[PATCH 05/17] android: boot: add documentation for boot image header v3/v4 structure

[Safae Ouajih]

This was imported from [1], commit [2], file: include/bootimg/bootimg.h
[1] https://android.googlesource.com/platform/system/tools/mkbootimg
[2] cce5b1923e3cd2fcb765b512610bdc5c42bc501d

Signed-off-by: Safae Ouajih <souajih at baylibre.com>
---
 include/android_image.h | 136 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 135 insertions(+), 1 deletion(-)

diff --git a/include/android_image.h b/include/android_image.h
index ec36e6512ad6..62121e2a109b 100644
--- a/include/android_image.h
+++ b/include/android_image.h
@@ -3,7 +3,7 @@
  * This is from the Android Project,
  * Repository: https://android.googlesource.com/platform/system/tools/mkbootimg
  * File: include/bootimg/bootimg.h
- * Commit: e55998a0f2b61b685d5eb4a486ca3a0c680b1a2f
+ * Commit: cce5b1923e3cd2fcb765b512610bdc5c42bc501d
  *
  * Copyright (C) 2007 The Android Open Source Project
  */
@@ -183,4 +183,138 @@ struct andr_boot_img_hdr_v0_v1_v2 {
  *    else: jump to kernel_addr
  */
 
+/* When the boot image header has a version of 3, the structure of the boot
+ * image is as follows:
+ *
+ * +---------------------+
+ * | boot header         | 4096 bytes
+ * +---------------------+
+ * | kernel              | m pages
+ * +---------------------+
+ * | ramdisk             | n pages
+ * +---------------------+
+ *
+ * m = (kernel_size + 4096 - 1) / 4096
+ * n = (ramdisk_size + 4096 - 1) / 4096
+ *
+ * Note that in version 3 of the boot image header, page size is fixed at 4096 bytes.
+ *
+ * The structure of the vendor boot image (introduced with version 3 and
+ * required to be present when a v3 boot image is used) is as follows:
+ *
+ * +---------------------+
+ * | vendor boot header  | o pages
+ * +---------------------+
+ * | vendor ramdisk      | p pages
+ * +---------------------+
+ * | dtb                 | q pages
+ * +---------------------+
+ * o = (2112 + page_size - 1) / page_size
+ * p = (vendor_ramdisk_size + page_size - 1) / page_size
+ * q = (dtb_size + page_size - 1) / page_size
+ *
+ * 0. all entities in the boot image are 4096-byte aligned in flash, all
+ *    entities in the vendor boot image are page_size (determined by the vendor
+ *    and specified in the vendor boot image header) aligned in flash
+ * 1. kernel, ramdisk, vendor ramdisk, and DTB are required (size != 0)
+ * 2. load the kernel and DTB at the specified physical address (kernel_addr,
+ *    dtb_addr)
+ * 3. load the vendor ramdisk at ramdisk_addr
+ * 4. load the generic ramdisk immediately following the vendor ramdisk in
+ *    memory
+ * 5. set up registers for kernel entry as required by your architecture
+ * 6. if the platform has a second stage bootloader jump to it (must be
+ *    contained outside boot and vendor boot partitions), otherwise
+ *    jump to kernel_addr
+ */
+
+/* When the boot image header has a version of 4, the structure of the boot
+ * image is as follows:
+ *
+ * +---------------------+
+ * | boot header         | 4096 bytes
+ * +---------------------+
+ * | kernel              | m pages
+ * +---------------------+
+ * | ramdisk             | n pages
+ * +---------------------+
+ * | boot signature      | g pages
+ * +---------------------+
+ *
+ * m = (kernel_size + 4096 - 1) / 4096
+ * n = (ramdisk_size + 4096 - 1) / 4096
+ * g = (signature_size + 4096 - 1) / 4096
+ *
+ * Note that in version 4 of the boot image header, page size is fixed at 4096
+ * bytes.
+ *
+ * The structure of the vendor boot image version 4, which is required to be
+ * present when a version 4 boot image is used, is as follows:
+ *
+ * +------------------------+
+ * | vendor boot header     | o pages
+ * +------------------------+
+ * | vendor ramdisk section | p pages
+ * +------------------------+
+ * | dtb                    | q pages
+ * +------------------------+
+ * | vendor ramdisk table   | r pages
+ * +------------------------+
+ * | bootconfig             | s pages
+ * +------------------------+
+ *
+ * o = (2128 + page_size - 1) / page_size
+ * p = (vendor_ramdisk_size + page_size - 1) / page_size
+ * q = (dtb_size + page_size - 1) / page_size
+ * r = (vendor_ramdisk_table_size + page_size - 1) / page_size
+ * s = (vendor_bootconfig_size + page_size - 1) / page_size
+ *
+ * Note that in version 4 of the vendor boot image, multiple vendor ramdisks can
+ * be included in the vendor boot image. The bootloader can select a subset of
+ * ramdisks to load at runtime. To help the bootloader select the ramdisks, each
+ * ramdisk is tagged with a type tag and a set of hardware identifiers
+ * describing the board, soc or platform that this ramdisk is intended for.
+ *
+ * The vendor ramdisk section is consist of multiple ramdisk images concatenated
+ * one after another, and vendor_ramdisk_size is the size of the section, which
+ * is the total size of all the ramdisks included in the vendor boot image.
+ *
+ * The vendor ramdisk table holds the size, offset, type, name and hardware
+ * identifiers of each ramdisk. The type field denotes the type of its content.
+ * The vendor ramdisk names are unique. The hardware identifiers are specified
+ * in the board_id field in each table entry. The board_id field is consist of a
+ * vector of unsigned integer words, and the encoding scheme is defined by the
+ * hardware vendor.
+ *
+ * For the different type of ramdisks, there are:
+ *    - VENDOR_RAMDISK_TYPE_NONE indicates the value is unspecified.
+ *    - VENDOR_RAMDISK_TYPE_PLATFORM ramdisks contain platform specific bits, so
+ *      the bootloader should always load these into memory.
+ *    - VENDOR_RAMDISK_TYPE_RECOVERY ramdisks contain recovery resources, so
+ *      the bootloader should load these when booting into recovery.
+ *    - VENDOR_RAMDISK_TYPE_DLKM ramdisks contain dynamic loadable kernel
+ *      modules.
+ *
+ * Version 4 of the vendor boot image also adds a bootconfig section to the end
+ * of the image. This section contains Boot Configuration parameters known at
+ * build time. The bootloader is responsible for placing this section directly
+ * after the generic ramdisk, followed by the bootconfig trailer, before
+ * entering the kernel.
+ *
+ * 0. all entities in the boot image are 4096-byte aligned in flash, all
+ *    entities in the vendor boot image are page_size (determined by the vendor
+ *    and specified in the vendor boot image header) aligned in flash
+ * 1. kernel, ramdisk, and DTB are required (size != 0)
+ * 2. load the kernel and DTB at the specified physical address (kernel_addr,
+ *    dtb_addr)
+ * 3. load the vendor ramdisks at ramdisk_addr
+ * 4. load the generic ramdisk immediately following the vendor ramdisk in
+ *    memory
+ * 5. load the bootconfig immediately following the generic ramdisk. Add
+ *    additional bootconfig parameters followed by the bootconfig trailer.
+ * 6. set up registers for kernel entry as required by your architecture
+ * 7. if the platform has a second stage bootloader jump to it (must be
+ *    contained outside boot and vendor boot partitions), otherwise
+ *    jump to kernel_addr
+ */
 #endif
-- 
2.25.1