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diff --git a/Documentation/arch/sh/new-machine.rst b/Documentation/arch/sh/new-machine.rst new file mode 100644 index 000000000000..e501c52b3b30 --- /dev/null +++ b/Documentation/arch/sh/new-machine.rst @@ -0,0 +1,277 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================= +Adding a new board to LinuxSH +============================= + + Paul Mundt <lethal@linux-sh.org> + +This document attempts to outline what steps are necessary to add support +for new boards to the LinuxSH port under the new 2.5 and 2.6 kernels. This +also attempts to outline some of the noticeable changes between the 2.4 +and the 2.5/2.6 SH backend. + +1. New Directory Structure +========================== + +The first thing to note is the new directory structure. Under 2.4, most +of the board-specific code (with the exception of stboards) ended up +in arch/sh/kernel/ directly, with board-specific headers ending up in +include/asm-sh/. For the new kernel, things are broken out by board type, +companion chip type, and CPU type. Looking at a tree view of this directory +hierarchy looks like the following: + +Board-specific code:: + + . + |-- arch + | `-- sh + | `-- boards + | |-- adx + | | `-- board-specific files + | |-- bigsur + | | `-- board-specific files + | | + | ... more boards here ... + | + `-- include + `-- asm-sh + |-- adx + | `-- board-specific headers + |-- bigsur + | `-- board-specific headers + | + .. more boards here ... + +Next, for companion chips:: + + . + `-- arch + `-- sh + `-- cchips + `-- hd6446x + `-- hd64461 + `-- cchip-specific files + +... and so on. Headers for the companion chips are treated the same way as +board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the +hd64461-specific headers. + +Finally, CPU family support is also abstracted:: + + . + |-- arch + | `-- sh + | |-- kernel + | | `-- cpu + | | |-- sh2 + | | | `-- SH-2 generic files + | | |-- sh3 + | | | `-- SH-3 generic files + | | `-- sh4 + | | `-- SH-4 generic files + | `-- mm + | `-- This is also broken out per CPU family, so each family can + | have their own set of cache/tlb functions. + | + `-- include + `-- asm-sh + |-- cpu-sh2 + | `-- SH-2 specific headers + |-- cpu-sh3 + | `-- SH-3 specific headers + `-- cpu-sh4 + `-- SH-4 specific headers + +It should be noted that CPU subtypes are _not_ abstracted. Thus, these still +need to be dealt with by the CPU family specific code. + +2. Adding a New Board +===================== + +The first thing to determine is whether the board you are adding will be +isolated, or whether it will be part of a family of boards that can mostly +share the same board-specific code with minor differences. + +In the first case, this is just a matter of making a directory for your +board in arch/sh/boards/ and adding rules to hook your board in with the +build system (more on this in the next section). However, for board families +it makes more sense to have a common top-level arch/sh/boards/ directory +and then populate that with sub-directories for each member of the family. +Both the Solution Engine and the hp6xx boards are an example of this. + +After you have setup your new arch/sh/boards/ directory, remember that you +should also add a directory in include/asm-sh for headers localized to this +board (if there are going to be more than one). In order to interoperate +seamlessly with the build system, it's best to have this directory the same +as the arch/sh/boards/ directory name, though if your board is again part of +a family, the build system has ways of dealing with this (via incdir-y +overloading), and you can feel free to name the directory after the family +member itself. + +There are a few things that each board is required to have, both in the +arch/sh/boards and the include/asm-sh/ hierarchy. In order to better +explain this, we use some examples for adding an imaginary board. For +setup code, we're required at the very least to provide definitions for +get_system_type() and platform_setup(). For our imaginary board, this +might look something like:: + + /* + * arch/sh/boards/vapor/setup.c - Setup code for imaginary board + */ + #include <linux/init.h> + + const char *get_system_type(void) + { + return "FooTech Vaporboard"; + } + + int __init platform_setup(void) + { + /* + * If our hardware actually existed, we would do real + * setup here. Though it's also sane to leave this empty + * if there's no real init work that has to be done for + * this board. + */ + + /* Start-up imaginary PCI ... */ + + /* And whatever else ... */ + + return 0; + } + +Our new imaginary board will also have to tie into the machvec in order for it +to be of any use. + +machvec functions fall into a number of categories: + + - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc). + - I/O mapping functions (ioport_map, ioport_unmap, etc). + - a 'heartbeat' function. + - PCI and IRQ initialization routines. + - Consistent allocators (for boards that need special allocators, + particularly for allocating out of some board-specific SRAM for DMA + handles). + +There