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<body class="book">
<div id="header">
<h1>_DSD (Device Specific Data) Implementation Guide</h1>
<div class="details">
<span id="author" class="author">UEFI ACPI Specification Working Group</span><br>
<span id="revnumber">version 2.0,</span>
<span id="revdate">23 April 2021</span>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div id="toc" class="toc">
<div id="toctitle" class="title">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#_introduction">1. Introduction</a>
<ul class="sectlevel2">
<li><a href="#_copyright_and_license_information">1.1. Copyright and License Information</a></li>
<li><a href="#_change_log">1.2. Change Log</a></li>
<li><a href="#_quick_start_guide">1.3. Quick Start Guide</a></li>
<li><a href="#_terms">1.4. Terms</a></li>
<li><a href="#_conventions">1.5. Conventions</a></li>
<li><a href="#_references">1.6. References</a></li>
</ul>
</li>
<li><a href="#_general_recommendations">2. General Recommendations</a>
<ul class="sectlevel2">
<li><a href="#_using_dsd_versus_dsm">2.1. Using <code>_DSD</code> versus <code>_DSM</code></a></li>
<li><a href="#_general_dsd_definition_template">2.2. General <code>_DSD</code> Definition Template</a></li>
</ul>
</li>
<li><a href="#_well_known_dsd_uuids_and_data_structure_formats">3. Well-Known <code>_DSD</code> UUIDs and Data Structure Formats</a>
<ul class="sectlevel2">
<li><a href="#_device_properties_uuid">3.1. Device Properties UUID</a>
<ul class="sectlevel3">
<li><a href="#_data_format_definition">3.1.1. Data Format Definition</a></li>
<li><a href="#_device_properties_uuid_rules">3.1.2. Device Properties UUID Rules</a></li>
<li><a href="#_device_property_naming">3.1.3. Device Property Naming</a></li>
<li><a href="#_adding_uefi_device_properties">3.1.4. Adding UEFI Device Properties</a></li>
<li><a href="#_registering_prefixes">3.1.5. Registering Prefixes</a></li>
<li><a href="#_examples">3.1.6. Examples</a></li>
<li><a href="#_dependencies_on_crs_when_using_dsd">3.1.7. Dependencies on <code>_CRS</code> When Using <code>_DSD</code></a></li>
</ul>
</li>
<li><a href="#_hierarchical_data_extension_uuid">3.2. Hierarchical Data Extension UUID</a>
<ul class="sectlevel3">
<li><a href="#_data_format_definition_2">3.2.1. Data Format Definition</a></li>
<li><a href="#_example">3.2.2. Example</a></li>
</ul>
</li>
<li><a href="#_device_graph_uuid">3.3. Device Graph UUID</a>
<ul class="sectlevel3">
<li><a href="#_data_format_definition_3">3.3.1. Data Format Definition</a></li>
<li><a href="#_example_2">3.3.2. Example</a></li>
<li><a href="#_known_device_graph_uuids">3.3.3. Known Device Graph UUIDs</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#_deprecated_device_properties">Appendix A: Deprecated Device Properties</a></li>
<li><a href="#_uefi_defined_device_property_usage">Appendix B: UEFI Defined Device Property Usage</a></li>
<li><a href="#_known_device_property_prefixes">Appendix C: Known Device Property Prefixes</a></li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_introduction">1. Introduction</h2>
<div class="sectionbody">
<div class="paragraph">
<p>This is the ACPI _DSD Implementation Guide. This guide and its associated
documents provide recommendations on the use of the _DSD (Device Specific
Data) object as defined in the ACPI Specification <a href="#ACPI">[ACPI]</a>. The _DSD
object is a device specific configuration object, intended for firmware
and software engineers implementing _DSD or designing software that will
use information supplied by the object.</p>
</div>
<div class="paragraph">
<p>The _DSD, as defined by the ACPI Specification, returns a Package, the
first and every odd element of which is a Universal Unique Identifier
(UUID) and every even element of which is a Package (Data Structure),
where each of the UUIDs dictates the format of the Data Structure
immediately following it. The well-known UUIDs to use in the _DSD
output and the Data Structure formats associated with them are also
specified in this document.</p>
</div>
<div class="sect2">
<h3 id="_copyright_and_license_information">1.1. Copyright and License Information</h3>
<div class="paragraph">
<p>The _DSD Implementation Guide is © 2021, Unified Extensible Firmware
Interface (UEFI) Forum, Inc. More specifically, content is under the
purview of the ACPI Specification Working Group (ASWG) <<a href="mailto:aswg@uefi.org">aswg@uefi.org</a>>.</p>
</div>
