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@@ -2,23 +2,31 @@ U-Boot for arm64
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Summary
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=======
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-No hardware platform of arm64 is available now. The U-Boot is
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-simulated on Foundation Model and Fast Model for ARMv8.
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+The initial arm64 U-Boot port was developed before hardware was available,
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+so the first supported platforms were the Foundation and Fast Model for ARMv8.
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+These days U-Boot runs on a variety of 64-bit capable ARM hardware, from
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+embedded development boards to servers.
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Notes
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=====
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-1. Currenly, U-Boot run at the highest exception level processor
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- supported and jump to EL2 or optionally EL1 before enter OS.
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+1. U-Boot can run at any exception level it is entered in, it is
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+ recommened to enter it in EL3 if U-Boot takes some responsibilities of a
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+ classical firmware (like initial hardware setup, CPU errata workarounds
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+ or SMP bringup). U-Boot can be entered in EL2 when its main purpose is
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+ that of a boot loader. It can drop to lower exception levels before
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+ entering the OS.
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2. U-Boot for arm64 is compiled with AArch64-gcc. AArch64-gcc
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use rela relocation format, a tool(tools/relocate-rela) by Scott Wood
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is used to encode the initial addend of rela to u-boot.bin. After running,
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the U-Boot will be relocated to destination again.
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-3. Fdt should be placed at a 2-megabyte boundary and within the first 512
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- megabytes from the start of the kernel image. So, fdt_high should be
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- defined specially.
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+3. Earlier Linux kernel versions required the FDT to be placed at a
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+ 2 MB boundary and within the same 512 MB section as the kernel image,
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+ resulting in fdt_high to be defined specially.
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+ Since kernel version 4.2 Linux is more relaxed about the DT location, so it
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+ can be placed anywhere in memory.
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Please reference linux/Documentation/arm64/booting.txt for detail.
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4. Spin-table is used to wake up secondary processors. One location
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@@ -37,9 +45,8 @@ Notes
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aarch32 specific codes.
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-
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-Contributor
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-===========
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+Contributors
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+============
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Tom Rini <trini@ti.com>
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Scott Wood <scottwood@freescale.com>
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York Sun <yorksun@freescale.com>
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