linux/Documentation/sh/new-machine.txt
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   1
   2                Adding a new board to LinuxSH
   3               ================================
   4
   5               Paul Mundt <lethal@linux-sh.org>
   6
   7This document attempts to outline what steps are necessary to add support
   8for new boards to the LinuxSH port under the new 2.5 and 2.6 kernels. This
   9also attempts to outline some of the noticeable changes between the 2.4
  10and the 2.5/2.6 SH backend.
  11
  121. New Directory Structure
  13==========================
  14
  15The first thing to note is the new directory structure. Under 2.4, most
  16of the board-specific code (with the exception of stboards) ended up
  17in arch/sh/kernel/ directly, with board-specific headers ending up in
  18include/asm-sh/. For the new kernel, things are broken out by board type,
  19companion chip type, and CPU type. Looking at a tree view of this directory
  20hierarchy looks like the following:
  21
  22Board-specific code:
  23
  24.
  25|-- arch
  26|   `-- sh
  27|       `-- boards
  28|           |-- adx
  29|           |   `-- board-specific files
  30|           |-- bigsur
  31|           |   `-- board-specific files
  32|           |
  33|           ... more boards here ...
  34|
  35`-- include
  36    `-- asm-sh
  37        |-- adx
  38        |   `-- board-specific headers
  39        |-- bigsur
  40        |   `-- board-specific headers
  41        |
  42        .. more boards here ...
  43
  44Next, for companion chips:
  45.
  46`-- arch
  47    `-- sh
  48        `-- cchips
  49            `-- hd6446x
  50                `-- hd64461
  51                    `-- cchip-specific files
  52
  53... and so on. Headers for the companion chips are treated the same way as
  54board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the
  55hd64461-specific headers.
  56
  57Finally, CPU family support is also abstracted:
  58.
  59|-- arch
  60|   `-- sh
  61|       |-- kernel
  62|       |   `-- cpu
  63|       |       |-- sh2
  64|       |       |   `-- SH-2 generic files
  65|       |       |-- sh3
  66|       |       |   `-- SH-3 generic files
  67|       |       `-- sh4
  68|       |           `-- SH-4 generic files
  69|       `-- mm
  70|           `-- This is also broken out per CPU family, so each family can
  71|               have their own set of cache/tlb functions.
  72|
  73`-- include
  74    `-- asm-sh
  75        |-- cpu-sh2
  76        |   `-- SH-2 specific headers
  77        |-- cpu-sh3
  78        |   `-- SH-3 specific headers
  79        `-- cpu-sh4
  80            `-- SH-4 specific headers
  81
  82It should be noted that CPU subtypes are _not_ abstracted. Thus, these still
  83need to be dealt with by the CPU family specific code.
  84
  852. Adding a New Board
  86=====================
  87
  88The first thing to determine is whether the board you are adding will be
  89isolated, or whether it will be part of a family of boards that can mostly
  90share the same board-specific code with minor differences.
  91
  92In the first case, this is just a matter of making a directory for your
  93board in arch/sh/boards/ and adding rules to hook your board in with the
  94build system (more on this in the next section). However, for board families
  95it makes more sense to have a common top-level arch/sh/boards/ directory
  96and then populate that with sub-directories for each member of the family.
  97Both the Solution Engine and the hp6xx boards are an example of this.
  98
  99After you have setup your new arch/sh/boards/ directory, remember that you
 100should also add a directory in include/asm-sh for headers localized to this
 101board (if there are going to be more than one). In order to interoperate
 102seamlessly with the build system, it's best to have this directory the same
 103as the arch/sh/boards/ directory name, though if your board is again part of
 104a family, the build system has ways of dealing with this (via incdir-y
 105overloading), and you can feel free to name the directory after the family
 106member itself.
 107
 108There are a few things that each board is required to have, both in the
 109arch/sh/boards and the include/asm-sh/ hierarchy. In order to better
 110explain this, we use some examples for adding an imaginary board. For
 111setup code, we're required at the very least to provide definitions for
 112get_system_type() and platform_setup(). For our imaginary board, this
 113might look something like:
 114
 115/*
 116 * arch/sh/boards/vapor/setup.c - Setup code for imaginary board
 117 */
 118#include <linux/init.h>
 119#include <asm/rtc.h> /* for board_time_init() */
 120
 121const char *get_system_type(void)
 122{
 123        return "FooTech Vaporboard";
 124}
 125
 126int __init platform_setup(void)
 127{
 128        /*
 129         * If our hardware actually existed, we would do real
 130         * setup here. Though it's also sane to leave this empty
 131         * if there's no real init work that has to be done for
 132         * this board.
 133         */
 134
 135        /* 
 136         * Presume all FooTech boards have the same broken timer,
 137         * and also presume that we've defined foo_timer_init to
 138         * do something useful.
 139         */
 140        board_time_init = foo_timer_init;
 141
 142        /* Start-up imaginary PCI ... */
 143
 144        /* And whatever else ... */
 145
 146        return 0;
 147}
 148
 149Our new imaginary board will also have to tie into the machvec in order for it
 150to be of any use.
