arch/arm/booting.rst

2 Booting ARM Linux
9 The following documentation is relevant to 2.4.18-rmk6 and beyond.
28 ---------------------------
38 to automatically locate and size all RAM, or it may use knowledge of
44 -----------------------------
60        Documentation/admin-guide/kernel-parameters.rst.
64 --------------------------
69 	MANDATORY except for DT-only platforms
73 looks at the connected hardware is beyond the scope of this document.
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
83 ------------------
91 passing configuration data to the kernel.  The physical address of the
95 --------------------------------
103 Any number of tags can be placed in the list.  It is undefined
108 The boot loader must pass at a minimum the size and location of
112 		+-----------+
113   base ->	| ATAG_CORE |  |
114 		+-----------+  |
116 		+-----------+  |
118 		+-----------+  v
122 The tagged list must be placed in a region of memory where neither
124 it.  The recommended placement is in the first 16KiB of RAM.
127 -------------------------
132 The kernel will look for the dtb magic value of 0xd00dfeed at the dtb
133 physical address to determine if a dtb has been passed instead of a
136 The boot loader must pass at a minimum the size and location of the
138 placed in a region of memory where the kernel decompressor will not
140 by the kernel's low-memory mapping.
142 A safe location is just above the 128MiB boundary from start of RAM.
145 ------------------
153 a region of memory where the kernel decompressor will not overwrite it
155 low-memory mapping.
158 be loaded just above the 128MiB boundary from the start of RAM as
162 ---------------------------
175 kernel should be placed in the first 128MiB of RAM.  It is recommended
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
188   you many hours of debug.
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
195     physical address of device tree block (dtb) in system RAM
197 - CPU mode
199   All forms of interrupts must be disabled (IRQs and FIQs)
205   entered in HYP mode in order to enable the kernel to make full use of
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
231   directly to the first instruction of the kernel image.
234   made in ARM state, even for a Thumb-2 kernel.
237   Cortex-M class CPUs, the entry must be made in Thumb state.