diff options
Diffstat (limited to 'kernel/Documentation/arm64/booting.txt')
| -rw-r--r-- | kernel/Documentation/arm64/booting.txt | 39 |
1 files changed, 29 insertions, 10 deletions
diff --git a/kernel/Documentation/arm64/booting.txt b/kernel/Documentation/arm64/booting.txt index f3c05b5f9..701d39d31 100644 --- a/kernel/Documentation/arm64/booting.txt +++ b/kernel/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 ------------------------------ @@ -79,7 +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: @@ -101,8 +103,13 @@ 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. - Bits 1-63: Reserved. + Bit 0: Kernel endianness. 1 if BE, 0 if LE. + Bit 1-2: Kernel Page size. + 0 - Unspecified. + 1 - 4K + 2 - 16K + 3 - 64K + Bits 3-63: 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 @@ -113,11 +120,14 @@ 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. @@ -168,13 +178,22 @@ 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: + For systems with a GICv3 interrupt controller to be used in v3 mode: - 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 DT or ACPI tables must describe a GICv3 interrupt controller. + + For systems with a GICv3 interrupt controller to be used in + compatibility (v2) mode: + - If EL3 is present: + ICC_SRE_EL3.SRE (bit 0) must be initialised to 0b0. + - If the kernel is entered at EL1: + ICC_SRE_EL2.SRE (bit 0) must be initialised to 0b0. + - The DT or ACPI tables must describe a GICv2 interrupt controller. The requirements described above for CPU mode, caches, MMUs, architected timers, coherency and system registers apply to all CPUs. All CPUs must |