[mirror_ubuntu-hirsute-kernel.git] / Documentation / xtensa / booting.rst

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Passing boot parameters to the kernel
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Boot parameters are represented as a TLV list in the memory. Please see
arch/xtensa/include/asm/bootparam.h for definition of the bp_tag structure and
tag value constants. First entry in the list must have type BP_TAG_FIRST, last
entry must have type BP_TAG_LAST. The address of the first list entry is
passed to the kernel in the register a2. The address type depends on MMU type:

- For configurations without MMU, with region protection or with MPU the
  address must be the physical address.
- For configurations with region translarion MMU or with MMUv3 and CONFIG_MMU=n
  the address must be a valid address in the current mapping. The kernel will
  not change the mapping on its own.
- For configurations with MMUv2 the address must be a virtual address in the
  default virtual mapping (0xd0000000..0xffffffff).
- For configurations with MMUv3 and CONFIG_MMU=y the address may be either a
  virtual or physical address. In either case it must be within the default
  virtual mapping. It is considered physical if it is within the range of
  physical addresses covered by the default KSEG mapping (XCHAL_KSEG_PADDR..
  XCHAL_KSEG_PADDR + XCHAL_KSEG_SIZE), otherwise it is considered virtual.
Commit	Line	Data
8ea0afa3 MCC	1	=====================================
	2	Passing boot parameters to the kernel
	3	=====================================
05bdebd5 MF	4
	5	Boot parameters are represented as a TLV list in the memory. Please see
	6	arch/xtensa/include/asm/bootparam.h for definition of the bp_tag structure and
	7	tag value constants. First entry in the list must have type BP_TAG_FIRST, last
	8	entry must have type BP_TAG_LAST. The address of the first list entry is
	9	passed to the kernel in the register a2. The address type depends on MMU type:
8ea0afa3	10
05bdebd5 MF	11	- For configurations without MMU, with region protection or with MPU the
	12	address must be the physical address.
	13	- For configurations with region translarion MMU or with MMUv3 and CONFIG_MMU=n
	14	the address must be a valid address in the current mapping. The kernel will
	15	not change the mapping on its own.
	16	- For configurations with MMUv2 the address must be a virtual address in the
	17	default virtual mapping (0xd0000000..0xffffffff).
	18	- For configurations with MMUv3 and CONFIG_MMU=y the address may be either a
	19	virtual or physical address. In either case it must be within the default
	20	virtual mapping. It is considered physical if it is within the range of
	21	physical addresses covered by the default KSEG mapping (XCHAL_KSEG_PADDR..
	22	XCHAL_KSEG_PADDR + XCHAL_KSEG_SIZE), otherwise it is considered virtual.