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1.. SPDX-License-Identifier: GPL-2.02 3=============================4Adding a new board to LinuxSH5=============================6 7 Paul Mundt <lethal@linux-sh.org>8 9This document attempts to outline what steps are necessary to add support10for new boards to the LinuxSH port under the new 2.5 and 2.6 kernels. This11also attempts to outline some of the noticeable changes between the 2.412and the 2.5/2.6 SH backend.13 141. New Directory Structure15==========================16 17The first thing to note is the new directory structure. Under 2.4, most18of the board-specific code (with the exception of stboards) ended up19in arch/sh/kernel/ directly, with board-specific headers ending up in20include/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 directory22hierarchy looks like the following:23 24Board-specific code::25 26 .27 |-- arch28 | `-- sh29 | `-- boards30 | |-- adx31 | | `-- board-specific files32 | |-- bigsur33 | | `-- board-specific files34 | |35 | ... more boards here ...36 |37 `-- include38 `-- asm-sh39 |-- adx40 | `-- board-specific headers41 |-- bigsur42 | `-- board-specific headers43 |44 .. more boards here ...45 46Next, for companion chips::47 48 .49 `-- arch50 `-- sh51 `-- cchips52 `-- hd6446x53 `-- hd6446154 `-- cchip-specific files55 56... and so on. Headers for the companion chips are treated the same way as57board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the58hd64461-specific headers.59 60Finally, CPU family support is also abstracted::61 62 .63 |-- arch64 | `-- sh65 | |-- kernel66 | | `-- cpu67 | | |-- sh268 | | | `-- SH-2 generic files69 | | |-- sh370 | | | `-- SH-3 generic files71 | | `-- sh472 | | `-- SH-4 generic files73 | `-- mm74 | `-- This is also broken out per CPU family, so each family can75 | have their own set of cache/tlb functions.76 |77 `-- include78 `-- asm-sh79 |-- cpu-sh280 | `-- SH-2 specific headers81 |-- cpu-sh382 | `-- SH-3 specific headers83 `-- cpu-sh484 `-- SH-4 specific headers85 86It should be noted that CPU subtypes are _not_ abstracted. Thus, these still87need to be dealt with by the CPU family specific code.88 892. Adding a New Board90=====================91 92The first thing to determine is whether the board you are adding will be93isolated, or whether it will be part of a family of boards that can mostly94share the same board-specific code with minor differences.95 96In the first case, this is just a matter of making a directory for your97board in arch/sh/boards/ and adding rules to hook your board in with the98build system (more on this in the next section). However, for board families99it makes more sense to have a common top-level arch/sh/boards/ directory100and 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.102 103After you have setup your new arch/sh/boards/ directory, remember that you104should also add a directory in include/asm-sh for headers localized to this105board (if there are going to be more than one). In order to interoperate106seamlessly with the build system, it's best to have this directory the same107as the arch/sh/boards/ directory name, though if your board is again part of108a family, the build system has ways of dealing with this (via incdir-y109overloading), and you can feel free to name the directory after the family110member itself.111 112There are a few things that each board is required to have, both in the113arch/sh/boards and the include/asm-sh/ hierarchy. In order to better114explain this, we use some examples for adding an imaginary board. For115setup code, we're required at the very least to provide definitions for116get_system_type() and platform_setup(). For our imaginary board, this117might look something like::118 119 /*120 * arch/sh/boards/vapor/setup.c - Setup code for imaginary board121 */122 #include <linux/init.h>123 124 const char *get_system_type(void)125 {126 return "FooTech Vaporboard";127 }128 129 int __init platform_setup(void)130 {131 /*132 * If our hardware actually existed, we would do real133 * setup here. Though it's also sane to leave this empty134 * if there's no real init work that has to be done for135 * this board.136 */137 138 /* Start-up imaginary PCI ... */139 140 /* And whatever else ... */141 142 return 0;143 }144 145Our new imaginary board will also have to tie into the machvec in order for it146to be of any use.147 148machvec functions fall into a number of categories:149 150 - 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 DMA156 handles).157 158There are machvec functions added and removed over time, so always be sure to159consult include/asm-sh/machvec.h for the current state of the machvec.160 161The kernel will automatically wrap in generic routines for undefined function162pointers in the machvec at boot time, as machvec functions are referenced163unconditionally