Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 EST.
1 2 Adding a new board to LinuxSH 3 ================================ 4 5 Paul Mundt <lethal[AT]linux-sh[DOT]org> 6 7 This document attempts to outline what steps are necessary to add support 8 for new boards to the LinuxSH port under the new 2.5 and 2.6 kernels. This 9 also attempts to outline some of the noticeable changes between the 2.4 10 and the 2.5/2.6 SH backend. 11 12 1. New Directory Structure 13 ========================== 14 15 The first thing to note is the new directory structure. Under 2.4, most 16 of the board-specific code (with the exception of stboards) ended up 17 in arch/sh/kernel/ directly, with board-specific headers ending up in 18 include/asm-sh/. For the new kernel, things are broken out by board type, 19 companion chip type, and CPU type. Looking at a tree view of this directory 20 hierarchy looks like the following: 21 22 Board-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 44 Next, for companion chips: 45 . 46 `-- arch 47 `-- sh 48 `-- cchips 49 `-- hd6446x 50 |-- hd64461 51 | `-- cchip-specific files 52 `-- hd64465 53 `-- cchip-specific files 54 55 ... and so on. Headers for the companion chips are treated the same way as 56 board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the 57 hd64461-specific headers. 58 59 Finally, CPU family support is also abstracted: 60 . 61 |-- arch 62 | `-- sh 63 | |-- kernel 64 | | `-- cpu 65 | | |-- sh2 66 | | | `-- SH-2 generic files 67 | | |-- sh3 68 | | | `-- SH-3 generic files 69 | | `-- sh4 70 | | `-- SH-4 generic files 71 | `-- mm 72 | `-- This is also broken out per CPU family, so each family can 73 | have their own set of cache/tlb functions. 74 | 75 `-- include 76 `-- asm-sh 77 |-- cpu-sh2 78 | `-- SH-2 specific headers 79 |-- cpu-sh3 80 | `-- SH-3 specific headers 81 `-- cpu-sh4 82 `-- SH-4 specific headers 83 84 It should be noted that CPU subtypes are _not_ abstracted. Thus, these still 85 need to be dealt with by the CPU family specific code. 86 87 2. Adding a New Board 88 ===================== 89 90 The first thing to determine is whether the board you are adding will be 91 isolated, or whether it will be part of a family of boards that can mostly 92 share the same board-specific code with minor differences. 93 94 In the first case, this is just a matter of making a directory for your 95 board in arch/sh/boards/ and adding rules to hook your board in with the 96 build system (more on this in the next section). However, for board families 97 it makes more sense to have a common top-level arch/sh/boards/ directory 98 and then populate that with sub-directories for each member of the family. 99 Both the Solution Engine and the hp6xx boards are an example of this. 100 101 After you have setup your new arch/sh/boards/ directory, remember that you 102 should also add a directory in include/asm-sh for headers localized to this 103 board (if there are going to be more than one). In order to interoperate 104 seamlessly with the build system, it's best to have this directory the same 105 as the arch/sh/boards/ directory name, though if your board is again part of 106 a family, the build system has ways of dealing with this (via incdir-y 107 overloading), and you can feel free to name the directory after the family 108 member itself. 109 110 There are a few things that each board is required to have, both in the 111 arch/sh/boards and the include/asm-sh/ hierarchy. In order to better 112 explain this, we use some examples for adding an imaginary board. For 113 setup code, we're required at the very least to provide definitions for 114 get_system_type() and platform_setup(). For our imaginary board, this 115 might look something like: 116 117 /* 118 * arch/sh/boards/vapor/setup.c - Setup code for imaginary board 119 */ 120 #include <linux/init.h> 121 #include <asm/rtc.h> /* for board_time_init() */ 122 123 const char *get_system_type(void) 124 { 125 return "FooTech Vaporboard"; 126 } 127 128 int __init platform_setup(void) 129 { 130 /* 131 * If our hardware actually existed, we would do real 132 * setup here. Though it's also sane to leave this empty 133 * if there's no real init work that has to be done for 134 * this board. 135 */ 136 137 /* 138 * Presume all FooTech boards have the same broken timer, 139 * and also presume that we've defined foo_timer_init to 140 * do something useful. 141 */ 142 board_time_init = foo_timer_init; 143 144 /* Start-up imaginary PCI ... */ 145 146 /* And whatever else ... */ 147 148 return 0; 149 } 150 151 Our new imaginary board will also have to tie into the machvec in order for it 152 to be of any use. 153 154 machvec functions fall into a number of categories: 155 156 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc). 157 - I/O mapping functions (ioport_map, ioport_unmap, etc). 158 - a 'heartbeat' function. 159 - PCI and IRQ initialization routines. 160 - Consistent allocators (for boards that need special allocators, 161 particularly for allocating out of some board-specific SRAM for DMA 162 handles). 163 164 There are machvec functions added and removed over time, so always be sure to 165 consult include/asm-sh/machvec.h for the current state of the machvec. 