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PiperOrigin-RevId: 207940242
Change-Id: I3dee204c744e2e6062ac56810b88aefabf84636a

1 files changed, 171 insertions, 90 deletions

diff --git a/en/devices/architecture/dto/optimize.html b/en/devices/architecture/dto/optimize.html
index 7502d7ad..7624cc14 100644
--- a/en/devices/architecture/dto/optimize.html
+++ b/en/devices/architecture/dto/optimize.html
@@ -5,6 +5,7 @@
     <meta name="book_path" value="/_book.yaml" />
   </head>
   <body>
+  {% include "_versions.html" %}
   <!--
       Copyright 2017 The Android Open Source Project
 
@@ -21,14 +22,21 @@
       limitations under the License.
   -->
 
-<p>This page details optimizations you can make to your DTO implementation,
-describes restrictions against overlaying the root node, and provides sample
-implementation instructions and code.</p>
+<p>
+  This page discusses optimizations you can make to your DTO implementation,
+  describes restrictions against overlaying the root node, and details how to
+  configure compressed overlays in the DTBO image. It also provides sample
+  implementation instructions and code.
+</p>
 
 <h2 id=kernel>Kernel command line</h2>
-<p>The original kernel command line in device tree is located in the
-<code>chosen/bootargs</code> node. The bootloader must concatenate this location
-with other sources of kernel command line:</p>
+
+<p>
+  The original kernel command line in device tree is located in the
+  <code>chosen/bootargs</code> node. The bootloader must concatenate this
+  location with other sources of kernel command line:
+</p>
+
 <pre class="prettyprint">
 /dts-v1/;
 
@@ -39,11 +47,13 @@ with other sources of kernel command line:</p>
 };
 </pre>
 
-<p>DTO <strong>cannot</strong> concatenate values from main DT and overlay DT.
-We recommend putting the kernel command line of the main DT in
-<code>chosen/bootargs</code> and the kernel command line of the overlay DT in
-<code>chosen/bootargs_ext</code>. Bootloader can then concatenate these
-locations and pass the result to the kernel.</p>
+<p>
+  DTO <strong>cannot</strong> concatenate values from main DT and overlay DT, so
+  you must put the kernel command line of the main DT in
+  <code>chosen/bootargs</code> and the kernel command line of the overlay DT in
+  <code>chosen/bootargs_ext</code>. Bootloader can then concatenate these
+  locations and pass the result to the kernel.
+</p>
 
 <table>
 <tr>
@@ -77,47 +87,70 @@ locations and pass the result to the kernel.</p>
 </table>
 
 <h2 id=libufdt>libufdt</h2>
-<p>While the latest
-<code><a href="https://github.com/dgibson/dtc/tree/master/libfdt" class="external">libfdt</code></a>
-supports DTO, we recommend using <code>libufdt</code> to implement DTO (source
-at
-<code><a href="https://android.googlesource.com/platform/system/libufdt/+/refs/heads/master" class="external">platform/system/libufdt</code></a>
-in AOSP). <code>libufdt</code> builds a real tree structure (un-flattened device
-tree, or <em>ufdt</em>) from the flattened device tree (FDT), so it can improve
-the merging of two <code>.dtb</code> files from O(N2) to O(N), where N is the
-number of nodes in the tree.</p>
+
+<p>
+  While the latest
+  <code><a href="https://github.com/dgibson/dtc/tree/master/libfdt" class="external">libfdt</code></a>
+  supports DTO, is it recommended to use <code>libufdt</code> to implement DTO
+  (AOSP source at
+  <code><a href="https://android.googlesource.com/platform/system/libufdt/+/refs/heads/master" class="external">platform/system/libufdt</code></a>).
+  <code>libufdt</code> builds a real tree structure (un-flattened device tree,
+  or <em>ufdt</em>) from the flattened device tree (FDT), so it can improve the
+  merging of two <code>.dtb</code> files from O(N2) to O(N), where N is the
+  number of nodes in the tree.
+</p>
 
 <h3 id=performance>Performance testing</h3>
-<p>In Google's internal testing, using <code>libufdt</code> on 2405
-<code>.dtb</code> and 283 <code>.dtbo</code> DT nodes results in file sizes of
-70,618 and 8,566 bytes after compilation. Compared with a
-<a href="http://fxr.watson.org/fxr/source/boot/fdt/" class="external">DTO
-implementation</a> ported from FreeBSD (124ms runtime), <code>libufdt</code>
-DTO runtime is 10ms.</p>
-
-<p>In performance testing for Pixel devices, we compared <code>libufdt</code>
-and <code>libfdt</code>. The number of base nodes effect is similar, but
-includes the following differences:</p>
+
+<p>
+  In Google's internal testing, using <code>libufdt</code> on 2405
+  <code>.dtb</code> and 283 <code>.dtbo</code> DT nodes results in file sizes of
+  70,618 and 8,566 bytes after compilation. Compared with a
+  <a href="http://fxr.watson.org/fxr/source/boot/fdt/" class="external">DTO
+  implementation</a> ported from FreeBSD (124 ms runtime), <code>libufdt</code>
+  DTO runtime is 10 ms.
+</p>
+
+<p>
+  Performance testing for Pixel devices compared <code>libufdt</code> and
+  <code>libfdt</code>. The number of base nodes effect is similar, but includes
+  the following differences:
+</p>
+
 <ul>
-<li>500 overlay (append or override) operations have 6~8x time difference</li>
-<li>1000 overlay (append or override) operations have 8~10x time difference</li>
+  <li>500 overlay (append or override) operations have 6x to 8x time
+  difference</li>
+  <li>1000 overlay (append or override) operations have 8x to 10x time
+  difference</li>
 </ul>
 
