1*4882a593SmuzhiyunU-Boot for arm64 2*4882a593Smuzhiyun 3*4882a593SmuzhiyunSummary 4*4882a593Smuzhiyun======= 5*4882a593SmuzhiyunThe initial arm64 U-Boot port was developed before hardware was available, 6*4882a593Smuzhiyunso the first supported platforms were the Foundation and Fast Model for ARMv8. 7*4882a593SmuzhiyunThese days U-Boot runs on a variety of 64-bit capable ARM hardware, from 8*4882a593Smuzhiyunembedded development boards to servers. 9*4882a593Smuzhiyun 10*4882a593SmuzhiyunNotes 11*4882a593Smuzhiyun===== 12*4882a593Smuzhiyun 13*4882a593Smuzhiyun1. U-Boot can run at any exception level it is entered in, it is 14*4882a593Smuzhiyun recommened to enter it in EL3 if U-Boot takes some responsibilities of a 15*4882a593Smuzhiyun classical firmware (like initial hardware setup, CPU errata workarounds 16*4882a593Smuzhiyun or SMP bringup). U-Boot can be entered in EL2 when its main purpose is 17*4882a593Smuzhiyun that of a boot loader. It can drop to lower exception levels before 18*4882a593Smuzhiyun entering the OS. 19*4882a593Smuzhiyun 20*4882a593Smuzhiyun2. U-Boot for arm64 is compiled with AArch64-gcc. AArch64-gcc 21*4882a593Smuzhiyun use rela relocation format, a tool(tools/relocate-rela) by Scott Wood 22*4882a593Smuzhiyun is used to encode the initial addend of rela to u-boot.bin. After running, 23*4882a593Smuzhiyun the U-Boot will be relocated to destination again. 24*4882a593Smuzhiyun 25*4882a593Smuzhiyun3. Earlier Linux kernel versions required the FDT to be placed at a 26*4882a593Smuzhiyun 2 MB boundary and within the same 512 MB section as the kernel image, 27*4882a593Smuzhiyun resulting in fdt_high to be defined specially. 28*4882a593Smuzhiyun Since kernel version 4.2 Linux is more relaxed about the DT location, so it 29*4882a593Smuzhiyun can be placed anywhere in memory. 30*4882a593Smuzhiyun Please reference linux/Documentation/arm64/booting.txt for detail. 31*4882a593Smuzhiyun 32*4882a593Smuzhiyun4. Spin-table is used to wake up secondary processors. One location 33*4882a593Smuzhiyun (or per processor location) is defined to hold the kernel entry point 34*4882a593Smuzhiyun for secondary processors. It must be ensured that the location is 35*4882a593Smuzhiyun accessible and zero immediately after secondary processor 36*4882a593Smuzhiyun enter slave_cpu branch execution in start.S. The location address 37*4882a593Smuzhiyun is encoded in cpu node of DTS. Linux kernel store the entry point 38*4882a593Smuzhiyun of secondary processors to it and send event to wakeup secondary 39*4882a593Smuzhiyun processors. 40*4882a593Smuzhiyun Please reference linux/Documentation/arm64/booting.txt for detail. 41*4882a593Smuzhiyun 42*4882a593Smuzhiyun5. Generic board is supported. 43*4882a593Smuzhiyun 44*4882a593Smuzhiyun6. CONFIG_ARM64 instead of CONFIG_ARMV8 is used to distinguish aarch64 and 45*4882a593Smuzhiyun aarch32 specific codes. 46*4882a593Smuzhiyun 47*4882a593Smuzhiyun 48*4882a593SmuzhiyunContributors 49*4882a593Smuzhiyun============ 50*4882a593Smuzhiyun Tom Rini <trini@ti.com> 51*4882a593Smuzhiyun Scott Wood <scottwood@freescale.com> 52*4882a593Smuzhiyun York Sun <yorksun@freescale.com> 53*4882a593Smuzhiyun Simon Glass <sjg@chromium.org> 54*4882a593Smuzhiyun Sharma Bhupesh <bhupesh.sharma@freescale.com> 55*4882a593Smuzhiyun Rob Herring <robherring2@gmail.com> 56*4882a593Smuzhiyun Sergey Temerkhanov <s.temerkhanov@gmail.com> 57