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arm64/Documentation: clarify wording regarding memory below the Image

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Clarify that the memory below the start of the image but inside the
region covered by the linear mapping has no special significance to
the kernel, and may be used by the firmware provided that it is marked
as reserved.

Also, fix up some whitespace errors.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel 2015-07-29 12:30:39 +01:00 committed by Will Deacon
parent 484c96dbb2
commit 6c020ea8dc
1 changed files with 7 additions and 4 deletions
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11
Documentation/arm64/booting.txt
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@ -81,7 +81,7 @@ The decompressed kernel image contains a 64-byte header as follows:
u64 res3 = 0; /* reserved */
u64 res4 = 0; /* reserved */
u32 magic = 0x644d5241; /* Magic number, little endian, "ARM\x64" */
u32 res5; /* reserved (used for PE COFF offset) */
u32 res5; /* reserved (used for PE COFF offset) */
Header notes:
@ -103,7 +103,7 @@ Header notes:
- The flags field (introduced in v3.17) is a little-endian 64-bit field
composed as follows:
Bit 0: Kernel endianness. 1 if BE, 0 if LE.
Bit 0: Kernel endianness. 1 if BE, 0 if LE.
Bits 1-63: Reserved.
- When image_size is zero, a bootloader should attempt to keep as much
@ -115,11 +115,14 @@ The Image must be placed text_offset bytes from a 2MB aligned base
address near the start of usable system RAM and called there. Memory
below that base address is currently unusable by Linux, and therefore it
is strongly recommended that this location is the start of system RAM.
The region between the 2 MB aligned base address and the start of the
image has no special significance to the kernel, and may be used for
other purposes.
At least image_size bytes from the start of the image must be free for
use by the kernel.
Any memory described to the kernel (even that below the 2MB aligned base
address) which is not marked as reserved from the kernel e.g. with a
Any memory described to the kernel (even that below the start of the
image) which is not marked as reserved from the kernel (e.g., with a
memreserve region in the device tree) will be considered as available to
the kernel.