166 167 The kernel will automatically wrap in generic routines for undefined function 168 pointers in the machvec at boot time, as machvec functions are referenced 169 unconditionally throughout most of the tree. Some boards have incredibly 170 sparse machvecs (such as the dreamcast and sh03), whereas others must define 171 virtually everything (rts7751r2d). 172 173 Adding a new machine is relatively trivial (using vapor as an example): 174 175 If the board-specific definitions are quite minimalistic, as is the case for 176 the vast majority of boards, simply having a single board-specific header is 177 sufficient. 178 179 - add a new file include/asm-sh/vapor.h which contains prototypes for 180 any machine specific IO functions prefixed with the machine name, for 181 example vapor_inb. These will be needed when filling out the machine 182 vector. 183 184 Note that these prototypes are generated automatically by setting 185 __IO_PREFIX to something sensible. A typical example would be: 186 187 #define __IO_PREFIX vapor 188 #include <asm/io_generic.h> 189 190 somewhere in the board-specific header. Any boards being ported that still 191 have a legacy io.h should remove it entirely and switch to the new model. 192 193 - Add machine vector definitions to the board's setup.c. At a bare minimum, 194 this must be defined as something like: 195 196 struct sh_machine_vector mv_vapor __initmv = { 197 .mv_name = "vapor", 198 }; 199 ALIAS_MV(vapor) 200 201 - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of 202 the machine specific io functions (if there are enough to warrant it). 203 204 3. Hooking into the Build System 205 ================================ 206 207 Now that we have the corresponding directories setup, and all of the 208 board-specific code is in place, it's time to look at how to get the 209 whole mess to fit into the build system. 210 211 Large portions of the build system are now entirely dynamic, and merely 212 require the proper entry here and there in order to get things done. 213 214 The first thing to do is to add an entry to arch/sh/Kconfig, under the 215 "System type" menu: 216 217 config SH_VAPOR 218 bool "Vapor" 219 help 220 select Vapor if configuring for a FooTech Vaporboard. 221 222 next, this has to be added into arch/sh/Makefile. All boards require a 223 machdir-y entry in order to be built. This entry needs to be the name of 224 the board directory as it appears in arch/sh/boards, even if it is in a 225 sub-directory (in which case, all parent directories below arch/sh/boards/ 226 need to be listed). For our new board, this entry can look like: 227 228 machdir-$(CONFIG_SH_VAPOR) += vapor 229 230 provided that we've placed everything in the arch/sh/boards/vapor/ directory. 231 232 Next, the build system assumes that your include/asm-sh directory will also 233 be named the same. If this is not the case (as is the case with multiple 234 boards belonging to a common family), then the directory name needs to be 235 implicitly appended to incdir-y. The existing code manages this for the 236 Solution Engine and hp6xx boards, so see these for an example. 237 238 Once that is taken care of, it's time to add an entry for the mach type. 239 This is done by adding an entry to the end of the arch/sh/tools/mach-types 240 list. The method for doing this is self explanatory, and so we won't waste 241 space restating it here. After this is done, you will be able to use 242 implicit checks for your board if you need this somewhere throughout the 243 common code, such as: 244 245 /* Make sure we're on the FooTech Vaporboard */ 246 if (!mach_is_vapor()) 247 return -ENODEV; 248 249 also note that the mach_is_boardname() check will be implicitly forced to 250 lowercase, regardless of the fact that the mach-types entries are all 251 uppercase. You can read the script if you really care, but it's pretty ugly, 252 so you probably don't want to do that. 253 254 Now all that's left to do is providing a defconfig for your new board. This 255 way, other people who end up with this board can simply use this config 256 for reference instead of trying to guess what settings are supposed to be 257 used on it. 258 259 Also, as soon as you have copied over a sample .config for your new board 260 (assume arch/sh/configs/vapor_defconfig), you can also use this directly as a 261 build target, and it will be implicitly listed as such in the help text. 262 263 Looking at the 'make help' output, you should now see something like: 264 265 Architecture specific targets (sh): 266 zImage - Compressed kernel image (arch/sh/boot/zImage) 267 adx_defconfig - Build for adx 268 cqreek_defconfig - Build for cqreek 269 dreamcast_defconfig - Build for dreamcast 270 ... 271 vapor_defconfig - Build for vapor 272 273 which then allows you to do: 274 275 $ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux 276 277 which will in turn copy the defconfig for this board, run it through 278 oldconfig (prompting you for any new options since the time of creation), 279 and start you on your way to having a functional kernel for your new 280 board.