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authorSimon Glass <sjg@chromium.org>2016-07-17 01:23:46 -0600
committerBin Meng <bmeng.cn@gmail.com>2016-08-16 11:44:09 +0800
commit37b4a9098c44f4dfc951c495bcc3439c2974b1db (patch)
tree228a0f55c1d6720b59e7b92ba889a36ab2b930bf
parent007adbc2f998258235bb1dc549becfcc22858e99 (diff)
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x86: Mention running U-Boot in 64-bit mode in the README
This feature is not supported. Document this, and add some details on how it might be implemented. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
-rw-r--r--doc/README.x8618
1 files changed, 18 insertions, 0 deletions
diff --git a/doc/README.x86 b/doc/README.x86
index 06b3de1..ba5bb99 100644
--- a/doc/README.x86
+++ b/doc/README.x86
@@ -1049,11 +1049,29 @@ provides the same EFI run-time services) is not currently supported on x86.
See README.efi for details of EFI support in U-Boot.
+64-bit Support
+--------------
+U-Boot supports booting a 64-bit kernel directly and is able to change to
+64-bit mode to do so. It also supports (with CONFIG_EFI_STUB) booting from
+both 32-bit and 64-bit UEFI. However, U-Boot itself is currently always built
+in 32-bit mode. Some access to the full memory range is provided with
+arch_phys_memset().
+
+The development work to make U-Boot itself run in 64-bit mode has not yet
+been attempted. The best approach would likely be to build a 32-bit SPL
+image for U-Boot, with CONFIG_SPL_BUILD. This could then handle the early CPU
+init in 16-bit and 32-bit mode, running the FSP and any other binaries that
+are needed. Then it could change to 64-bit model and jump to U-Boot proper.
+
+Given U-Boot's extensive 64-bit support this has not been a high priority,
+but it would be a nice addition.
+
TODO List
---------
- Audio
- Chrome OS verified boot
- Support for CONFIG_EFI_LOADER
+- Building U-Boot to run in 64-bit mode
References
----------