 151
 152machvec functions fall into a number of categories:
 153
 154 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc).
 155 - I/O mapping functions (ioport_map, ioport_unmap, etc).
 156 - a 'heartbeat' function.
 157 - PCI and IRQ initialization routines.
 158 - Consistent allocators (for boards that need special allocators,
 159   particularly for allocating out of some board-specific SRAM for DMA
 160   handles).
 161
 162There are machvec functions added and removed over time, so always be sure to
 163consult include/asm-sh/machvec.h for the current state of the machvec.
 164
 165The kernel will automatically wrap in generic routines for undefined function
 166pointers in the machvec at boot time, as machvec functions are referenced
 167unconditionally throughout most of the tree. Some boards have incredibly
 168sparse machvecs (such as the dreamcast and sh03), whereas others must define
 169virtually everything (rts7751r2d).
 170
 171Adding a new machine is relatively trivial (using vapor as an example):
 172
 173If the board-specific definitions are quite minimalistic, as is the case for
 174the vast majority of boards, simply having a single board-specific header is
 175sufficient.
 176
 177 - add a new file include/asm-sh/vapor.h which contains prototypes for
 178   any machine specific IO functions prefixed with the machine name, for
 179   example vapor_inb. These will be needed when filling out the machine
 180   vector.
 181
 182   Note that these prototypes are generated automatically by setting
 183   __IO_PREFIX to something sensible. A typical example would be:
 184
 185        #define __IO_PREFIX vapor
 186        #include <asm/io_generic.h>
 187
 188   somewhere in the board-specific header. Any boards being ported that still
 189   have a legacy io.h should remove it entirely and switch to the new model.
 190
 191 - Add machine vector definitions to the board's setup.c. At a bare minimum,
 192   this must be defined as something like:
 193
 194        struct sh_machine_vector mv_vapor __initmv = {
 195                .mv_name = "vapor",
 196        };
 197        ALIAS_MV(vapor)
 198
 199 - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of
 200   the machine specific io functions (if there are enough to warrant it).
 201
 2023. Hooking into the Build System
 203================================
 204
 205Now that we have the corresponding directories setup, and all of the
 206board-specific code is in place, it's time to look at how to get the
 207whole mess to fit into the build system.
 208
 209Large portions of the build system are now entirely dynamic, and merely
 210require the proper entry here and there in order to get things done.
 211
 212The first thing to do is to add an entry to arch/sh/Kconfig, under the
 213"System type" menu:
 214
 215config SH_VAPOR
 216        bool "Vapor"
 217        help
 218          select Vapor if configuring for a FooTech Vaporboard.
 219
 220next, this has to be added into arch/sh/Makefile. All boards require a
 221machdir-y entry in order to be built. This entry needs to be the name of
 222the board directory as it appears in arch/sh/boards, even if it is in a
 223sub-directory (in which case, all parent directories below arch/sh/boards/
 224need to be listed). For our new board, this entry can look like:
 225
 226machdir-$(CONFIG_SH_VAPOR)      += vapor
 227
 228provided that we've placed everything in the arch/sh/boards/vapor/ directory.
 229
 230Next, the build system assumes that your include/asm-sh directory will also
 231be named the same. If this is not the case (as is the case with multiple
 232boards belonging to a common family), then the directory name needs to be
 233implicitly appended to incdir-y. The existing code manages this for the
 234Solution Engine and hp6xx boards, so see these for an example.
 235
 236Once that is taken care of, it's time to add an entry for the mach type.
 237This is done by adding an entry to the end of the arch/sh/tools/mach-types
 238list. The method for doing this is self explanatory, and so we won't waste
 239space restating it here. After this is done, you will be able to use
 240implicit checks for your board if you need this somewhere throughout the
 241common code, such as:
 242
 243        /* Make sure we're on the FooTech Vaporboard */
 244        if (!mach_is_vapor())
 245                return -ENODEV;
 246
 247also note that the mach_is_boardname() check will be implicitly forced to
 248lowercase, regardless of the fact that the mach-types entries are all
 249uppercase. You can read the script if you really care, but it's pretty ugly,
 250so you probably don't want to do that.
 251
 252Now all that's left to do is providing a defconfig for your new board. This
 253way, other people who end up with this board can simply use this config
 254for reference instead of trying to guess what settings are supposed to be
 255used on it.
 256
 257Also, as soon as you have copied over a sample .config for your new board
 258(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a
 259build target, and it will be implicitly listed as such in the help text.
 260
 261Looking at the 'make help' output, you should now see something like:
 262
 263Architecture specific targets (sh):
 264  zImage                  - Compressed kernel image (arch/sh/boot/zImage)
 265  adx_defconfig           - Build for adx
 266  cqreek_defconfig        - Build for cqreek
 267  dreamcast_defconfig     - Build for dreamcast
 268...
 269  vapor_defconfig         - Build for vapor
 270
 271which then allows you to do:
 272
 273$ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux
 274
 275which will in turn copy the defconfig for this board, run it through
 276oldconfig (prompting you for any new options since the time of creation),
 277and start you on your way to having a functional kernel for your new
 278board.
 279
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