Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. 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.