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Coreboot is a first-stage bootloader mostly used on x86 devices as an alternative to UEFI. Coreboot runs in 32-bit mode. U-Boot currently supports booting from coreboot as a second-stage bootloader, also in 32-bit mode. However it is useful to be able to run U-Boot in 64-bit mode. To do this we can have a 32-bit SPL which switches over the CPU and jumps to a 64-bit U-Boot proper. Add a new 'coreboot64' board for running 64-bit U-Boot from coreboot. This uses binman to create an image with a 32-bit SPL and a 64-bit U-Boot. This allows running 64-bit EFI images on x86, for example, without needing a native U-Boot port for a board. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Tested-by: Bin Meng <bmeng.cn@gmail.com>
53 lines
2.0 KiB
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53 lines
2.0 KiB
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.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Bin Meng <bmeng.cn@gmail.com>
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Coreboot
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========
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Build Instructions for U-Boot as coreboot payload
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-------------------------------------------------
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Building U-Boot as a coreboot payload is just like building U-Boot for targets
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on other architectures, like below::
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$ make coreboot_defconfig
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$ make all
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Test with coreboot
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------------------
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For testing U-Boot as the coreboot payload, there are things that need be paid
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attention to. coreboot supports loading an ELF executable and a 32-bit plain
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binary, as well as other supported payloads. With the default configuration,
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U-Boot is set up to use a separate Device Tree Blob (dtb). As of today, the
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generated u-boot-dtb.bin needs to be packaged by the cbfstool utility (a tool
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provided by coreboot) manually as coreboot's 'make menuconfig' does not provide
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this capability yet. The command is as follows::
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# in the coreboot root directory
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$ ./build/util/cbfstool/cbfstool build/coreboot.rom add-flat-binary \
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-f u-boot-dtb.bin -n fallback/payload -c lzma -l 0x1110000 -e 0x1110000
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Make sure 0x1110000 matches CONFIG_SYS_TEXT_BASE, which is the symbol address
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of _x86boot_start (in arch/x86/cpu/start.S).
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If you want to use ELF as the coreboot payload, change U-Boot configuration to
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use CONFIG_OF_EMBED instead of CONFIG_OF_SEPARATE.
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To enable video you must enable these options in coreboot:
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- Set framebuffer graphics resolution (1280x1024 32k-color (1:5:5))
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- Keep VESA framebuffer
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At present it seems that for Minnowboard Max, coreboot does not pass through
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the video information correctly (it always says the resolution is 0x0). This
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works correctly for link though.
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64-bit U-Boot
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-------------
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In addition to the 32-bit 'coreboot' build there is a 'coreboot64' build. This
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produces an image which can be booted from coreboot (32-bit). Internally it
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works by using a 32-bit SPL binary to switch to 64-bit for running U-Boot. It
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can be useful for running UEFI applications, for example.
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This has only been lightly tested.
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