+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! >> >> 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 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. 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. Regards, Simon _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
