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Refer to device/*/dtbtool.txt
---------------------------------------------------------------------
Copyright (c) 2012, The Linux Foundation. All rights reserved.
Redistribution and use in source form and compiled forms (SGML, HTML,
PDF, PostScript, RTF and so forth) with or without modification, are
permitted provided that the following conditions are met:
Redistributions in source form must retain the above copyright
notice, this list of conditions and the following disclaimer as the
first lines of this file unmodified.
Redistributions in compiled form (transformed to other DTDs,
converted to PDF, PostScript, RTF and other formats) must reproduce
the above copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials provided with
the distribution.
THIS DOCUMENTATION IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE AND
NON-INFRINGEMENT ARE DISCLAIMED. IN NO EVENT SHALL THE FREEBSD
DOCUMENTATION PROJECT BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS DOCUMENTATION, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
DAMAGE.
Android - Table of Device Tree
==============================
0) Document revision
v1.0 - Initial version (dng)
1) Android boot image:
----------------------
1.1) Header:
1) Magic (8B)
2) kernel size (4B)
3) kernel addr (4B)
4) ramdisk size (4B)
5) ramdisk addr (4B)
6) 2ndary size (4B)
7) 2ndary addr (4B)
8) tags addr (4B)
9) page size (4B)
10) unused #1 (4B) (zero in standard Android)
11) unused #2 (4B) (zero in standard Android)
12) product name (16B)
13) kernel cmdline (512B)
14) id (8B)
1.2) Layout:
A) header (as above - 1 page)
B) kernel (n pages)
C) ramdisk (m pages)
D) second stage (o pages)
2) QC table of device tree
--------------------------
2.1) Changes:
i) use "unused #1, #2" members in existing boot image
header to point to new table of device tree
(#1 - size of QC table of DT)
ii) append table of device tree (described later)
after "D) second stage"
2.2) Format:
size
x +------------------+
| | MAGIC ("QCDT") | 4B
| +------------------+
header | VERSION | uint32 (initial version 1)
| +------------------+
| | num of DTBs | uint32 (number of DTB entries)
x +------------------+
| | platform id #1 | uint32 (e.g. ID for MSM8974)
| +------------------+
| | variant id #1 | uint32 (e.g. ID for CDP, MTP)
device +------------------+
#1 | soc rev #1 | uint32 (e.g. MSM8974 v2)
entry +------------------+
| | offset #1 | uint32 (byte offset from start/before MAGIC
| +------------------+ to DTB entry)
| | size #1 | uint32 (size in bytes of DTB blob)
x +------------------+
. .
. . (repeat)
. .
x +------------------+
| | platform id #Z | uint32 (e.g. ID for MSM8974)
| +------------------+
device | variant id #Z | uint32 (e.g. ID for CDP, MTP)
#Z +------------------+
entry | soc rev #Z | uint32 (e.g. MSM8974 v2)
(last) +------------------+
| | offset #Z | uint32 (byte offset from start/before MAGIC
x +------------------+ to DTB entry)
| 0 ("zero") | uint32 (end of list delimiter)
+------------------+ to DTB entry)
| padding | variable length for next DTB to start on
+------------------+ page boundary
| DTB #1 | variable (start is page aligned)
| |
| |
+------------------+
| padding | variable length for next DTB to start on
+------------------+ page boundary
.
.
.
+------------------+
| DTB #Z (last) | variable (start is page aligned)
| |
| |
+------------------+
3) Operations
-------------
3.1) Build-time:
1) Each DTS per device will add a "qcom,msm-id" triplet
e.g. for msm8974-sim.dts, add
qcom,msm-id = <x y z>;
x = ID for msm8974
y = ID for CDP, MTP, etc.
z = ID for soc revision
The triplet can optionally be an array of triplets:
qcom,msm-id = <x1, y1, z1>, <x2, y2, z2>, ...;
2) Kernel compile will generate the DTB
3) Android build will run a new tool (dtbTool)
a) scan the DTB output directory for all compiled DTB
b) decompile the DTB for "qcom,msm-id"
c) generate the QC table of device tree in sorted
order (platform, variant, soc rev)
d) modified mkbootimg will merge new table of DT
3.2) Run-time:
1) LK bootloader will obtain MSM id/variant/soc rev info
either from early bootloaders or via other means
2) LK bootloader will check entries #10 for non-zero
value (set to zero for standard boot.img). If the
value is non-zero, refer to page section after
the "second stage" in the boot.img layout
3) Check QCDT magic
4) Check QCDT version (optional LK to handle multiple
QCDT version)
5) LK scans through the QCDT table to look for matching
entry. Search order is:
1) platform ID exact match
2) variant ID exact match
3) select the highest soc rev in QCDT that is
equal to or lower than the runtime detected soc rev
6) Load the matching DTB blob to the tags addr
7) LK pass the correct DTB to the kernel