throughout most of the tree. Some boards have incredibly164sparse machvecs (such as the dreamcast and sh03), whereas others must define165virtually everything (rts7751r2d).166 167Adding a new machine is relatively trivial (using vapor as an example):168 169If the board-specific definitions are quite minimalistic, as is the case for170the vast majority of boards, simply having a single board-specific header is171sufficient.172 173 - add a new file include/asm-sh/vapor.h which contains prototypes for174 any machine specific IO functions prefixed with the machine name, for175 example vapor_inb. These will be needed when filling out the machine176 vector.177 178 Note that these prototypes are generated automatically by setting179 __IO_PREFIX to something sensible. A typical example would be::180 181 #define __IO_PREFIX vapor182 #include <asm/io_generic.h>183 184 somewhere in the board-specific header. Any boards being ported that still185 have a legacy io.h should remove it entirely and switch to the new model.186 187 - Add machine vector definitions to the board's setup.c. At a bare minimum,188 this must be defined as something like::189 190 struct sh_machine_vector mv_vapor __initmv = {191 .mv_name = "vapor",192 };193 ALIAS_MV(vapor)194 195 - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of196 the machine specific io functions (if there are enough to warrant it).197 1983. Hooking into the Build System199================================200 201Now that we have the corresponding directories setup, and all of the202board-specific code is in place, it's time to look at how to get the203whole mess to fit into the build system.204 205Large portions of the build system are now entirely dynamic, and merely206require the proper entry here and there in order to get things done.207 208The first thing to do is to add an entry to arch/sh/Kconfig, under the209"System type" menu::210 211 config SH_VAPOR212 bool "Vapor"213 help214 select Vapor if configuring for a FooTech Vaporboard.215 216next, this has to be added into arch/sh/Makefile. All boards require a217machdir-y entry in order to be built. This entry needs to be the name of218the board directory as it appears in arch/sh/boards, even if it is in a219sub-directory (in which case, all parent directories below arch/sh/boards/220need to be listed). For our new board, this entry can look like::221 222 machdir-$(CONFIG_SH_VAPOR) += vapor223 224provided that we've placed everything in the arch/sh/boards/vapor/ directory.225 226Next, the build system assumes that your include/asm-sh directory will also227be named the same. If this is not the case (as is the case with multiple228boards belonging to a common family), then the directory name needs to be229implicitly appended to incdir-y. The existing code manages this for the230Solution Engine and hp6xx boards, so see these for an example.231 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-types234list. The method for doing this is self explanatory, and so we won't waste235space restating it here. After this is done, you will be able to use236implicit checks for your board if you need this somewhere throughout the237common code, such as::238 239 /* Make sure we're on the FooTech Vaporboard */240 if (!mach_is_vapor())241 return -ENODEV;242 243also note that the mach_is_boardname() check will be implicitly forced to244lowercase, regardless of the fact that the mach-types entries are all245uppercase. You can read the script if you really care, but it's pretty ugly,246so you probably don't want to do that.247 248Now all that's left to do is providing a defconfig for your new board. This249way, other people who end up with this board can simply use this config250for reference instead of trying to guess what settings are supposed to be251used on it.252 253Also, as soon as you have copied over a sample .config for your new board254(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a255build target, and it will be implicitly listed as such in the help text.256 257Looking at the 'make help' output, you should now see something like:258 259Architecture specific targets (sh):260 261 ======================= =============================================262 zImage Compressed kernel image (arch/sh/boot/zImage)263 adx_defconfig Build for adx264 cqreek_defconfig Build for cqreek265 dreamcast_defconfig Build for dreamcast266 ...267 vapor_defconfig Build for vapor268 ======================= =============================================269 270which then allows you to do::271 272 $ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux273 274which will in turn copy the defconfig for this board, run it through275oldconfig (prompting you for any new options since the time of creation),276and start you on your way to having a functional kernel for your new277board.278