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 120const char *get_system_type(void) 121{ 122 return "FooTech Vaporboard"; 123} 124 125int __init platform_setup(void) 126{ 127 /* 128 * If our hardware actually existed, we would do real 129 * setup here. Though it's also sane to leave this empty 130 * if there's no real init work that has to be done for 131 * this board. 132 */ 133 134 /* Start-up imaginary PCI ... */ 135 136 /* And whatever else ... */ 137 138 return 0; 139} 140 141Our new imaginary board will also have to tie into the machvec in order for it 142to be of any use. 143 144machvec functions fall into a number of categories: 145 146 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc). 147 - I/O mapping functions (ioport_map, ioport_unmap, etc). 148 - a 'heartbeat' function. 149 - PCI and IRQ initialization routines. 150 - Consistent allocators (for boards that need special allocators, 151 particularly for allocating out of some board-specific SRAM for DMA 152 handles). 153 154There are machvec functions added and removed over time, so always be sure to 155consult include/asm-sh/machvec.h for the current state of the machvec. 156 157The kernel will automatically wrap in generic routines for undefined function 158pointers in the machvec at boot time, as machvec functions are referenced 159unconditionally throughout most of the tree. Some boards have incredibly 160sparse machvecs (such as the dreamcast and sh03), whereas others must define 161virtually everything (rts7751r2d). 162 163Adding a new machine is relatively trivial (using vapor as an example): 164 165If the board-specific definitions are quite minimalistic, as is the case for 166the vast majority of boards, simply having a single board-specific header is 167sufficient. 168 169 - add a new file include/asm-sh/vapor.h which contains prototypes for 170 any machine specific IO functions prefixed with the machine name, for 171 example vapor_inb. These will be needed when filling out the machine 172 vector. 173 174 Note that these prototypes are generated automatically by setting 175 __IO_PREFIX to something sensible. A typical example would be: 176 177 #define __IO_PREFIX vapor 178 #include <asm/io_generic.h> 179 180 somewhere in the board-specific header. Any boards being ported that still 181 have a legacy io.h should remove it entirely and switch to the new model. 182 183 - Add machine vector definitions to the board's setup.c. At a bare minimum, 184 this must be defined as something like: 185 186 struct sh_machine_vector mv_vapor __initmv = { 187 .mv_name = "vapor", 188 }; 189 ALIAS_MV(vapor) 190 191 - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of 192 the machine specific io functions (if there are enough to warrant it). 193 1943. Hooking into the Build System 195================================ 196 197Now that we have the corresponding directories setup, and all of the 198board-specific code is in place, it's time to look at how to get the 199whole mess to fit into the build system. 200 201Large portions of the build system are now entirely dynamic, and merely 202require the proper entry here and there in order to get things done. 203 204The first thing to do is to add an entry to arch/sh/Kconfig, under the 205"System type" menu: 206 207config SH_VAPOR 208 bool "Vapor" 209 help 210 select Vapor if configuring for a FooTech Vaporboard. 211 212next, this has to be added into arch/sh/Makefile. All boards require a 213machdir-y entry in order to be built. This entry needs to be the name of 214the board directory as it appears in arch/sh/boards, even if it is in a 215sub-directory (in which case, all parent directories below arch/sh/boards/ 216need to be listed). For our new board, this entry can look like: 217 218machdir-$(CONFIG_SH_VAPOR) += vapor 219 220provided that we've placed everything in the arch/sh/boards/vapor/ directory. 221 222Next, the build system assumes that your include/asm-sh directory will also 223be named the same. If this is not the case (as is the case with multiple 224boards belonging to a common family), then the directory name needs to be 225implicitly appended to incdir-y. The existing code manages this for the 226Solution Engine and hp6xx boards, so see these for an example. 227 228Once that is taken care of, it's time to add an entry for the mach type. 229This is done by adding an entry to the end of the arch/sh/tools/mach-types 230list. The method for doing this is self explanatory, and so we won't waste 231space restating it here. After this is done, you will be able to use 232implicit checks for your board if you need this somewhere throughout the 233common code, such as: 234 235 /* Make sure we're on the FooTech Vaporboard */ 236 if (!mach_is_vapor()) 237 return -ENODEV; 238 239also note that the mach_is_boardname() check will be implicitly forced to 240lowercase, regardless of the fact that the mach-types entries are all 241uppercase. You can read the script if you really care, but it's pretty ugly, 242so you probably don't want to do that. 243 244Now all that's left to do is providing a defconfig for your new board. This 245way, other people who end up with this board can simply use this config 246for reference instead of trying to guess what settings are supposed to be 247used on it. 248 249Also, as soon as you have copied over a sample .config for your new board 250(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a 251build target, and it will be implicitly listed as such in the help text. 252 253Looking at the 'make help' output, you should now see something like: 254 255Architecture specific targets (sh): 256 zImage - Compressed kernel image (arch/sh/boot/zImage) 257 adx_defconfig - Build for adx 258 cqreek_defconfig - Build for cqreek 259 dreamcast_defconfig - Build for dreamcast 260... 261 vapor_defconfig - Build for vapor 262 263which then allows you to do: 264 265$ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux 266 267which will in turn copy the defconfig for this board, run it through 268oldconfig (prompting you for any new options since the time of creation), 269and start you on your way to having a functional kernel for your new 270board. 271