1 files changed, 43 insertions, 8 deletions

diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
index 37fc4f632176..f3c05b5f9f08 100644
--- a/Documentation/arm64/booting.txt
+++ b/Documentation/arm64/booting.txt
@@ -72,27 +72,54 @@ The decompressed kernel image contains a 64-byte header as follows:
 
   u32 code0;                    /* Executable code */
   u32 code1;                    /* Executable code */
-  u64 text_offset;              /* Image load offset */
-  u64 res0      = 0;            /* reserved */
-  u64 res1      = 0;            /* reserved */
+  u64 text_offset;              /* Image load offset, little endian */
+  u64 image_size;               /* Effective Image size, little endian */
+  u64 flags;                    /* kernel flags, little endian */
   u64 res2      = 0;            /* reserved */
   u64 res3      = 0;            /* reserved */
   u64 res4      = 0;            /* reserved */
   u32 magic     = 0x644d5241;   /* Magic number, little endian, "ARM\x64" */
-  u32 res5 = 0;                 /* reserved */
+  u32 res5;                     /* reserved (used for PE COFF offset) */
 
 
 Header notes:
 
+- As of v3.17, all fields are little endian unless stated otherwise.
+
 - code0/code1 are responsible for branching to stext.
+
 - when booting through EFI, code0/code1 are initially skipped.
   res5 is an offset to the PE header and the PE header has the EFI
-  entry point (efi_stub_entry). When the stub has done its work, it
+  entry point (efi_stub_entry).  When the stub has done its work, it
   jumps to code0 to resume the normal boot process.
 
-The image must be placed at the specified offset (currently 0x80000)
-from the start of the system RAM and called there. The start of the
-system RAM must be aligned to 2MB.
+- Prior to v3.17, the endianness of text_offset was not specified.  In
+  these cases image_size is zero and text_offset is 0x80000 in the
+  endianness of the kernel.  Where image_size is non-zero image_size is
+  little-endian and must be respected.  Where image_size is zero,
+  text_offset can be assumed to be 0x80000.
+
+- 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.
+  Bits 1-63:    Reserved.
+
+- When image_size is zero, a bootloader should attempt to keep as much
+  memory as possible free for use by the kernel immediately after the
+  end of the kernel image. The amount of space required will vary
+  depending on selected features, and is effectively unbound.
+
+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.
+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
+memreserve region in the device tree) will be considered as available to
+the kernel.
 
 Before jumping into the kernel, the following conditions must be met:
 
@@ -141,6 +168,14 @@ Before jumping into the kernel, the following conditions must be met:
   the kernel image will be entered must be initialised by software at a
   higher exception level to prevent execution in an UNKNOWN state.
 
+  For systems with a GICv3 interrupt controller:
+  - If EL3 is present:
+    ICC_SRE_EL3.Enable (bit 3) must be initialiased to 0b1.
+    ICC_SRE_EL3.SRE (bit 0) must be initialised to 0b1.
+  - If the kernel is entered at EL1:
+    ICC.SRE_EL2.Enable (bit 3) must be initialised to 0b1
+    ICC_SRE_EL2.SRE (bit 0) must be initialised to 0b1.
+
 The requirements described above for CPU mode, caches, MMUs, architected
 timers, coherency and system registers apply to all CPUs.  All CPUs must
 enter the kernel in the same exception level.