are machvec functions added and removed over time, so always be sure to +consult include/asm-sh/machvec.h for the current state of the machvec. + +The kernel will automatically wrap in generic routines for undefined function +pointers in the machvec at boot time, as machvec functions are referenced +unconditionally throughout most of the tree. Some boards have incredibly +sparse machvecs (such as the dreamcast and sh03), whereas others must define +virtually everything (rts7751r2d). + +Adding a new machine is relatively trivial (using vapor as an example): + +If the board-specific definitions are quite minimalistic, as is the case for +the vast majority of boards, simply having a single board-specific header is +sufficient. + + - add a new file include/asm-sh/vapor.h which contains prototypes for + any machine specific IO functions prefixed with the machine name, for + example vapor_inb. These will be needed when filling out the machine + vector. + + Note that these prototypes are generated automatically by setting + __IO_PREFIX to something sensible. A typical example would be:: + + #define __IO_PREFIX vapor + #include <asm/io_generic.h> + + somewhere in the board-specific header. Any boards being ported that still + have a legacy io.h should remove it entirely and switch to the new model. + + - Add machine vector definitions to the board's setup.c. At a bare minimum, + this must be defined as something like:: + + struct sh_machine_vector mv_vapor __initmv = { + .mv_name = "vapor", + }; + ALIAS_MV(vapor) + + - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of + the machine specific io functions (if there are enough to warrant it). + +3. Hooking into the Build System +================================ + +Now that we have the corresponding directories setup, and all of the +board-specific code is in place, it's time to look at how to get the +whole mess to fit into the build system. + +Large portions of the build system are now entirely dynamic, and merely +require the proper entry here and there in order to get things done. + +The first thing to do is to add an entry to arch/sh/Kconfig, under the +"System type" menu:: + + config SH_VAPOR + bool "Vapor" + help + select Vapor if configuring for a FooTech Vaporboard. + +next, this has to be added into arch/sh/Makefile. All boards require a +machdir-y entry in order to be built. This entry needs to be the name of +the board directory as it appears in arch/sh/boards, even if it is in a +sub-directory (in which case, all parent directories below arch/sh/boards/ +need to be listed). For our new board, this entry can look like:: + + machdir-$(CONFIG_SH_VAPOR) += vapor + +provided that we've placed everything in the arch/sh/boards/vapor/ directory. + +Next, the build system assumes that your include/asm-sh directory will also +be named the same. If this is not the case (as is the case with multiple +boards belonging to a common family), then the directory name needs to be +implicitly appended to incdir-y. The existing code manages this for the +Solution Engine and hp6xx boards, so see these for an example. + +Once that is taken care of, it's time to add an entry for the mach type. +This is done by adding an entry to the end of the arch/sh/tools/mach-types +list. The method for doing this is self explanatory, and so we won't waste +space restating it here. After this is done, you will be able to use +implicit checks for your board if you need this somewhere throughout the +common code, such as:: + + /* Make sure we're on the FooTech Vaporboard */ + if (!mach_is_vapor()) + return -ENODEV; + +also note that the mach_is_boardname() check will be implicitly forced to +lowercase, regardless of the fact that the mach-types entries are all +uppercase. You can read the script if you really care, but it's pretty ugly, +so you probably don't want to do that. + +Now all that's left to do is providing a defconfig for your new board. This +way, other people who end up with this board can simply use this config +for reference instead of trying to guess what settings are supposed to be +used on it. + +Also, as soon as you have copied over a sample .config for your new board +(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a +build target, and it will be implicitly listed as such in the help text. + +Looking at the 'make help' output, you should now see something like: + +Architecture specific targets (sh): + + ======================= ============================================= + zImage Compressed kernel image (arch/sh/boot/zImage) + adx_defconfig Build for adx + cqreek_defconfig Build for cqreek + dreamcast_defconfig Build for dreamcast + ... + vapor_defconfig Build for vapor + ======================= ============================================= + +which then allows you to do:: + + $ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux + +which will in turn copy the defconfig for this board, run it through +oldconfig (prompting you for any new options since the time of creation), +and start you on your way to having a functional kernel for your new +board. |