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authorMax Filippov <jcmvbkbc@gmail.com>2018-11-15 04:48:07 +0300
committerMax Filippov <jcmvbkbc@gmail.com>2019-02-04 05:06:19 +0300
commit05bdebd546db924f9bcb4c524c436a016b0c8fca (patch)
tree07137e96d783776a74a229fba43ac41274a7e29b /Documentation/xtensa
parent8834f5600cf3c8db365e18a3d5cac2c2780c81e5 (diff)
downloadlinux-05bdebd546db924f9bcb4c524c436a016b0c8fca.tar.xz
xtensa: document boot parameter passing
Add booting.txt to Documentation/xtensa with description of boot parameters representation and passing to the kernel. Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Diffstat (limited to 'Documentation/xtensa')
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diff --git a/Documentation/xtensa/booting.txt b/Documentation/xtensa/booting.txt
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+Passing boot parameters to the kernel.
+
+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.