Merge git://git.denx.de/u-boot-i2c

[people/ms/u-boot.git] / doc / README.arm64

diff --git a/doc/README.arm64 b/doc/README.arm64
index f32108feb77cec5dd67f8dbb6557fbb4a8f3a180..b0bba0fc65e4634c602fdab7627e0d7b4ba4758f 100644 (file)
--- a/doc/README.arm64
+++ b/doc/README.arm64
@@ -1,24 +1,32 @@
-U-boot for arm64
+U-Boot for arm64
 
 Summary
 =======
-No hardware platform of arm64 is available now. The u-boot is
-simulated on Foundation Model and Fast Model for ARMv8.
+The initial arm64 U-Boot port was developed before hardware was available,
+so the first supported platforms were the Foundation and Fast Model for ARMv8.
+These days U-Boot runs on a variety of 64-bit capable ARM hardware, from
+embedded development boards to servers.
 
 Notes
 =====
 
-1. Currenly, u-boot run at the highest exception level processor
-   supported and jump to EL2 or optionally EL1 before enter OS.
+1. U-Boot can run at any exception level it is entered in, it is
+   recommened to enter it in EL3 if U-Boot takes some responsibilities of a
+   classical firmware (like initial hardware setup, CPU errata workarounds
+   or SMP bringup). U-Boot can be entered in EL2 when its main purpose is
+   that of a boot loader. It can drop to lower exception levels before
+   entering the OS.
 
-2. U-boot for arm64 is compiled with AArch64-gcc. AArch64-gcc
+2. U-Boot for arm64 is compiled with AArch64-gcc. AArch64-gcc
    use rela relocation format, a tool(tools/relocate-rela) by Scott Wood
    is used to encode the initial addend of rela to u-boot.bin. After running,
-   the u-boot will be relocated to destination again.
+   the U-Boot will be relocated to destination again.
 
-3. Fdt should be placed at a 2-megabyte boundary and within the first 512
-   megabytes from the start of the kernel image. So, fdt_high should be
-   defined specially.
+3. Earlier Linux kernel versions required the FDT to be placed at a
+   2 MB boundary and within the same 512 MB section as the kernel image,
+   resulting in fdt_high to be defined specially.
+   Since kernel version 4.2 Linux is more relaxed about the DT location, so it
+   can be placed anywhere in memory.
    Please reference linux/Documentation/arm64/booting.txt for detail.
 
 4. Spin-table is used to wake up secondary processors. One location
@@ -36,30 +44,9 @@ Notes
 6. CONFIG_ARM64 instead of CONFIG_ARMV8 is used to distinguish aarch64 and
    aarch32 specific codes.
 
-7. CONFIG_SYS_FULL_VA is used to enable 2-level page tables. For cores
-   supporting 64k pages it allows usage of full 48+ virtual/physical addresses
 
-   Enabling this option requires the following ones to be defined:
-       - CONFIG_SYS_MEM_MAP - an array of 'struct mm_region' describing the
-         system memory map (start, length, attributes)
-       - CONFIG_SYS_MEM_MAP_SIZE - number of entries in CONFIG_SYS_MEM_MAP
-       - CONFIG_SYS_PTL1_ENTRIES - number of 1st level page table entries
-       - CONFIG_SYS_PTL2_ENTRIES - number of 1nd level page table entries
-         for the largest CONFIG_SYS_MEM_MAP entry
-       - CONFIG_COREID_MASK - the mask value used to get the core from the
-         MPIDR_EL1 register
-       - CONFIG_SYS_PTL2_BITS - number of bits addressed by the 2nd level
-         page tables
-       - CONFIG_SYS_BLOCK_SHIFT - number of bits addressed by a single block
-         entry from L2 page tables
-       - CONFIG_SYS_PGTABLE_SIZE - total size of the page table
-       - CONFIG_SYS_TCR_EL{1,2,3}_IPS_BITS - the IPS field of the TCR_EL{1,2,3}
-
-
-
-
-Contributor
-===========
+Contributors
+============
    Tom Rini            <trini@ti.com>
    Scott Wood          <scottwood@freescale.com>
    York Sun            <yorksun@freescale.com>