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, 103 insertions, 0 deletions

diff --git a/Documentation/arch/arm/memory.rst b/Documentation/arch/arm/memory.rst
new file mode 100644
index 000000000000..0cb1e2938823
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@@ -0,0 +1,103 @@
+=================================
+Kernel Memory Layout on ARM Linux
+=================================
+
+		Russell King <rmk@arm.linux.org.uk>
+
+		     November 17, 2005 (2.6.15)
+
+This document describes the virtual memory layout which the Linux
+kernel uses for ARM processors.  It indicates which regions are
+free for platforms to use, and which are used by generic code.
+
+The ARM CPU is capable of addressing a maximum of 4GB virtual memory
+space, and this must be shared between user space processes, the
+kernel, and hardware devices.
+
+As the ARM architecture matures, it becomes necessary to reserve
+certain regions of VM space for use for new facilities; therefore
+this document may reserve more VM space over time.
+
+=============== =============== ===============================================
+Start		End		Use
+=============== =============== ===============================================
+ffff8000	ffffffff	copy_user_page / clear_user_page use.
+				For SA11xx and Xscale, this is used to
+				setup a minicache mapping.
+
+ffff4000	ffffffff	cache aliasing on ARMv6 and later CPUs.
+
+ffff1000	ffff7fff	Reserved.
+				Platforms must not use this address range.
+
+ffff0000	ffff0fff	CPU vector page.
+				The CPU vectors are mapped here if the
+				CPU supports vector relocation (control
+				register V bit.)
+
+fffe0000	fffeffff	XScale cache flush area.  This is used
+				in proc-xscale.S to flush the whole data
+				cache. (XScale does not have TCM.)
+
+fffe8000	fffeffff	DTCM mapping area for platforms with
+				DTCM mounted inside the CPU.
+
+fffe0000	fffe7fff	ITCM mapping area for platforms with
+				ITCM mounted inside the CPU.
+
+ffc80000	ffefffff	Fixmap mapping region.  Addresses provided
+				by fix_to_virt() will be located here.
+
+ffc00000	ffc7ffff	Guard region
+
+ff800000	ffbfffff	Permanent, fixed read-only mapping of the
+				firmware provided DT blob
+
+fee00000	feffffff	Mapping of PCI I/O space. This is a static
+				mapping within the vmalloc space.
+
+VMALLOC_START	VMALLOC_END-1	vmalloc() / ioremap() space.
+				Memory returned by vmalloc/ioremap will
+				be dynamically placed in this region.
+				Machine specific static mappings are also
+				located here through iotable_init().
+				VMALLOC_START is based upon the value
+				of the high_memory variable, and VMALLOC_END
+				is equal to 0xff800000.
+
+PAGE_OFFSET	high_memory-1	Kernel direct-mapped RAM region.
+				This maps the platforms RAM, and typically
+				maps all platform RAM in a 1:1 relationship.
+
+PKMAP_BASE	PAGE_OFFSET-1	Permanent kernel mappings
+				One way of mapping HIGHMEM pages into kernel
+				space.
+
+MODULES_VADDR	MODULES_END-1	Kernel module space
+				Kernel modules inserted via insmod are
+				placed here using dynamic mappings.
+
+TASK_SIZE	MODULES_VADDR-1	KASAn shadow memory when KASan is in use.
+				The range from MODULES_VADDR to the top
+				of the memory is shadowed here with 1 bit
+				per byte of memory.
+
+00001000	TASK_SIZE-1	User space mappings
+				Per-thread mappings are placed here via
+				the mmap() system call.
+
+00000000	00000fff	CPU vector page / null pointer trap
+				CPUs which do not support vector remapping
+				place their vector page here.  NULL pointer
+				dereferences by both the kernel and user
+				space are also caught via this mapping.
+=============== =============== ===============================================
+
+Please note that mappings which collide with the above areas may result
+in a non-bootable kernel, or may cause the kernel to (eventually) panic
+at run time.
+
+Since future CPUs may impact the kernel mapping layout, user programs
+must not access any memory which is not mapped inside their 0x0001000
+to TASK_SIZE address range.  If they wish to access these areas, they
+must set up their own mappings using open() and mmap().