Commit 801e0458 authored by Paul Mundt's avatar Paul Mundt

sh: Update new-machine.txt so it's more accurate.

This fell behind a bit, get it updated so the documentation
has something in common with reality.
Signed-off-by: default avatarPaul Mundt <lethal@linux-sh.org>
parent a328ff9a
......@@ -41,11 +41,6 @@ Board-specific code:
|
.. more boards here ...
It should also be noted that each board is required to have some certain
headers. At the time of this writing, io.h is the only thing that needs
to be provided for each board, and can generally just reference generic
functions (with the exception of isa_port2addr).
Next, for companion chips:
.
`-- arch
......@@ -104,12 +99,13 @@ 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
also must add a directory in include/asm-sh for headers localized to this
board. 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, and you can feel free to name the directory after
the family member itself.
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/ heirarchy. In order to better
......@@ -122,6 +118,7 @@ might look something like:
* arch/sh/boards/vapor/setup.c - Setup code for imaginary board
*/
#include <linux/init.h>
#include <asm/rtc.h> /* for board_time_init() */
const char *get_system_type(void)
{
......@@ -152,79 +149,57 @@ int __init platform_setup(void)
}
Our new imaginary board will also have to tie into the machvec in order for it
to be of any use. Currently the machvec is slowly on its way out, but is still
required for the time being. As such, let us take a look at what needs to be
done for the machvec assignment.
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 remapping functions (ioremap etc)
- some initialisation functions
- a 'heartbeat' function
- some miscellaneous flags
The tree can be built in two ways:
- as a fully generic build. All drivers are linked in, and all functions
go through the machvec
- as a machine specific build. In this case only the required drivers
will be linked in, and some macros may be redefined to not go through
the machvec where performance is important (in particular IO functions).
There are three ways in which IO can be performed:
- none at all. This is really only useful for the 'unknown' machine type,
which us designed to run on a machine about which we know nothing, and
so all all IO instructions do nothing.
- fully custom. In this case all IO functions go to a machine specific
set of functions which can do what they like
- a generic set of functions. These will cope with most situations,
and rely on a single function, mv_port2addr, which is called through the
machine vector, and converts an IO address into a memory address, which
can be read from/written to directly.
Thus adding a new machine involves the following steps (I will assume I am
adding a machine called vapor):
- add a new file include/asm-sh/vapor/io.h which contains prototypes for
- 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.
This is the minimum that is required, however there are ample
opportunities to optimise this. In particular, by making the prototypes
inline function definitions, it is possible to inline the function when
building machine specific versions. Note that the machine vector
functions will still be needed, so that a module built for a generic
setup can be loaded.
- add a new file arch/sh/boards/vapor/mach.c. This contains the definition
of the machine vector. When building the machine specific version, this
will be the real machine vector (via an alias), while in the generic
version is used to initialise the machine vector, and then freed, by
making it initdata. This should be defined as:
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.
A note about initialisation functions. Three initialisation functions are
provided in the machine vector:
- mv_arch_init - called very early on from setup_arch
- mv_init_irq - called from init_IRQ, after the generic SH interrupt
initialisation
- mv_init_pci - currently not used
Any other remaining functions which need to be called at start up can be
added to the list using the __initcalls macro (or module_init if the code
can be built as a module). Many generic drivers probe to see if the device
they are targeting is present, however this may not always be appropriate,
so a flag can be added to the machine vector which will be set on those
machines which have the hardware in question, reducing the probe to a
single conditional.
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
================================
......@@ -303,4 +278,3 @@ 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.
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