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authorJ. Bruce Fields <bfields@redhat.com>2012-10-09 18:35:22 -0400
committerJ. Bruce Fields <bfields@redhat.com>2012-10-09 18:35:22 -0400
commitf474af7051212b4efc8267583fad9c4ebf33ccff (patch)
tree1aa46ebc8065a341f247c2a2d9af2f624ad1d4f8 /Documentation/arm64/booting.txt
parent0d22f68f02c10d5d10ec5712917e5828b001a822 (diff)
parente3dd9a52cb5552c46c2a4ca7ccdfb4dab5c72457 (diff)
nfs: disintegrate UAPI for nfs
This is to complete part of the Userspace API (UAPI) disintegration for which the preparatory patches were pulled recently. After these patches, userspace headers will be segregated into: include/uapi/linux/.../foo.h for the userspace interface stuff, and: include/linux/.../foo.h for the strictly kernel internal stuff. Signed-off-by: J. Bruce Fields <bfields@redhat.com>
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+ Booting AArch64 Linux
+ =====================
+
+Author: Will Deacon <will.deacon@arm.com>
+Date : 07 September 2012
+
+This document is based on the ARM booting document by Russell King and
+is relevant to all public releases of the AArch64 Linux kernel.
+
+The AArch64 exception model is made up of a number of exception levels
+(EL0 - EL3), with EL0 and EL1 having a secure and a non-secure
+counterpart. EL2 is the hypervisor level and exists only in non-secure
+mode. EL3 is the highest priority level and exists only in secure mode.
+
+For the purposes of this document, we will use the term `boot loader'
+simply to define all software that executes on the CPU(s) before control
+is passed to the Linux kernel. This may include secure monitor and
+hypervisor code, or it may just be a handful of instructions for
+preparing a minimal boot environment.
+
+Essentially, the boot loader should provide (as a minimum) the
+following:
+
+1. Setup and initialise the RAM
+2. Setup the device tree
+3. Decompress the kernel image
+4. Call the kernel image
+
+
+1. Setup and initialise RAM
+---------------------------
+
+Requirement: MANDATORY
+
+The boot loader is expected to find and initialise all RAM that the
+kernel will use for volatile data storage in the system. It performs
+this in a machine dependent manner. (It may use internal algorithms
+to automatically locate and size all RAM, or it may use knowledge of
+the RAM in the machine, or any other method the boot loader designer
+sees fit.)
+
+
+2. Setup the device tree
+-------------------------
+
+Requirement: MANDATORY
+
+The device tree blob (dtb) must be no bigger than 2 megabytes in size
+and placed at a 2-megabyte boundary within the first 512 megabytes from
+the start of the kernel image. This is to allow the kernel to map the
+blob using a single section mapping in the initial page tables.
+
+
+3. Decompress the kernel image
+------------------------------
+
+Requirement: OPTIONAL
+
+The AArch64 kernel does not currently provide a decompressor and
+therefore requires decompression (gzip etc.) to be performed by the boot
+loader if a compressed Image target (e.g. Image.gz) is used. For
+bootloaders that do not implement this requirement, the uncompressed
+Image target is available instead.
+
+
+4. Call the kernel image
+------------------------
+
+Requirement: MANDATORY
+
+The decompressed kernel image contains a 32-byte header as follows:
+
+ u32 magic = 0x14000008; /* branch to stext, little-endian */
+ u32 res0 = 0; /* reserved */
+ u64 text_offset; /* Image load offset */
+ u64 res1 = 0; /* reserved */
+ u64 res2 = 0; /* reserved */
+
+The image must be placed at the specified offset (currently 0x80000)
+from the start of the system RAM and called there. The start of the
+system RAM must be aligned to 2MB.
+
+Before jumping into the kernel, the following conditions must be met:
+
+- Quiesce all DMA capable devices so that memory does not get
+ corrupted by bogus network packets or disk data. This will save
+ you many hours of debug.
+
+- Primary CPU general-purpose register settings
+ x0 = physical address of device tree blob (dtb) in system RAM.
+ x1 = 0 (reserved for future use)
+ x2 = 0 (reserved for future use)
+ x3 = 0 (reserved for future use)
+
+- CPU mode
+ All forms of interrupts must be masked in PSTATE.DAIF (Debug, SError,
+ IRQ and FIQ).
+ The CPU must be in either EL2 (RECOMMENDED in order to have access to
+ the virtualisation extensions) or non-secure EL1.
+
+- Caches, MMUs
+ The MMU must be off.
+ Instruction cache may be on or off.
+ Data cache must be off and invalidated.
+ External caches (if present) must be configured and disabled.
+
+- Architected timers
+ CNTFRQ must be programmed with the timer frequency.
+ If entering the kernel at EL1, CNTHCTL_EL2 must have EL1PCTEN (bit 0)
+ set where available.
+
+- Coherency
+ All CPUs to be booted by the kernel must be part of the same coherency
+ domain on entry to the kernel. This may require IMPLEMENTATION DEFINED
+ initialisation to enable the receiving of maintenance operations on
+ each CPU.
+
+- System registers
+ All writable architected system registers at the exception level where
+ the kernel image will be entered must be initialised by software at a
+ higher exception level to prevent execution in an UNKNOWN state.
+
+The boot loader is expected to enter the kernel on each CPU in the
+following manner:
+
+- The primary CPU must jump directly to the first instruction of the
+ kernel image. The device tree blob passed by this CPU must contain
+ for each CPU node:
+
+ 1. An 'enable-method' property. Currently, the only supported value
+ for this field is the string "spin-table".
+
+ 2. A 'cpu-release-addr' property identifying a 64-bit,
+ zero-initialised memory location.
+
+ It is expected that the bootloader will generate these device tree
+ properties and insert them into the blob prior to kernel entry.
+
+- Any secondary CPUs must spin outside of the kernel in a reserved area
+ of memory (communicated to the kernel by a /memreserve/ region in the
+ device tree) polling their cpu-release-addr location, which must be
+ contained in the reserved region. A wfe instruction may be inserted
+ to reduce the overhead of the busy-loop and a sev will be issued by
+ the primary CPU. When a read of the location pointed to by the
+ cpu-release-addr returns a non-zero value, the CPU must jump directly
+ to this value.
+
+- Secondary CPU general-purpose register settings
+ x0 = 0 (reserved for future use)
+ x1 = 0 (reserved for future use)
+ x2 = 0 (reserved for future use)
+ x3 = 0 (reserved for future use)