Hi Simon,
On Mon, Sep 26, 2016 at 11:33 AM, Simon Glass sjg@chromium.org wrote:
At present U-Boot runs entirely in 32-bit mode on x86, except for the initial switch from 16-bit mode. On 64-bit machines it is possible to run in 64-bit mode. This series starts the process of adding this support.
The main benefit of 64-bit mode for a boot loader is direct access to all available memory. There are also more registers, but this makes very little difference.
This feature is implemented by putting all of the 32-bit code in an SPL build. SPL then runs through all the init that has to be done in 32-bit mode, changes to 64-bit mode and then jumps to U-Boot proper.
Typically the total code size increases slightly. For example, on link in 32-bit mode, U-Boot has around 480KB of code (admittedly with a large number of features enabled). In 64-bit mode, U-Boot falls to around 460KB, but SPL adds another 60KB, for a net increase of 40KB. Partly this is due to code duplication and partly it is due to the worse code density of 64-bit code on x86.
Many major features are not implemented yet, for example:
- SDRAM sizing
- Booting linux
- FSP support
- EFI support
- SCSI device init
- Running video ROMs
Still, this is a big step forward towards full 64-bit support. To enable it, select CONFIG_X86_RUN_64BIT.
This series is available at u-boot-x86/64-working
Looks it requires a 64-bit toolchain to compile 64-bit U-Boot. For example, I used kernel.org i386 toolchain to compile 64-bit U-Boot, I got:
include/asm-generic/bitops/__fls.h: In function '__fls': include/asm-generic/bitops/__fls.h:17:2: warning: left shift count >= width of type if (!(word & (~0ul << 32))) { ^ include/asm-generic/bitops/__fls.h:19:3: warning: left shift count >= width of type word <<= 32; ^ include/asm-generic/bitops/__fls.h:22:2: warning: left shift count >= width of type if (!(word & (~0ul << (BITS_PER_LONG-16)))) { ^ include/asm-generic/bitops/__fls.h:26:2: warning: left shift count >= width of type if (!(word & (~0ul << (BITS_PER_LONG-8)))) { ^ include/asm-generic/bitops/__fls.h:30:2: warning: left shift count >= width of type if (!(word & (~0ul << (BITS_PER_LONG-4)))) { ^ include/asm-generic/bitops/__fls.h:34:2: warning: left shift count >= width of type if (!(word & (~0ul << (BITS_PER_LONG-2)))) { ^ include/asm-generic/bitops/__fls.h:38:2: warning: left shift count >= width of type if (!(word & (~0ul << (BITS_PER_LONG-1)))) ^ arch/x86/cpu/intel_common/microcode.c: In function 'microcode_read_rev': arch/x86/cpu/intel_common/microcode.c:79:2: error: PIC register clobbered by 'ebx' in 'asm' asm volatile ( ^ make[2]: *** [arch/x86/cpu/intel_common/microcode.o] Error 1
After I switched to 64-bit toolchain from kernel.org (x86_64-linux), there was no such warnings/errors, but I still got build failure at last.
./tools/binman/binman -d u-boot.dtb -O . -I . -I ./board/google/chromebook_link u-boot-x86-16bit.bin Traceback (most recent call last): File "./tools/binman/binman", line 31, in <module> import control File "./tools/binman/control.py", line 17, in <module> from image import Image File "./tools/binman/image.py", line 12, in <module> import entry File "./tools/binman/etype/entry.py", line 8, in <module> import importlib ImportError: No module named importlib make: *** [u-boot.rom] Error 1
Regards, Bin