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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2015-06-01 13:40:32 +0200
committerCatalin Marinas <catalin.marinas@arm.com>2015-06-02 16:31:33 +0100
commit61bd93ce801bb6df36eda257a9d2d16c02863cdd (patch)
treeca3bb08e7b2e8223ca612e51fd44c4e0fd7e1670 /Documentation/arm64/booting.txt
parent24bbd929e6b9e62afd263c42b4318d3b603c956c (diff)
arm64: use fixmap region for permanent FDT mapping
Currently, the FDT blob needs to be in the same 512 MB region as the kernel, so that it can be mapped into the kernel virtual memory space very early on using a minimal set of statically allocated translation tables. Now that we have early fixmap support, we can relax this restriction, by moving the permanent FDT mapping to the fixmap region instead. This way, the FDT blob may be anywhere in memory. This also moves the vetting of the FDT to mmu.c, since the early init code in head.S does not handle mapping of the FDT anymore. At the same time, fix up some comments in head.S that have gone stale. Reviewed-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'Documentation/arm64/booting.txt')
-rw-r--r--Documentation/arm64/booting.txt10
1 files changed, 6 insertions, 4 deletions
diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
index f3c05b5f9f08..1690350f16e7 100644
--- a/Documentation/arm64/booting.txt
+++ b/Documentation/arm64/booting.txt
@@ -45,11 +45,13 @@ sees fit.)
Requirement: MANDATORY
-The device tree blob (dtb) must be placed on an 8-byte boundary within
-the first 512 megabytes from the start of the kernel image and must not
-cross a 2-megabyte boundary. This is to allow the kernel to map the
-blob using a single section mapping in the initial page tables.
+The device tree blob (dtb) must be placed on an 8-byte boundary and must
+not exceed 2 megabytes in size. Since the dtb will be mapped cacheable
+using blocks of up to 2 megabytes in size, it must not be placed within
+any 2M region which must be mapped with any specific attributes.
+NOTE: versions prior to v4.2 also require that the DTB be placed within
+the 512 MB region starting at text_offset bytes below the kernel Image.
3. Decompress the kernel image
------------------------------