-<p>Example with appending count set to X:</p>
+<p>
+  Example with appending count set to X:
+</p>
+
 <p><img src="../images/treble_dto_appending.png"></p>
-<figcaption><strong>Figure 1.</strong> Appending count is X.</figcaption>
+<figcaption><strong>Figure 1.</strong> Appending count is X</figcaption>
+
+<p>
+  Example with overriding count set to X:
+</p>
 
-<p>Example with overriding count set to X:</p>
 <p><img src="../images/treble_dto_overriding.png"></p>
-<figcaption><strong>Figure 2.</strong> Overriding count is X.</figcaption>
+<figcaption><strong>Figure 2.</strong> Overriding count is X</figcaption>
 
-<p><code>libufdt</code> is developed with some <code>libfdt</code> APIs and data
-structures. When using <code>libufdt</code>, you must include and link
-<code>libfdt</code> (however in your code you can use <code>libfdt</code> API to
-operate DTB or DTBO).</p>
+<p>
+  <code>libufdt</code> is developed with some <code>libfdt</code> APIs and data
+  structures. When using <code>libufdt</code>, you must include and link
+  <code>libfdt</code> (however, in your code you can use the <code>libfdt</code>
+  API to operate DTB or DTBO).
+</p>
 
 <h3 id=api>libufdt DTO API</h3>
-<p>The main API to DTO in <code>libufdt</code> is as follows:</p>
+
+<p>
+  The main API to DTO in <code>libufdt</code> is as follows:
+</p>
+
 <pre class="prettyprint">
 struct fdt_header *ufdt_apply_overlay(
         struct fdt_header *main_fdt_header,
@@ -126,30 +159,39 @@ struct fdt_header *ufdt_apply_overlay(
         size_t overlay_size);
 </pre>
 
-<p>The parameter <code>main_fdt_header</code> is the main DT and
-<code>overlay_fdt</code> is the buffer containing the contents of a
-<code>.dtbo</code> file. The return value is a new buffer containing the merged
-DT (or <code>null</code> in case of error). The merged DT is formated in FDT,
-which you can pass to the kernel when starting the kernel.</p>
-
-<p>The new buffer from the return value is created by <code>dto_malloc()</code>,
-which you should implement when porting <code>libufdt</code> into bootloader.
-For reference implementations, refer to
-<code>sysdeps/libufdt_sysdeps_*.c</code>.</p>
+<p>
+  The parameter <code>main_fdt_header</code> is the main DT and
+  <code>overlay_fdt</code> is the buffer containing the contents of a
+  <code>.dtbo</code> file. The return value is a new buffer containing the
+  merged DT (or <code>null</code> in case of error). The merged DT is formated
+  in FDT, which you can pass to the kernel when starting the kernel.
+</p>
+
+<p>
+  The new buffer from the return value is created by <code>dto_malloc()</code>,
+  which you should implement when porting <code>libufdt</code> into bootloader.
+  For reference implementations, refer to
+  <code>sysdeps/libufdt_sysdeps_*.c</code>.
+</p>
 
 <h2 id=root>Root node restrictions</h2>
-<p>You cannot overlay a new node or property into the root node of main DT
-because overlay operations rely on labels. Because the main DT must define a
-label and the overlay DT assigns the nodes to be overlaid with labels, we
-cannot give a label for the root node (and therefore cannot overlay the root
-node).</p>
-
-<p>SoC vendors must define the overlaying ability of main DT; ODM/OEMs can only
-append or override nodes with labels defined by the SoC vendor. As a workaround,
-you can define a <strong><code>odm</code></strong> node under the root node in
-base DT, enabling all ODM nodes in overlay DT to add new nodes. Alternatively,
-you could put all SoC-related nodes in the base DT into a
-<strong><code>soc</code></strong> node under root node as described below:</p>
+
+<p>
+  You cannot overlay a new node or property into the root node of main DT
+  because overlay operations rely on labels. Because the main DT must define a
+  label and the overlay DT assigns the nodes to be overlaid with labels, you
+  cannot give a label for the root node (and therefore cannot overlay the root
+  node).
+</p>
+
+<p>
+  SoC vendors must define the overlaying ability of main DT; ODM/OEMs can only
+  append or override nodes with labels defined by the SoC vendor. As a
+  workaround, you can define an <strong><code>odm</code></strong> node under the
+  root node in base DT, enabling all ODM nodes in overlay DT to add new nodes.
+  Alternatively, you could put all SoC-related nodes in the base DT into an
+  <strong><code>soc</code></strong> node under root node as described below:
+</p>
 
