Merge branch 'x86-efi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / x86 / boot.txt

diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index 473b32fd544e29a6bc1f3e9d357a4e13f3588597..9efceff51bfb1327a52e54af308a3077ccf7a02d 100644 (file)
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -54,6 +54,9 @@ Protocol 2.10:        (Kernel 2.6.31) Added a protocol for relaxed alignment
                beyond the kernel_alignment added, new init_size and
                pref_address fields.  Added extended boot loader IDs.
 
+Protocol 2.11: (Kernel 3.6) Added a field for offset of EFI handover
+               protocol entry point.
+
 **** MEMORY LAYOUT
 
 The traditional memory map for the kernel loader, used for Image or
@@ -189,6 +192,7 @@ Offset      Proto   Name            Meaning
                                of struct setup_data
 0258/8 2.10+   pref_address    Preferred loading address
 0260/4 2.10+   init_size       Linear memory required during initialization
+0264/4 2.11+   handover_offset Offset of handover entry point
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -693,6 +697,16 @@ Offset/size:       0x260/4
   else
        runtime_start = pref_address
 
+Field name:    handover_offset
+Type:          read
+Offset/size:   0x264/4
+
+  This field is the offset from the beginning of the kernel image to
+  the EFI handover protocol entry point. Boot loaders using the EFI
+  handover protocol to boot the kernel should jump to this offset.
+
+  See EFI HANDOVER PROTOCOL below for more details.
+
 
 **** THE IMAGE CHECKSUM
 
@@ -1013,3 +1027,30 @@ segment; __BOOS_CS must have execute/read permission, and __BOOT_DS
 must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
 must be __BOOT_DS; interrupt must be disabled; %esi must hold the base
 address of the struct boot_params; %ebp, %edi and %ebx must be zero.
+
+**** EFI HANDOVER PROTOCOL
+
+This protocol allows boot loaders to defer initialisation to the EFI
+boot stub. The boot loader is required to load the kernel/initrd(s)
+from the boot media and jump to the EFI handover protocol entry point
+which is hdr->handover_offset bytes from the beginning of
+startup_{32,64}.
+
+The function prototype for the handover entry point looks like this,
+
+    efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
+
+'handle' is the EFI image handle passed to the boot loader by the EFI
+firmware, 'table' is the EFI system table - these are the first two
+arguments of the "handoff state" as described in section 2.3 of the
+UEFI specification. 'bp' is the boot loader-allocated boot params.
+
+The boot loader *must* fill out the following fields in bp,
+
+    o hdr.code32_start
+    o hdr.cmd_line_ptr
+    o hdr.cmdline_size
+    o hdr.ramdisk_image (if applicable)
+    o hdr.ramdisk_size  (if applicable)
+
+All other fields should be zero.