arm: docs: Move Arm documentation to Documentation/arch/

Architecture-specific documentation is being moved into Documentation/arch/
as a way of cleaning up the top-level documentation directory and making
the docs hierarchy more closely match the source hierarchy.  Move
Documentation/arm into arch/ (along with the Chinese equvalent
translations).

Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
Cc: Samuel Holland <samuel@sholland.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Alim Akhtar <alim.akhtar@samsung.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Acked-by: Alexandre TORGUE <alexandre.torgue@foss.st.com>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 268 deletions

diff --git a/Documentation/arm/kernel_user_helpers.rst b/Documentation/arm/kernel_user_helpers.rst
deleted file mode 100644
index eb6f3d916622..000000000000
--- a/Documentation/arm/kernel_user_helpers.rst
+++ /dev/null
@@ -1,268 +0,0 @@
-============================
-Kernel-provided User Helpers
-============================
-
-These are segment of kernel provided user code reachable from user space
-at a fixed address in kernel memory.  This is used to provide user space
-with some operations which require kernel help because of unimplemented
-native feature and/or instructions in many ARM CPUs. The idea is for this
-code to be executed directly in user mode for best efficiency but which is
-too intimate with the kernel counter part to be left to user libraries.
-In fact this code might even differ from one CPU to another depending on
-the available instruction set, or whether it is a SMP systems. In other
-words, the kernel reserves the right to change this code as needed without
-warning. Only the entry points and their results as documented here are
-guaranteed to be stable.
-
-This is different from (but doesn't preclude) a full blown VDSO
-implementation, however a VDSO would prevent some assembly tricks with
-constants that allows for efficient branching to those code segments. And
-since those code segments only use a few cycles before returning to user
-code, the overhead of a VDSO indirect far call would add a measurable
-overhead to such minimalistic operations.
-
-User space is expected to bypass those helpers and implement those things
-inline (either in the code emitted directly by the compiler, or part of
-the implementation of a library call) when optimizing for a recent enough
-processor that has the necessary native support, but only if resulting
-binaries are already to be incompatible with earlier ARM processors due to
-usage of similar native instructions for other things.  In other words
-don't make binaries unable to run on earlier processors just for the sake
-of not using these kernel helpers if your compiled code is not going to
-use new instructions for other purpose.
-
-New helpers may be added over time, so an older kernel may be missing some
-helpers present in a newer kernel.  For this reason, programs must check
-the value of __kuser_helper_version (see below) before assuming that it is
-safe to call any particular helper.  This check should ideally be
-performed only once at process startup time, and execution aborted early
-if the required helpers are not provided by the kernel version that
-process is running on.
-
-kuser_helper_version
---------------------
-
-Location:	0xffff0ffc
-
-Reference declaration::
-
-  extern int32_t __kuser_helper_version;
-
-Definition:
-
-  This field contains the number of helpers being implemented by the
-  running kernel.  User space may read this to determine the availability
-  of a particular helper.
-
-Usage example::
-
-  #define __kuser_helper_version (*(int32_t *)0xffff0ffc)
-
-  void check_kuser_version(void)
-  {
-	if (__kuser_helper_version < 2) {
-		fprintf(stderr, "can't do atomic operations, kernel too old\n");
-		abort();
-	}
-  }
-
-Notes:
-
-  User space may assume that the value of this field never changes
-  during the lifetime of any single process.  This means that this
