1 files changed, 114 insertions, 8 deletions

diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index e0203662f9e9..8da3a795083f 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -50,6 +50,10 @@ Protocol 2.08:	(Kernel 2.6.26) Added crc32 checksum and ELF format
 Protocol 2.09:  (Kernel 2.6.26) Added a field of 64-bit physical
                 pointer to single linked list of struct setup_data.
 
+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.
+
 **** MEMORY LAYOUT
 
 The traditional memory map for the kernel loader, used for Image or
@@ -168,12 +172,13 @@ Offset	Proto	Name		Meaning
 021C/4  2.00+   ramdisk_size    initrd size (set by boot loader)
 0220/4  2.00+   bootsect_kludge DO NOT USE - for bootsect.S use only
 0224/2  2.01+   heap_end_ptr    Free memory after setup end
-0226/2  N/A     pad1            Unused
+0226/1  2.02+(3 ext_loader_ver  Extended boot loader version
+0227/1  2.02+(3 ext_loader_type Extended boot loader ID
 0228/4  2.02+   cmd_line_ptr    32-bit pointer to the kernel command line
 022C/4  2.03+   ramdisk_max     Highest legal initrd address
 0230/4  2.05+   kernel_alignment Physical addr alignment required for kernel
 0234/1  2.05+   relocatable_kernel Whether kernel is relocatable or not
-0235/1  N/A     pad2            Unused
+0235/1  2.10+   min_alignment   Minimum alignment, as a power of two
 0236/2  N/A     pad3            Unused
 0238/4  2.06+   cmdline_size    Maximum size of the kernel command line
 023C/4  2.07+   hardware_subarch Hardware subarchitecture
@@ -182,6 +187,8 @@ Offset	Proto	Name		Meaning
 024C/4  2.08+   payload_length  Length of kernel payload
 0250/8  2.09+   setup_data      64-bit physical pointer to linked list
                                 of struct setup_data
+0258/8  2.10+   pref_address    Preferred loading address
+0260/4  2.10+   init_size       Linear memory required during initialization
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -190,6 +197,8 @@ Offset	Proto	Name		Meaning
     field are unusable, which means the size of a bzImage kernel
     cannot be determined.
 
+(3) Ignored, but safe to set, for boot protocols 2.02-2.09.
+
 If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
 the boot protocol version is "old".  Loading an old kernel, the
 following parameters should be assumed:
@@ -343,18 +352,32 @@ Protocol:	2.00+
   0xTV here, where T is an identifier for the boot loader and V is
   a version number.  Otherwise, enter 0xFF here.
 
+  For boot loader IDs above T = 0xD, write T = 0xE to this field and
+  write the extended ID minus 0x10 to the ext_loader_type field.
+  Similarly, the ext_loader_ver field can be used to provide more than
+  four bits for the bootloader version.
+
+  For example, for T = 0x15, V = 0x234, write:
+
+  type_of_loader  <- 0xE4
+  ext_loader_type <- 0x05
+  ext_loader_ver  <- 0x23
+
   Assigned boot loader ids:
         0  LILO                 (0x00 reserved for pre-2.00 bootloader)
         1  Loadlin
         2  bootsect-loader      (0x20, all other values reserved)
-        3  SYSLINUX
-        4  EtherBoot
+        3  Syslinux
+        4  Etherboot/gPXE
         5  ELILO
         7  GRUB
-        8  U-BOOT
+        8  U-Boot
         9  Xen
         A  Gujin
         B  Qemu
+        C  Arcturus Networks uCbootloader
+        E  Extended             (see ext_loader_type)
+        F  Special              (0xFF = undefined)
 
   Please contact <hpa@zytor.com> if you need a bootloader ID
   value assigned.
@@ -453,6 +476,35 @@ Protocol:	2.01+
   Set this field to the offset (from the beginning of the real-mode
   code) of the end of the setup stack/heap, minus 0x0200.
 
