Lines Matching refs:the
10 program that runs before the main kernel. The boot loader is expected
11 to initialise various devices, and eventually call the Linux kernel,
12 passing information to the kernel.
14 Essentially, the boot loader should provide (as a minimum) the
17 1. Setup and initialise the RAM.
19 3. Detect the machine type.
20 4. Setup the kernel tagged list.
22 6. Call the kernel image.
31 The boot loader is expected to find and initialise all RAM that the
32 kernel will use for volatile data storage in the system. It performs
35 the RAM in the machine, or any other method the boot loader designer
45 The boot loader should initialise and enable one serial port on the
46 target. This allows the kernel serial driver to automatically detect
47 which serial port it should use for the kernel console (generally
48 used for debugging purposes, or communication with the target.)
50 As an alternative, the boot loader can pass the relevant 'console='
51 option to the kernel via the tagged lists specifying the port, and
57 3. Detect the machine type
63 The boot loader should detect the machine type its running on by some
65 looks at the connected hardware is beyond the scope of this document.
67 value to the kernel. (see linux/arch/arm/tools/mach-types). This
68 should be passed to the kernel in register r1.
70 For DT-only platforms, the machine type will be determined by device
71 tree. set the machine type to all ones (~0). This is not strictly
81 passing configuration data to the kernel. The physical address of the
82 boot data is passed to the kernel in register r2.
84 4a. Setup the kernel tagged list
87 The boot loader must create and initialise the kernel tagged list.
90 has the size field set to '2' (0x00000002). The ATAG_NONE must set
91 the size field to zero.
93 Any number of tags can be placed in the list. It is undefined
94 whether a repeated tag appends to the information carried by the
95 previous tag, or whether it replaces the information in its
96 entirety; some tags behave as the former, others the latter.
98 The boot loader must pass at a minimum the size and location of
99 the system memory, and root filesystem location. Therefore, the
113 the kernel decompressor nor initrd 'bootp' program will overwrite
114 it. The recommended placement is in the first 16KiB of RAM.
116 4b. Setup the device tree
120 at a 64bit aligned address and initialize it with the boot data. The
122 The kernel will look for the dtb magic value of 0xd00dfeed at the dtb
126 The boot loader must pass at a minimum the size and location of the
127 system memory, and the root filesystem location. The dtb must be
128 placed in a region of memory where the kernel decompressor will not
129 overwrite it, whilst remaining within the region which will be covered
130 by the kernel's low-memory mapping.
132 A safe location is just above the 128MiB boundary from start of RAM.
140 If an initramfs is in use then, as with the dtb, it must be placed in
141 a region of memory where the kernel decompressor will not overwrite it
142 while also with the region which will be covered by the kernel's
145 A safe location is just above the device tree blob which itself will
146 be loaded just above the 128MiB boundary from the start of RAM as
149 6. Calling the kernel image
155 There are two options for calling the kernel zImage. If the zImage
157 then it is legal for the boot loader to call the zImage in flash
161 kernel should be placed in the first 128MiB of RAM. It is recommended
162 that it is loaded above 32MiB in order to avoid the need to relocate
163 prior to decompression, which will make the boot process slightly
166 When booting a raw (non-zImage) kernel the constraints are tighter.
167 In this case the kernel must be loaded at an offset into system equal
170 In any case, the following conditions must be met:
185 For CPUs which do not include the ARM virtualization extensions, the
188 CPUs which include support for the virtualization extensions can be
189 entered in HYP mode in order to enable the kernel to make full use of
190 these extensions. This is the recommended boot method for such CPUs,
191 unless the virtualisations are already in use by a pre-installed
194 If the kernel is not entered in HYP mode for any reason, it must be
202 If the kernel is entered in HYP mode, the above requirements apply to
203 the HYP mode configuration in addition to the ordinary PL1 (privileged
204 kernel modes) configuration. In addition, all traps into the
207 possible. Except for entering in HYP mode, the system configuration
208 should be such that a kernel which does not include support for the
211 - The boot loader is expected to call the kernel image by jumping
212 directly to the first instruction of the kernel image.
214 On CPUs supporting the ARM instruction set, the entry must be
217 On CPUs supporting only the Thumb instruction set such as
218 Cortex-M class CPUs, the entry must be made in Thumb state.