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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

1	
2	                Adding a new board to LinuxSH
3	               ================================
4	
5	               Paul Mundt <lethal@linux-sh.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	
53	... and so on. Headers for the companion chips are treated the same way as
54	board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the
55	hd64461-specific headers.
56	
57	Finally, 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	
82	It should be noted that CPU subtypes are _not_ abstracted. Thus, these still
83	need to be dealt with by the CPU family specific code.
84	
85	2. Adding a New Board
86	=====================
87	
88	The first thing to determine is whether the board you are adding will be
89	isolated, or whether it will be part of a family of boards that can mostly
90	share the same board-specific code with minor differences.
91	
92	In the first case, this is just a matter of making a directory for your
93	board in arch/sh/boards/ and adding rules to hook your board in with the
94	build system (more on this in the next section). However, for board families
95	it makes more sense to have a common top-level arch/sh/boards/ directory
96	and then populate that with sub-directories for each member of the family.
97	Both the Solution Engine and the hp6xx boards are an example of this.
98	
99	After you have setup your new arch/sh/boards/ directory, remember that you
100	should also add a directory in include/asm-sh for headers localized to this
101	board (if there are going to be more than one). In order to interoperate
102	seamlessly with the build system, it's best to have this directory the same
103	as the arch/sh/boards/ directory name, though if your board is again part of
104	a family, the build system has ways of dealing with this (via incdir-y
105	overloading), and you can feel free to name the directory after the family
106	member itself.
107	
108	There are a few things that each board is required to have, both in the
109	arch/sh/boards and the include/asm-sh/ hierarchy. In order to better
110	explain this, we use some examples for adding an imaginary board. For
111	setup code, we're required at the very least to provide definitions for
112	get_system_type() and platform_setup(). For our imaginary board, this
113	might look something like:
114	
115	/*
116	 * arch/sh/boards/vapor/setup.c - Setup code for imaginary board
117	 */
118	#include <linux/init.h>
119	#include <asm/rtc.h> /* for board_time_init() */
120	
121	const char *get_system_type(void)
122	{
123		return "FooTech Vaporboard";
124	}
125	
126	int __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	
149	Our new imaginary board will also have to tie into the machvec in order for it
150	to be of any use.
151	
152	machvec functions fall into a number of categories:
153	
154	 - I/O functions to IO memory (inb etc) and PCI/main memory (readb etc).
155	 - 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).
161	
162	There are machvec functions added and removed over time, so always be sure to
163	consult include/asm-sh/machvec.h for the current state of the machvec.
164	
165	The kernel will automatically wrap in generic routines for undefined function
166	pointers in the machvec at boot time, as machvec functions are referenced
167	unconditionally throughout most of the tree. Some boards have incredibly
168	sparse machvecs (such as the dreamcast and sh03), whereas others must define
169	virtually everything (rts7751r2d).
170	
171	Adding a new machine is relatively trivial (using vapor as an example):
172	
173	If the board-specific definitions are quite minimalistic, as is the case for
174	the vast majority of boards, simply having a single board-specific header is
175	sufficient.
176	
177	 - add a new file include/asm-sh/vapor.h which contains prototypes for
178	   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	
182	   Note that these prototypes are generated automatically by setting
183	   __IO_PREFIX to something sensible. A typical example would be:
184	
185		#define __IO_PREFIX vapor
186	   	#include <asm/io_generic.h>
187	
188	   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.
190	
191	 - Add machine vector definitions to the board's setup.c. At a bare minimum,
192	   this must be defined as something like:
193	
194		struct sh_machine_vector mv_vapor __initmv = {
195			.mv_name = "vapor",
196		};
197		ALIAS_MV(vapor)
198	
199	 - 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).
201	
202	3. Hooking into the Build System
203	================================
204	
205	Now that we have the corresponding directories setup, and all of the
206	board-specific code is in place, it's time to look at how to get the
207	whole mess to fit into the build system.
208	
209	Large portions of the build system are now entirely dynamic, and merely
210	require the proper entry here and there in order to get things done.
211	
212	The first thing to do is to add an entry to arch/sh/Kconfig, under the
213	"System type" menu:
214	
215	config SH_VAPOR
216		bool "Vapor"
217		help
218		  select Vapor if configuring for a FooTech Vaporboard.
219	
220	next, this has to be added into arch/sh/Makefile. All boards require a
221	machdir-y entry in order to be built. This entry needs to be the name of
222	the board directory as it appears in arch/sh/boards, even if it is in a
223	sub-directory (in which case, all parent directories below arch/sh/boards/
224	need to be listed). For our new board, this entry can look like:
225	
226	machdir-$(CONFIG_SH_VAPOR)	+= vapor
227	
228	provided that we've placed everything in the arch/sh/boards/vapor/ directory.
229	
230	Next, the build system assumes that your include/asm-sh directory will also
231	be named the same. If this is not the case (as is the case with multiple
232	boards belonging to a common family), then the directory name needs to be
233	implicitly appended to incdir-y. The existing code manages this for the
234	Solution Engine and hp6xx boards, so see these for an example.
235	
236	Once that is taken care of, it's time to add an entry for the mach type.
237	This is done by adding an entry to the end of the arch/sh/tools/mach-types
238	list. The method for doing this is self explanatory, and so we won't waste
239	space restating it here. After this is done, you will be able to use
240	implicit checks for your board if you need this somewhere throughout the
241	common code, such as:
242	
243		/* Make sure we're on the FooTech Vaporboard */
244		if (!mach_is_vapor())
245			return -ENODEV;
246	
247	also note that the mach_is_boardname() check will be implicitly forced to
248	lowercase, regardless of the fact that the mach-types entries are all
249	uppercase. You can read the script if you really care, but it's pretty ugly,
250	so you probably don't want to do that.
251	
252	Now all that's left to do is providing a defconfig for your new board. This
253	way, other people who end up with this board can simply use this config
254	for reference instead of trying to guess what settings are supposed to be
255	used on it.
256	
257	Also, 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
259	build target, and it will be implicitly listed as such in the help text.
260	
261	Looking at the 'make help' output, you should now see something like:
262	
263	Architecture 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	
271	which then allows you to do:
272	
273	$ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux
274	
275	which will in turn copy the defconfig for this board, run it through
276	oldconfig (prompting you for any new options since the time of creation),
277	and start you on your way to having a functional kernel for your new
278	board.
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