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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
Paul Mundt3eeebf12008-10-28 20:07:44 +090050 `-- hd64461
Linus Torvalds1da177e2005-04-16 15:20:36 -070051 `-- 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
Paul Mundt801e0452006-09-27 16:15:48 +0900100should 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.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107
108There are a few things that each board is required to have, both in the
Uwe Kleine-König1b3c3712007-02-17 19:23:03 +0100109arch/sh/boards and the include/asm-sh/ hierarchy. In order to better
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110explain 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>
Paul Mundt801e0452006-09-27 16:15:48 +0900119#include <asm/rtc.h> /* for board_time_init() */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120
121const char *get_system_type(void)
122{
123 return "FooTech Vaporboard";
124}
125
126int __init platform_setup(void)
127{
128 /*
129 * If our hardware actually existed, we would do real
130 * setup here. Though it's also sane to leave this empty
131 * if there's no real init work that has to be done for
132 * this board.
133 */
134
135 /*
136 * Presume all FooTech boards have the same broken timer,
137 * and also presume that we've defined foo_timer_init to
138 * do something useful.
139 */
140 board_time_init = foo_timer_init;
141
142 /* Start-up imaginary PCI ... */
143
144 /* And whatever else ... */
145
146 return 0;
147}
148
149Our new imaginary board will also have to tie into the machvec in order for it
Paul Mundt801e0452006-09-27 16:15:48 +0900150to be of any use.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151
152machvec functions fall into a number of categories:
153
154 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc).
Paul Mundt801e0452006-09-27 16:15:48 +0900155 - I/O mapping functions (ioport_map, ioport_unmap, etc).
156 - a 'heartbeat' function.
157 - PCI and IRQ initialization routines.
158 - Consistent allocators (for boards that need special allocators,
159 particularly for allocating out of some board-specific SRAM for DMA
160 handles).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161
Paul Mundt801e0452006-09-27 16:15:48 +0900162There are machvec functions added and removed over time, so always be sure to
163consult include/asm-sh/machvec.h for the current state of the machvec.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164
Paul Mundt801e0452006-09-27 16:15:48 +0900165The kernel will automatically wrap in generic routines for undefined function
166pointers in the machvec at boot time, as machvec functions are referenced
167unconditionally throughout most of the tree. Some boards have incredibly
168sparse machvecs (such as the dreamcast and sh03), whereas others must define
169virtually everything (rts7751r2d).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
Paul Mundt801e0452006-09-27 16:15:48 +0900171Adding a new machine is relatively trivial (using vapor as an example):
Linus Torvalds1da177e2005-04-16 15:20:36 -0700172
Paul Mundt801e0452006-09-27 16:15:48 +0900173If the board-specific definitions are quite minimalistic, as is the case for
174the vast majority of boards, simply having a single board-specific header is
175sufficient.
176
177 - add a new file include/asm-sh/vapor.h which contains prototypes for
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178 any machine specific IO functions prefixed with the machine name, for
179 example vapor_inb. These will be needed when filling out the machine
180 vector.
181
Paul Mundt801e0452006-09-27 16:15:48 +0900182 Note that these prototypes are generated automatically by setting
183 __IO_PREFIX to something sensible. A typical example would be:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700184
Paul Mundt801e0452006-09-27 16:15:48 +0900185 #define __IO_PREFIX vapor
186 #include <asm/io_generic.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700187
Paul Mundt801e0452006-09-27 16:15:48 +0900188 somewhere in the board-specific header. Any boards being ported that still
189 have a legacy io.h should remove it entirely and switch to the new model.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190
Paul Mundt801e0452006-09-27 16:15:48 +0900191 - Add machine vector definitions to the board's setup.c. At a bare minimum,
192 this must be defined as something like:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193
Paul Mundt801e0452006-09-27 16:15:48 +0900194 struct sh_machine_vector mv_vapor __initmv = {
195 .mv_name = "vapor",
196 };
197 ALIAS_MV(vapor)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700198
Paul Mundt801e0452006-09-27 16:15:48 +0900199 - finally add a file arch/sh/boards/vapor/io.c, which contains definitions of
200 the machine specific io functions (if there are enough to warrant it).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700201
2023. Hooking into the Build System
203================================
204
205Now that we have the corresponding directories setup, and all of the
206board-specific code is in place, it's time to look at how to get the
207whole mess to fit into the build system.
208
209Large portions of the build system are now entirely dynamic, and merely
210require the proper entry here and there in order to get things done.
211
212The first thing to do is to add an entry to arch/sh/Kconfig, under the
213"System type" menu:
214
215config SH_VAPOR
216 bool "Vapor"
217 help
218 select Vapor if configuring for a FooTech Vaporboard.
219
220next, this has to be added into arch/sh/Makefile. All boards require a
221machdir-y entry in order to be built. This entry needs to be the name of
222the board directory as it appears in arch/sh/boards, even if it is in a
223sub-directory (in which case, all parent directories below arch/sh/boards/
224need to be listed). For our new board, this entry can look like:
225
226machdir-$(CONFIG_SH_VAPOR) += vapor
227
228provided that we've placed everything in the arch/sh/boards/vapor/ directory.
229
230Next, the build system assumes that your include/asm-sh directory will also
231be named the same. If this is not the case (as is the case with multiple
232boards belonging to a common family), then the directory name needs to be
233implicitly appended to incdir-y. The existing code manages this for the
234Solution Engine and hp6xx boards, so see these for an example.
235
236Once that is taken care of, it's time to add an entry for the mach type.
237This is done by adding an entry to the end of the arch/sh/tools/mach-types
238list. The method for doing this is self explanatory, and so we won't waste
239space restating it here. After this is done, you will be able to use
240implicit checks for your board if you need this somewhere throughout the
241common code, such as:
242
243 /* Make sure we're on the FooTech Vaporboard */
244 if (!mach_is_vapor())
245 return -ENODEV;
246
247also note that the mach_is_boardname() check will be implicitly forced to
248lowercase, regardless of the fact that the mach-types entries are all
249uppercase. You can read the script if you really care, but it's pretty ugly,
250so you probably don't want to do that.
251
252Now all that's left to do is providing a defconfig for your new board. This
253way, other people who end up with this board can simply use this config
254for reference instead of trying to guess what settings are supposed to be
255used on it.
256
257Also, as soon as you have copied over a sample .config for your new board
258(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a
259build target, and it will be implicitly listed as such in the help text.
260
261Looking at the 'make help' output, you should now see something like:
262
263Architecture specific targets (sh):
264 zImage - Compressed kernel image (arch/sh/boot/zImage)
265 adx_defconfig - Build for adx
266 cqreek_defconfig - Build for cqreek
267 dreamcast_defconfig - Build for dreamcast
268...
269 vapor_defconfig - Build for vapor
270
271which then allows you to do:
272
273$ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux
274
275which will in turn copy the defconfig for this board, run it through
276oldconfig (prompting you for any new options since the time of creation),
277and start you on your way to having a functional kernel for your new
278board.