Passing boot parameters to the kernel¶

Boot parameters are represented as a TLV list in the memory. Please seearch/xtensa/include/asm/bootparam.h for definition of the bp_tag structure andtag value constants. First entry in the list must have type BP_TAG_FIRST, lastentry must have type BP_TAG_LAST. The address of the first list entry ispassed to the kernel in the register a2. The address type depends on MMU type:

• For configurations without MMU, with region protection or with MPU theaddress must be the physical address.
• For configurations with region translarion MMU or with MMUv3 and CONFIG_MMU=nthe address must be a valid address in the current mapping. The kernel willnot change the mapping on its own.
• For configurations with MMUv2 the address must be a virtual address in thedefault virtual mapping (0xd0000000..0xffffffff).
• For configurations with MMUv3 and CONFIG_MMU=y the address may be either avirtual or physical address. In either case it must be within the defaultvirtual mapping. It is considered physical if it is within the range ofphysical addresses covered by the default KSEG mapping (XCHAL_KSEG_PADDR..XCHAL_KSEG_PADDR + XCHAL_KSEG_SIZE), otherwise it is considered virtual.