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+# U-boot
+U-boot is a bootloader, not a firmware standard like UEFI.
+
+## U-boot boot methods
+### U-Boot's own boot protocol
+- Loads a flat binary or uImage
+- Passes device tree in X0 (or R2 on 32-bit)
+- No UEFI involved at all
+
+### U-Boot as UEFI firmware
+- U-boot builded with CONFIG_EFI_LOADER
+- Loads and runs 3efi PE32+ applications
+- Bastion kernel should work perfectly
+
+### booti/bootm commands
+- Loads Linux-format Image with header
+- Passes device tree pointer
+
+### Modify u-boot to run bastion kernel
+Worst case
+
+## Easiest method
+is using u-boot as uefi loader
+For it i need to build u-boot with CONFIG_EFI_LOADER.
+U-boot provides the same EFI_SYSTEM_TABLE, EFI_BOOT_SERVICES, GOP, memory map and ExitBootServices() that real UEFI firmware does.
+A lot of ARM Linux platforms use it - they run GRUB(grubaa64.efi) from u-boot and then run kernel.
+
+## Not-easiest method
+Use u-boot's own boot proto
+Here's how it works:
+- The kernel is loaded as a flat bin (or a uImage wrapper)
+- CPU is en EL2 or EL1, MMU off, caches off
+- X0 = physical address of the device tree blof (FDT)
+- No memory map - we need to parse dt's /memory node
+- No framebuffer setup - we need to configure it from dt
+- No ExitBootServices - u-boot is already gone when we get control
+
+### Kernel image format
+U-boot expects same as Linux's Image format - a flat binary with 64-byte header:
+```
+// ARM64 Image header (at offset 0 of the binary)
+struct arm64_image_header {
+    uint32_t code0;          // Executable code (branch instruction)
+    uint32_t code1;          // Executable code
+    uint64_t text_offset;    // Image load offset from start of RAM
+    uint64_t image_size;     // Effective image size (0 = unknown)
+    uint64_t flags;          // Kernel flags
+    uint64_t res2;           // Reserved
+    uint64_t res3;           // Reserved
+    uint64_t res4;           // Reserved
+    uint32_t magic;          // Magic: 0x644D5241 ("ARM\x64")
+    uint32_t res5;           // Reserved (used for PE offset if EFI stub)
+};
+```
+
+# Current state
+Bastion kernel supports only UEFI boot loading and not support own u-boot protos