X-Git-Url: https://git.sur5r.net/?a=blobdiff_plain;f=doc%2FREADME.arm64;h=b0bba0fc65e4634c602fdab7627e0d7b4ba4758f;hb=6c88079e24816567dbb234fcfb52419661338d1f;hp=75586dbaa703779e055e042c093837693658b8f0;hpb=0ae7653128c80a4f2920cbe9b124792c2fd9d9e0;p=u-boot diff --git a/doc/README.arm64 b/doc/README.arm64 index 75586dbaa7..b0bba0fc65 100644 --- 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 @@ -36,11 +44,13 @@ Notes 6. CONFIG_ARM64 instead of CONFIG_ARMV8 is used to distinguish aarch64 and aarch32 specific codes. -Contributor -=========== - Tom Rini - Scott Wood - York Sun - Simon Glass - Sharma Bhupesh - Rob Herring + +Contributors +============ + Tom Rini + Scott Wood + York Sun + Simon Glass + Sharma Bhupesh + Rob Herring + Sergey Temerkhanov