 <table>
 <tr>
@@ -209,64 +251,103 @@ you could put all SoC-related nodes in the base DT into a
 </tr>
 </table>
 
+<h2 id="compressed-overlays">Using compressed overlays</h2>
+
+<p>
+  Android {{ androidPVersionNumber }} adds support for using compressed overlays
+  in the DTBO image when using version 1 of the device tree table header. 
+  When using DTBO header v1, the four least significant bits of the flags field
+  in <em>dt_table_entry</em> indicate the compression format of the DT entry.
+</p>
+
+<pre class="prettyprint">struct dt_table_entry_v1 {
+  uint32_t dt_size;
+  uint32_t dt_offset;  /* offset from head of dt_table_header */
+  uint32_t id;         /* optional, must be zero if unused */
+  uint32_t rev;        /* optional, must be zero if unused */
+  uint32_t flags;      /* For version 1 of dt_table_header, the 4 least significant bits
+                        of 'flags' will be used to indicate the compression
+                        format of the DT entry as per the enum 'dt_compression_info' */
+  uint32_t custom[3];  /* optional, must be zero if unused */
+};
+</pre>
+
+<p>
+  Currently, <code>zlib</code> and <code>gzip</code> compressions are supported.
+</p>
+
+<pre class="prettyprint">enum dt_compression_info {
+    NO_COMPRESSION,
+    ZLIB_COMPRESSION,
+    GZIP_COMPRESSION
+};
+</pre>
+
+<p>
+  Android {{ androidPVersionNumber }} adds support for testing compressed
+  overlays to the <code>VtsFirmwareDtboVerification</code> test to help you
+  verify the correctness of overlay application.
+</p>
+
 <h2 id=sample>Sample DTO implementation</h2>
-<p>The following instructions walk you through a sample implementation of DTO
-with <code>libufdt</code> (sample code below).</p>
+
+<p>
+  The following instructions walk you through a sample implementation of DTO
+  with <code>libufdt</code> (sample code below).
+</p>
 
 <h3 id=sample-instructions>Sample DTO instructions</h3>
 
 <ol>
-<li>Include libraries. To use <code>libufdt</code>, include <code>libfdt</code>
-for data structures and APIs:
+  <li>Include libraries. To use <code>libufdt</code>, include
+  <code>libfdt</code> for data structures and APIs:
 <pre class="prettyprint">
 #include &lt;libfdt.h&gt;
 #include &lt;ufdt_overlay.h&gt;
 </pre>
-</li>
-
-<li>Load main DT and overlay DT. Load <code>.dtb</code> and <code>.dtbo</code>
-from storage into memory (exact steps depend on your design). At this point, you
-should have the buffer and size of <code>.dtb</code>/<code>.dtbo</code>:
+  </li>
+  <li>Load main DT and overlay DT. Load <code>.dtb</code> and <code>.dtbo</code>
+  from storage into memory (exact steps depend on your design). At this point,
+  you should have the buffer and size of <code>.dtb</code>/<code>.dtbo</code>:
 <pre class="prettyprint">
 main_size = my_load_main_dtb(main_buf, main_buf_size)
 </pre>
 <pre class="prettyprint">
 overlay_size = my_load_overlay_dtb(overlay_buf, overlay_buf_size);
 </pre>
-</li>
-
-<li>Overlay the DTs:
-<ol>
-
-<li>Use <code>ufdt_install_blob()</code> to get the FDT header for main DT:
+  </li>
+  <li>Overlay the DTs:
+  <ol>
+    <li>Use <code>ufdt_install_blob()</code> to get the FDT header for main DT:
 <pre class="prettyprint">
 main_fdt_header = ufdt_install_blob(main_buf, main_size);
 main_fdt_size = main_size;
 </pre>
-</li>
-<li>Call <code>ufdt_apply_overlay()</code> to DTO to get a merged DT in FDT
-format:
+    </li>
+    <li>Call <code>ufdt_apply_overlay()</code> to DTO to get a merged DT in FDT
+    format:
 <pre class="prettyprint">
 merged_fdt = ufdt_apply_overlay(main_fdt_header, main_fdt_size,
                                 overlay_buf, overlay_size);
 </pre>
-</li>
-
-<li>To get the size of <code>merged_fdt</code>, use <code>dtc_totalsize()</code>:
+    </li>
+    <li>Use <code>merged_fdt</code> to get the size of
+    <code>dtc_totalsize()</code>:
 <pre class="prettyprint">
 merged_fdt_size = dtc_totalsize(merged_fdt);
 </pre>
-</li>
-
-<li>Pass merged DT to start kernel. When you start the kernel, pass merged DT to
-kernel:
+    </li>
+    <li>Pass the merged DT to start the kernel:
 <pre class="prettyprint">
 my_kernel_entry(0, machine_type, merged_fdt);
 </pre>
-</li>
-</ol></li></ol>
+    </li>
+  </ol>
+  </li>
+</ol>
 
 <h3 id=sample-code>Sample DTO code</h3>
+
 <pre class="prettyprint">
 #include &lt;libfdt.h&gt;
 #include &lt;ufdt_overlay.h&gt;