+Field name:     ext_loader_ver
+Type:           write (optional)
+Offset/size:    0x226/1
+Protocol:       2.02+
+
+  This field is used as an extension of the version number in the
+  type_of_loader field.  The total version number is considered to be
+  (type_of_loader & 0x0f) + (ext_loader_ver << 4).
+
+  The use of this field is boot loader specific.  If not written, it
+  is zero.
+
+  Kernels prior to 2.6.31 did not recognize this field, but it is safe
+  to write for protocol version 2.02 or higher.
+
+Field name:     ext_loader_type
+Type:           write (obligatory if (type_of_loader & 0xf0) == 0xe0)
+Offset/size:    0x227/1
+Protocol:       2.02+
+
+  This field is used as an extension of the type number in
+  type_of_loader field.  If the type in type_of_loader is 0xE, then
+  the actual type is (ext_loader_type + 0x10).
+
+  This field is ignored if the type in type_of_loader is not 0xE.
+
+  Kernels prior to 2.6.31 did not recognize this field, but it is safe
+  to write for protocol version 2.02 or higher.
+
 Field name:     cmd_line_ptr
 Type:           write (obligatory)
 Offset/size:    0x228/4
@@ -482,11 +534,19 @@ Protocol:	2.03+
   0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
 
 Field name:     kernel_alignment
-Type:           read (reloc)
+Type:           read/modify (reloc)
 Offset/size:    0x230/4
-Protocol:       2.05+
+Protocol:       2.05+ (read), 2.10+ (modify)
+
+  Alignment unit required by the kernel (if relocatable_kernel is
+  true.)  A relocatable kernel that is loaded at an alignment
+  incompatible with the value in this field will be realigned during
+  kernel initialization.
 
-  Alignment unit required by the kernel (if relocatable_kernel is true.)
+  Starting with protocol version 2.10, this reflects the kernel
+  alignment preferred for optimal performance; it is possible for the
+  loader to modify this field to permit a lesser alignment.  See the
+  min_alignment and pref_address field below.
 
 Field name:     relocatable_kernel
 Type:           read (reloc)
@@ -498,6 +558,22 @@ Protocol:	2.05+
   After loading, the boot loader must set the code32_start field to
   point to the loaded code, or to a boot loader hook.
 
+Field name:     min_alignment
+Type:           read (reloc)
+Offset/size:    0x235/1
+Protocol:       2.10+
+
+  This field, if nonzero, indicates as a power of two the minimum
+  alignment required, as opposed to preferred, by the kernel to boot.
+  If a boot loader makes use of this field, it should update the
+  kernel_alignment field with the alignment unit desired; typically:
+
+        kernel_alignment = 1 << min_alignment
+
+  There may be a considerable performance cost with an excessively
+  misaligned kernel.  Therefore, a loader should typically try each
+  power-of-two alignment from kernel_alignment down to this alignment.
+
 Field name:     cmdline_size
 Type:           read
 Offset/size:    0x238/4
@@ -582,6 +658,36 @@ Protocol:	2.09+
   sure to consider the case where the linked list already contains
   entries.
 
+Field name:     pref_address
+Type:           read (reloc)
+Offset/size:    0x258/8
+Protocol:       2.10+
+
+  This field, if nonzero, represents a preferred load address for the
+  kernel.  A relocating bootloader should attempt to load at this
+  address if possible.
+
+  A non-relocatable kernel will unconditionally move itself and to run
+  at this address.
+
+Field name:     init_size
+Type:           read
+Offset/size:    0x25c/4
+
+  This field indicates the amount of linear contiguous memory starting
+  at the kernel runtime start address that the kernel needs before it
+  is capable of examining its memory map.  This is not the same thing
+  as the total amount of memory the kernel needs to boot, but it can
+  be used by a relocating boot loader to help select a safe load
+  address for the kernel.
+
+  The kernel runtime start address is determined by the following algorithm:
+
+  if (relocatable_kernel)
+        runtime_start = align_up(load_address, kernel_alignment)
+  else
+        runtime_start = pref_address
+
 
 **** THE IMAGE CHECKSUM