Hi Simon, On Tue, Feb 2, 2016 at 11:58 AM, Simon Glass <[email protected]> wrote: > +Bin (sorry, meant to copy you before) > > Hi Albert, > > On 1 February 2016 at 00:14, Albert ARIBAUD <[email protected]> wrote: >> Hello Simon, >> >> On Sun, 31 Jan 2016 19:20:31 -0700, Simon Glass <[email protected]> >> wrote: >>> Hi Bin, >>> >>> At present U-Boot supports booting a 64-bit kernel directly. It can >>> also be loaded as a 64-bit payload from EFI. But it cannot be built as >>> a 64-bit boot loader. >>> >>> I took a bit of a look at this. It looks like we need to stay in >>> 32-bit mode until the FSP is loaded. Also, to get to 64-bit mode I'm >>> pretty sure we need page tables, which means we need somewhere to put >>> them! >>>
Yes unfortunately that is the FSP limitation. >>> Looking at the board_f init sequence, it seems that arch_cpu_init() is >>> the earlist we could switch to 64-bit. We'd need to grab some memory >>> from somewhere to do this - I wonder if this can be CAR? There is no >>> SRAM on x86 chips I think. >>> >>> For non-FSP devices we don't init the RAM until much later - >>> dram_init(). That means that a significant portion of the init >>> sequence would be 32-bit code. I'm not sure that will work. >>> I believe we can do dram_init() in 64-bit mode as well if MRC is written in pure C. >>> I suppose one option is to only go to 64-bit mode when relocating. But >>> then we end up with lots of code that needs to run in 32-bit and >>> 64-bit. >>> >>> Do you have any ideas on this? >> >> How about starting with implementing the last option, i.e. switch to 64 >> bits when DDR is available, mainline that, then progressively work your >> way toward an earlier switch? > > The tricky thing is that I'm not sure we can run 32-bit code in 64-bit > mode or vice-versa. The instruction set is similar but there are data > size settings that probably make it incompatible. > No, it's not 100% compatible. We have to switch back and forth unfortunately. > I wonder whether we might need to resort to SPL for the 32-bit > portion, and jump to a 64-bit U-Boot from there? Tegra does something > similar to that. > What's the benefit of doing a 64-bit bootloader? Intel's UEFI BIOS has a 32-bit and 64-bit version, and has caused some troubles for the next stage loader (bootia32.efi vs. bootx64.efi). I know for PowerPC, a 64-bit U-Boot does not exist as 32-bit U-Boot can load 32-bit and 64-bit kernel, just like what we have for x86. 64-bit U-Boot was only seen on ARMv8, but that's the architecture limitation I believe, and we have to do that. Regards, Bin _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
