path: root/Documentation/arm
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authorArd Biesheuvel <>2020-10-11 10:21:37 +0100
committerRussell King <>2020-10-27 12:11:01 +0000
commit7a1be318f5795cb66fa0dc86b3ace427fe68057f (patch)
treea84f9c1b2418a33837d53dbc0ce3e242e401dcfc /Documentation/arm
parente9a2f8b599d0bc22a1b13e69527246ac39c697b4 (diff)
ARM: 9012/1: move device tree mapping out of linear region
On ARM, setting up the linear region is tricky, given the constraints around placement and alignment of the memblocks, and how the kernel itself as well as the DT are placed in physical memory. Let's simplify matters a bit, by moving the device tree mapping to the top of the address space, right between the end of the vmalloc region and the start of the the fixmap region, and create a read-only mapping for it that is independent of the size of the linear region, and how it is organized. Since this region was formerly used as a guard region, which will now be populated fully on LPAE builds by this read-only mapping (which will still be able to function as a guard region for stray writes), bump the start of the [underutilized] fixmap region by 512 KB as well, to ensure that there is always a proper guard region here. Doing so still leaves ample room for the fixmap space, even with NR_CPUS set to its maximum value of 32. Tested-by: Linus Walleij <> Reviewed-by: Linus Walleij <> Reviewed-by: Nicolas Pitre <> Signed-off-by: Ard Biesheuvel <> Signed-off-by: Russell King <>
Diffstat (limited to 'Documentation/arm')
1 files changed, 6 insertions, 1 deletions
diff --git a/Documentation/arm/memory.rst b/Documentation/arm/memory.rst
index 0521b4ce5c96..34bb23c44a71 100644
--- a/Documentation/arm/memory.rst
+++ b/Documentation/arm/memory.rst
@@ -45,9 +45,14 @@ fffe8000 fffeffff DTCM mapping area for platforms with
fffe0000 fffe7fff ITCM mapping area for platforms with
ITCM mounted inside the CPU.
-ffc00000 ffefffff Fixmap mapping region. Addresses provided
+ffc80000 ffefffff Fixmap mapping region. Addresses provided
by fix_to_virt() will be located here.
+ffc00000 ffc7ffff Guard region
+ff800000 ffbfffff Permanent, fixed read-only mapping of the
+ firmware provided DT blob
fee00000 feffffff Mapping of PCI I/O space. This is a static
mapping within the vmalloc space.