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| -rw-r--r-- | doc/README.arm64 | 27 |
1 files changed, 17 insertions, 10 deletions
diff --git a/doc/README.arm64 b/doc/README.arm64 index f658fa2..b0bba0f 100644 --- a/doc/README.arm64 +++ b/doc/README.arm64 @@ -2,23 +2,31 @@ 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 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. -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 @@ -37,9 +45,8 @@ Notes aarch32 specific codes. - -Contributor -=========== +Contributors +============ Tom Rini <trini@ti.com> Scott Wood <scottwood@freescale.com> York Sun <yorksun@freescale.com> |