor_inb. These will be needed when filling out the machine
 176   vector.
 178   Note that these prototypes are generated automatically by setting
 179   __IO_PREFIX to something sensible. A typical example would be::
 181        #define __IO_PREFIX vapor
 182        #include <asm/io_generic.h>
 184   somewhere in the board-specific header. Any boards being ported that still
 185   have a legacy io.h should remove it entirely and switch to the new model.
 187 - Add machine vector definitions to the board's setup.c. At a bare minimum,
 188   this must be defined as something like::
 190        struct sh_machine_vector mv_vapor __initmv = {
 191                .mv_name = "vapor",
 192        };
 193        ALIAS_MV(vapor)
 195 - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of
 196   the machine specific io functions (if there are enough to warrant it).
 1983. Hooking into the Build System
 201Now that we have the corresponding directories setup, and all of the
 202board-specific code is in place, it's time to look at how to get the
 203whole mess to fit into the build system.
 205Large portions of the build system are now entirely dynamic, and merely
 206require the proper entry here and there in order to get things done.
 208The first thing to do is to add an entry to arch/sh/Kconfig, under the
 209"System type" menu::
 211    config SH_VAPOR
 212            bool "Vapor"
 213            help
 214            select Vapor if configuring for a FooTech Vaporboard.
 216next, this has to be added into arch/sh/Makefile. All boards require a
 217machdir-y entry in order to be built. This entry needs to be the name of
 218the board directory as it appears in arch/sh/boards, even if it is in a
 219sub-directory (in which case, all parent directories below arch/sh/boards/
 220need to be listed). For our new board, this entry can look like::
 222    machdir-$(CONFIG_SH_VAPOR)  += vapor
 224provided that we've placed everything in the arch/sh/boards/vapor/ directory.
 226Next, the build system assumes that your include/asm-sh directory will also
 227be named the same. If this is not the case (as is the case with multiple
 228boards belonging to a common family), then the directory name needs to be
 229implicitly appended to incdir-y. The existing code manages this for the
 230Solution Engine and hp6xx boards, so see these for an example.
 232Once that is taken care of, it's time to add an entry for the mach type.
 233This is done by adding an entry to the end of the arch/sh/tools/mach-types
 234list. The method for doing this is self explanatory, and so we won't waste
 235space restating it here. After this is done, you will be able to use
 236implicit checks for your board if you need this somewhere throughout the
 237common code, such as::
 239        /* Make sure we're on the FooTech Vaporboard */
 240        if (!mach_is_vapor())
 241                return -ENODEV;
 243also note that the mach_is_boardname() check will be implicitly forced to
 244lowercase, regardless of the fact that the mach-types entries are all
 245uppercase. You can read the script if you really care, but it's pretty ugly,
 246so you probably don't want to do that.
 248Now all that's left to do is providing a defconfig for your new board. This
 249way, other people who end up with this board can simply use this config
 250for reference instead of trying to guess what settings are supposed to be
 251used on it.
 253Also, as soon as you have copied over a sample .config for your new board
 254(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a
 255build target, and it will be implicitly listed as such in the help text.
 257Looking at the 'make help' output, you should now see something like:
 259Architecture specific targets (sh):
 261  =======================   =============================================
 262  zImage                    Compressed kernel image (arch/sh/boot/zImage)
 263  adx_defconfig             Build for adx
 264  cqreek_defconfig          Build for cqreek
 265  dreamcast_defconfig       Build for dreamcast
 266  ...
 267  vapor_defconfig           Build for vapor
 268  =======================   =============================================
 270which then allows you to do::
 272    $ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux
 274which will in turn copy the defconfig for this board, run it through
 275oldconfig (prompting you for any new options since the time of creation),
 276and start you on your way to having a functional kernel for your new