arch/arm/booting.rst

9 The following documentation is relevant to 2.4.18-rmk6 and beyond.
11 In order to boot ARM Linux, you require a boot loader, which is a small
12 program that runs before the main kernel.  The boot loader is expected
16 Essentially, the boot loader should provide (as a minimum) the
28 ---------------------------
30 Existing boot loaders:
32 New boot loaders:
35 The boot loader is expected to find and initialise all RAM that the
39 the RAM in the machine, or any other method the boot loader designer
44 -----------------------------
46 Existing boot loaders:
48 New boot loaders:
51 The boot loader should initialise and enable one serial port on the
56 As an alternative, the boot loader can pass the relevant 'console='
60        Documentation/admin-guide/kernel-parameters.rst.
64 --------------------------
66 Existing boot loaders:
68 New boot loaders:
69 	MANDATORY except for DT-only platforms
71 The boot loader should detect the machine type its running on by some
72 method.  Whether this is a hard coded value or some algorithm that
74 The boot loader must ultimately be able to provide a MACH_TYPE_xxx
75 value to the kernel. (see linux/arch/arm/tools/mach-types).  This
78 For DT-only platforms, the machine type will be determined by device
82 4. Setup boot data
83 ------------------
85 Existing boot loaders:
87 New boot loaders:
90 The boot loader must provide either a tagged list or a dtb image for
92 boot data is passed to the kernel in register r2.
95 --------------------------------
97 The boot loader must create and initialise the kernel tagged list.
108 The boot loader must pass at a minimum the size and location of
112 		+-----------+
113   base ->	| ATAG_CORE |  |
114 		+-----------+  |
116 		+-----------+  |
118 		+-----------+  v
127 -------------------------
129 The boot loader must load a device tree image (dtb) into system ram
130 at a 64bit aligned address and initialize it with the boot data.  The
136 The boot loader must pass at a minimum the size and location of the
140 by the kernel's low-memory mapping.
145 ------------------
147 Existing boot loaders:
149 New boot loaders:
155 low-memory mapping.
162 ---------------------------
164 Existing boot loaders:
166 New boot loaders:
171 then it is legal for the boot loader to call the zImage in flash
177 prior to decompression, which will make the boot process slightly
180 When booting a raw (non-zImage) kernel the constraints are tighter.
182 to TEXT_OFFSET - PAGE_OFFSET.
186 - Quiesce all DMA capable devices so that memory does not get
190 - CPU register settings
192   - r0 = 0,
193   - r1 = machine type number discovered in (3) above.
194   - r2 = physical address of tagged list in system RAM, or
197 - CPU mode
206   these extensions.  This is the recommended boot method for such CPUs,
207   unless the virtualisations are already in use by a pre-installed
213 - Caches, MMUs
228   virtualization extensions can boot correctly without extra help.
230 - The boot loader is expected to call the kernel image by jumping
234   made in ARM state, even for a Thumb-2 kernel.
237   Cortex-M class CPUs, the entry must be made in Thumb state.