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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
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
Uwe Kleine-König1b3c3712007-02-17 19:23:03 +010020hierarchy looks like the following:
Linus Torvalds1da177e2005-04-16 15:20:36 -070021
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
Linus Torvalds1da177e2005-04-16 15:20:36 -070044Next, 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
56board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the
57hd64461-specific headers.
58
59Finally, 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
84It should be noted that CPU subtypes are _not_ abstracted. Thus, these still
85need to be dealt with by the CPU family specific code.
86
872. Adding a New Board
88=====================
89
90The first thing to determine is whether the board you are adding will be
91isolated, or whether it will be part of a family of boards that can mostly
92share the same board-specific code with minor differences.
93
94In the first case, this is just a matter of making a directory for your
95board in arch/sh/boards/ and adding rules to hook your board in with the
96build system (more on this in the next section). However, for board families
97it makes more sense to have a common top-level arch/sh/boards/ directory
98and then populate that with sub-directories for each member of the family.
99Both the Solution Engine and the hp6xx boards are an example of this.
100
101After you have setup your new arch/sh/boards/ directory, remember that you
Paul Mundt801e0452006-09-27 16:15:48 +0900102should also add a directory in include/asm-sh for headers localized to this
103board (if there are going to be more than one). In order to interoperate
104seamlessly with the build system, it's best to have this directory the same
105as the arch/sh/boards/ directory name, though if your board is again part of
106a family, the build system has ways of dealing with this (via incdir-y
107overloading), and you can feel free to name the directory after the family
108member itself.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700109
110There are a few things that each board is required to have, both in the
Uwe Kleine-König1b3c3712007-02-17 19:23:03 +0100111arch/sh/boards and the include/asm-sh/ hierarchy. In order to better
Linus Torvalds1da177e2005-04-16 15:20:36 -0700112explain this, we use some examples for adding an imaginary board. For
113setup code, we're required at the very least to provide definitions for
114get_system_type() and platform_setup(). For our imaginary board, this
115might look something like:
116
117/*
118 * arch/sh/boards/vapor/setup.c - Setup code for imaginary board
119 */
120#include <linux/init.h>
Paul Mundt801e0452006-09-27 16:15:48 +0900121#include <asm/rtc.h> /* for board_time_init() */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700122
123const char *get_system_type(void)
124{
125 return "FooTech Vaporboard";
126}
127
128int __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
151Our new imaginary board will also have to tie into the machvec in order for it
Paul Mundt801e0452006-09-27 16:15:48 +0900152to be of any use.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153
154machvec functions fall into a number of categories:
155
156 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc).
Paul Mundt801e0452006-09-27 16:15:48 +0900157 - 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).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163
Paul Mundt801e0452006-09-27 16:15:48 +0900164There are machvec functions added and removed over time, so always be sure to
165consult include/asm-sh/machvec.h for the current state of the machvec.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166
Paul Mundt801e0452006-09-27 16:15:48 +0900167The kernel will automatically wrap in generic routines for undefined function
168pointers in the machvec at boot time, as machvec functions are referenced
169unconditionally throughout most of the tree. Some boards have incredibly
170sparse machvecs (such as the dreamcast and sh03), whereas others must define
171virtually everything (rts7751r2d).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700172
Paul Mundt801e0452006-09-27 16:15:48 +0900173Adding a new machine is relatively trivial (using vapor as an example):
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174
Paul Mundt801e0452006-09-27 16:15:48 +0900175If the board-specific definitions are quite minimalistic, as is the case for
176the vast majority of boards, simply having a single board-specific header is
177sufficient.
178
179 - add a new file include/asm-sh/vapor.h which contains prototypes for
Linus Torvalds1da177e2005-04-16 15:20:36 -0700180 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
Paul Mundt801e0452006-09-27 16:15:48 +0900184 Note that these prototypes are generated automatically by setting
185 __IO_PREFIX to something sensible. A typical example would be:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186
Paul Mundt801e0452006-09-27 16:15:48 +0900187 #define __IO_PREFIX vapor
188 #include <asm/io_generic.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189
Paul Mundt801e0452006-09-27 16:15:48 +0900190 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.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192
Paul Mundt801e0452006-09-27 16:15:48 +0900193 - Add machine vector definitions to the board's setup.c. At a bare minimum,
194 this must be defined as something like:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700195
Paul Mundt801e0452006-09-27 16:15:48 +0900196 struct sh_machine_vector mv_vapor __initmv = {
197 .mv_name = "vapor",
198 };
199 ALIAS_MV(vapor)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200
Paul Mundt801e0452006-09-27 16:15:48 +0900201 - 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).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203
2043. Hooking into the Build System
205================================
206
207Now that we have the corresponding directories setup, and all of the
208board-specific code is in place, it's time to look at how to get the
209whole mess to fit into the build system.
210
211Large portions of the build system are now entirely dynamic, and merely
212require the proper entry here and there in order to get things done.
213
214The first thing to do is to add an entry to arch/sh/Kconfig, under the
215"System type" menu:
216
217config SH_VAPOR
218 bool "Vapor"
219 help
220 select Vapor if configuring for a FooTech Vaporboard.
221
222next, this has to be added into arch/sh/Makefile. All boards require a
223machdir-y entry in order to be built. This entry needs to be the name of
224the board directory as it appears in arch/sh/boards, even if it is in a
225sub-directory (in which case, all parent directories below arch/sh/boards/
226need to be listed). For our new board, this entry can look like:
227
228machdir-$(CONFIG_SH_VAPOR) += vapor
229
230provided that we've placed everything in the arch/sh/boards/vapor/ directory.
231
232Next, the build system assumes that your include/asm-sh directory will also
233be named the same. If this is not the case (as is the case with multiple
234boards belonging to a common family), then the directory name needs to be
235implicitly appended to incdir-y. The existing code manages this for the
236Solution Engine and hp6xx boards, so see these for an example.
237
238Once that is taken care of, it's time to add an entry for the mach type.
239This is done by adding an entry to the end of the arch/sh/tools/mach-types
240list. The method for doing this is self explanatory, and so we won't waste
241space restating it here. After this is done, you will be able to use
242implicit checks for your board if you need this somewhere throughout the
243common code, such as:
244
245 /* Make sure we're on the FooTech Vaporboard */
246 if (!mach_is_vapor())
247 return -ENODEV;
248
249also note that the mach_is_boardname() check will be implicitly forced to
250lowercase, regardless of the fact that the mach-types entries are all
251uppercase. You can read the script if you really care, but it's pretty ugly,
252so you probably don't want to do that.
253
254Now all that's left to do is providing a defconfig for your new board. This
255way, other people who end up with this board can simply use this config
256for reference instead of trying to guess what settings are supposed to be
257used on it.
258
259Also, 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
261build target, and it will be implicitly listed as such in the help text.
262
263Looking at the 'make help' output, you should now see something like:
264
265Architecture 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
273which then allows you to do:
274
275$ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux
276
277which will in turn copy the defconfig for this board, run it through
278oldconfig (prompting you for any new options since the time of creation),
279and start you on your way to having a functional kernel for your new
280board.