[mirror_ubuntu-jammy-kernel.git] / Documentation / mips / booting.rst

.. SPDX-License-Identifier: GPL-2.0

BMIPS DeviceTree Booting
------------------------

  Some bootloaders only support a single entry point, at the start of the
  kernel image.  Other bootloaders will jump to the ELF start address.
  Both schemes are supported; CONFIG_BOOT_RAW=y and CONFIG_NO_EXCEPT_FILL=y,
  so the first instruction immediately jumps to kernel_entry().

  Similar to the arch/arm case (b), a DT-aware bootloader is expected to
  set up the following registers:

         a0 : 0

         a1 : 0xffffffff

         a2 : Physical pointer to the device tree block (defined in chapter
         II) in RAM.  The device tree can be located anywhere in the first
         512MB of the physical address space (0x00000000 - 0x1fffffff),
         aligned on a 64 bit boundary.

  Legacy bootloaders do not use this convention, and they do not pass in a
  DT block.  In this case, Linux will look for a builtin DTB, selected via
  CONFIG_DT_*.

  This convention is defined for 32-bit systems only, as there are not
  currently any 64-bit BMIPS implementations.
Commit	Line	Data
44184828 RH	1	.. SPDX-License-Identifier: GPL-2.0
	2
	3	BMIPS DeviceTree Booting
	4	------------------------
	5
	6	Some bootloaders only support a single entry point, at the start of the
	7	kernel image. Other bootloaders will jump to the ELF start address.
	8	Both schemes are supported; CONFIG_BOOT_RAW=y and CONFIG_NO_EXCEPT_FILL=y,
	9	so the first instruction immediately jumps to kernel_entry().
	10
	11	Similar to the arch/arm case (b), a DT-aware bootloader is expected to
	12	set up the following registers:
	13
	14	a0 : 0
	15
	16	a1 : 0xffffffff
	17
	18	a2 : Physical pointer to the device tree block (defined in chapter
	19	II) in RAM. The device tree can be located anywhere in the first
	20	512MB of the physical address space (0x00000000 - 0x1fffffff),
	21	aligned on a 64 bit boundary.
	22
	23	Legacy bootloaders do not use this convention, and they do not pass in a
	24	DT block. In this case, Linux will look for a builtin DTB, selected via
	25	CONFIG_DT_*.
	26
	27	This convention is defined for 32-bit systems only, as there are not
	28	currently any 64-bit BMIPS implementations.