Fixed MTP to work with TWRP

Documentation/sh/new-machine.txt

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+
+                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>
+#include <asm/rtc.h> /* for board_time_init() */
+
+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.
+	 */
+
+  	/* 
+	 * Presume all FooTech boards have the same broken timer,
+	 * and also presume that we've defined foo_timer_init to
+	 * do something useful.
+	 */
+  	board_time_init = foo_timer_init;
+
+	/* 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.

Documentation/sh/register-banks.txt

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+	Notes on register bank usage in the kernel
+	==========================================
+
+Introduction
+------------
+
+The SH-3 and SH-4 CPU families traditionally include a single partial register
+bank (selected by SR.RB, only r0 ... r7 are banked), whereas other families
+may have more full-featured banking or simply no such capabilities at all.
+
+SR.RB banking
+-------------
+
+In the case of this type of banking, banked registers are mapped directly to
+r0 ... r7 if SR.RB is set to the bank we are interested in, otherwise ldc/stc
+can still be used to reference the banked registers (as r0_bank ... r7_bank)
+when in the context of another bank. The developer must keep the SR.RB value
+in mind when writing code that utilizes these banked registers, for obvious
+reasons. Userspace is also not able to poke at the bank1 values, so these can
+be used rather effectively as scratch registers by the kernel.
+
+Presently the kernel uses several of these registers.
+
+	- r0_bank, r1_bank (referenced as k0 and k1, used for scratch
+	  registers when doing exception handling).
+	- r2_bank (used to track the EXPEVT/INTEVT code)
+		- Used by do_IRQ() and friends for doing irq mapping based off
+		  of the interrupt exception vector jump table offset
+	- r6_bank (global interrupt mask)
+		- The SR.IMASK interrupt handler makes use of this to set the
+		  interrupt priority level (used by local_irq_enable())
+	- r7_bank (current)
+