-  field can be read once during the initialisation of a library or
-  startup phase of a program.
-
-kuser_get_tls
--------------
-
-Location:	0xffff0fe0
-
-Reference prototype::
-
-  void * __kuser_get_tls(void);
-
-Input:
-
-  lr = return address
-
-Output:
-
-  r0 = TLS value
-
-Clobbered registers:
-
-  none
-
-Definition:
-
-  Get the TLS value as previously set via the __ARM_NR_set_tls syscall.
-
-Usage example::
-
-  typedef void * (__kuser_get_tls_t)(void);
-  #define __kuser_get_tls (*(__kuser_get_tls_t *)0xffff0fe0)
-
-  void foo()
-  {
-	void *tls = __kuser_get_tls();
-	printf("TLS = %p\n", tls);
-  }
-
-Notes:
-
-  - Valid only if __kuser_helper_version >= 1 (from kernel version 2.6.12).
-
-kuser_cmpxchg
--------------
-
-Location:	0xffff0fc0
-
-Reference prototype::
-
-  int __kuser_cmpxchg(int32_t oldval, int32_t newval, volatile int32_t *ptr);
-
-Input:
-
-  r0 = oldval
-  r1 = newval
-  r2 = ptr
-  lr = return address
-
-Output:
-
-  r0 = success code (zero or non-zero)
-  C flag = set if r0 == 0, clear if r0 != 0
-
-Clobbered registers:
-
-  r3, ip, flags
-
-Definition:
-
-  Atomically store newval in `*ptr` only if `*ptr` is equal to oldval.
-  Return zero if `*ptr` was changed or non-zero if no exchange happened.
-  The C flag is also set if `*ptr` was changed to allow for assembly
-  optimization in the calling code.
-
-Usage example::
-
-  typedef int (__kuser_cmpxchg_t)(int oldval, int newval, volatile int *ptr);
-  #define __kuser_cmpxchg (*(__kuser_cmpxchg_t *)0xffff0fc0)
-
-  int atomic_add(volatile int *ptr, int val)
-  {
-	int old, new;
-
-	do {
-		old = *ptr;
-		new = old + val;
-	} while(__kuser_cmpxchg(old, new, ptr));
-
-	return new;
-  }
-
-Notes:
-
-  - This routine already includes memory barriers as needed.
-
-  - Valid only if __kuser_helper_version >= 2 (from kernel version 2.6.12).
-
-kuser_memory_barrier
---------------------
-
-Location:	0xffff0fa0
-
-Reference prototype::
-
-  void __kuser_memory_barrier(void);
-
-Input:
-
-  lr = return address
-
-Output:
-
-  none
-
-Clobbered registers:
-
-  none
-
-Definition:
-
-  Apply any needed memory barrier to preserve consistency with data modified
-  manually and __kuser_cmpxchg usage.
-
-Usage example::
-
-  typedef void (__kuser_dmb_t)(void);
-  #define __kuser_dmb (*(__kuser_dmb_t *)0xffff0fa0)
-
-Notes:
-
-  - Valid only if __kuser_helper_version >= 3 (from kernel version 2.6.15).
-
-kuser_cmpxchg64
----------------
-
-Location:	0xffff0f60
-
-Reference prototype::
-
-  int __kuser_cmpxchg64(const int64_t *oldval,
-                        const int64_t *newval,
-                        volatile int64_t *ptr);
-
-Input:
-
-  r0 = pointer to oldval
-  r1 = pointer to newval
-  r2 = pointer to target value
-  lr = return address
-
-Output:
-
-  r0 = success code (zero or non-zero)
-  C flag = set if r0 == 0, clear if r0 != 0
-
-Clobbered registers:
-
-  r3, lr, flags
-
-Definition:
-
-  Atomically store the 64-bit value pointed by `*newval` in `*ptr` only if `*ptr`
-  is equal to the 64-bit value pointed by `*oldval`.  Return zero if `*ptr` was
-  changed or non-zero if no exchange happened.
-
-  The C flag is also set if `*ptr` was changed to allow for assembly
-  optimization in the calling code.
-
-Usage example::
-
-  typedef int (__kuser_cmpxchg64_t)(const int64_t *oldval,
-                                    const int64_t *newval,
-                                    volatile int64_t *ptr);
-  #define __kuser_cmpxchg64 (*(__kuser_cmpxchg64_t *)0xffff0f60)
-
-  int64_t atomic_add64(volatile int64_t *ptr, int64_t val)
-  {
-	int64_t old, new;
-
-	do {
-		old = *ptr;
-		new = old + val;
-	} while(__kuser_cmpxchg64(&old, &new, ptr));
-
-	return new;
-  }
-
-Notes:
-
-  - This routine already includes memory barriers as needed.
-
-  - Due to the length of this sequence, this spans 2 conventional kuser
-    "slots", therefore 0xffff0f80 is not used as a valid entry point.
-
-  - Valid only if __kuser_helper_version >= 5 (from kernel version 3.1).