| U-Boot for arm64 | |
| Summary | |
| ======= | |
| 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. 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. 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 | |
| (or per processor location) is defined to hold the kernel entry point | |
| for secondary processors. It must be ensured that the location is | |
| accessible and zero immediately after secondary processor | |
| enter slave_cpu branch execution in start.S. The location address | |
| is encoded in cpu node of DTS. Linux kernel store the entry point | |
| of secondary processors to it and send event to wakeup secondary | |
| processors. | |
| Please reference linux/Documentation/arm64/booting.txt for detail. | |
| 5. Generic board is supported. | |
| 6. CONFIG_ARM64 instead of CONFIG_ARMV8 is used to distinguish aarch64 and | |
| aarch32 specific codes. | |
| Contributors | |
| ============ | |
| Tom Rini <trini@ti.com> | |
| Scott Wood <scottwood@freescale.com> | |
| York Sun <yorksun@freescale.com> | |
| Simon Glass <sjg@chromium.org> | |
| Sharma Bhupesh <bhupesh.sharma@freescale.com> | |
| Rob Herring <robherring2@gmail.com> | |
| Sergey Temerkhanov <s.temerkhanov@gmail.com> |