<div class="paragraph">
<p>The _DSD Implementation Guide is licensed under the Creative Commons
Attribution 4.0 International License (CC-BY 4.0). The full license
text is available at <a href="https://creativecommons.org/licenses/by/4.0/" class="bare">https://creativecommons.org/licenses/by/4.0/</a>.</p>
</div>
</div>
<div class="sect2">
<h3 id="_change_log">1.2. Change Log</h3>
<div class="ulist">
<ul>
<li>
<p>Version 2.0</p>
<div class="ulist">
<ul>
<li>
<p>Initial conversion to asciidoc from original v1.2.</p>
</li>
<li>
<p>General text rewrites and reformatting.</p>
</li>
<li>
<p>Expand the Terms section.</p>
</li>
<li>
<p>Add a licensing section.</p>
</li>
<li>
<p>Add a bibliography and references section.</p>
</li>
<li>
<p>Add in process and naming recommendations.</p>
</li>
</ul>
</div>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="_quick_start_guide">1.3. Quick Start Guide</h3>
<div class="ulist">
<ul>
<li>
<p><strong><em>If you are new to ACPI</em></strong>: please start with the ACPI specification
(see <a href="#ACPI">[ACPI]</a>) and in particular section 6.2.5, "_DSD (Device Specific
Data)".</p>
</li>
<li>
<p><strong><em>If you are new to using <code>_DSD</code> in ACPI</em></strong>: please start by reading
or reviewing section 6.2.5, "_DSD (Device Specific Data)" in <a href="#ACPI">[ACPI]</a>.</p>
</li>
<li>
<p><strong><em>If you are looking for details about a specific <code>_DSD</code> UUID</em></strong>: these
are all defined in section
<a href="#_well_known_dsd_uuids_and_data_structure_formats">Well-Known <code>_DSD</code> UUIDs and Data Structure Formats</a>. The UUIDs are:</p>
<div class="ulist">
<ul>
<li>
<p>Device Properties UUID: in section <a href="#_device_properties_uuid">Device Properties UUID</a></p>
</li>
<li>
<p>Hierarchical Data Extension UUID: in section
<a href="#_hierarchical_data_extension_uuid">Hierarchical Data Extension UUID</a></p>
</li>
<li>
<p>Device Graph UUID: in section <a href="#_device_graph_uuid">Device Graph UUID</a></p>
</li>
</ul>
</div>
</li>
<li>
<p><strong><em>If you are looking for currently defined UEFI Device Properties</em></strong>:
see section
<a href="#_uefi_defined_device_property_usage">UEFI Defined Device Property Usage</a>.</p>
</li>
<li>
<p><strong><em>If you are looking for currently defined Device Property Prefixes</em></strong>:
see section
<a href="#_known_device_property_prefixes">Known Device Property Prefixes</a>.</p>
</li>
<li>
<p><strong><em>If you wish to register a Device Property Prefix</em></strong>: please see section
<a href="#_known_device_property_prefixes">Known Device Property Prefixes</a>
for currently defined prefixes, and section <a href="#_registering_prefixes">Registering Prefixes</a>.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="_terms">1.4. Terms</h3>
<div class="paragraph">
<p>The key words <strong>MUST</strong>, <strong>MUST NOT</strong>, <strong>REQUIRED</strong>, <strong>SHALL</strong>, <strong>SHALL
NOT</strong>, <strong>SHOULD</strong>, <strong>SHOULD NOT</strong>, <strong>RECOMMENDED</strong>, <strong>MAY</strong>, and
<strong>OPTIONAL</strong> in this document are to be interpreted as described in
IETF <a href="#RFC2119">[RFC2119]</a>.</p>
</div>
<div class="paragraph">
<p>The following additional terms are used in this document:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">ACPI</dt>
<dd>
<p>Advanced Configuration and Power Interface specification.</p>
</dd>
<dt class="hdlist1">ASWG</dt>
<dd>
<p>ACPI Specification Working Group</p>
</dd>
<dt class="hdlist1">DCO</dt>
<dd>
<p>Developer’s Certificate of Origin <a href="#DCO">[DCO]</a></p>
</dd>
<dt class="hdlist1">Device</dt>
<dd>
<p>Hardware component or set of interrelated hardware registers.</p>
</dd>
<dt class="hdlist1">Device ID</dt>
<dd>
<p>Plug and Play ID or ACPI ID of a device.</p>
</dd>
<dt class="hdlist1">GUID</dt>
<dd>
<p>Globally Unique Identifier. A 128-bit value used to uniquely
name entities. A unique GUID can be generated by an individual
without the help of a centralized authority. This allows the
generation of names that will never conflict, even among multiple,
unrelated parties.</p>
</dd>
<dt class="hdlist1">OSPM</dt>
<dd>
<p>Operating System Power Management</p>
</dd>
<dt class="hdlist1">PNP</dt>
<dd>
<p>Plug and Play</p>
</dd>
<dt class="hdlist1">UEFI</dt>
<dd>
<p>Unified Extensible Firmware Interface</p>
</dd>
<dt class="hdlist1">UUID</dt>
<dd>
<p>Universal Unique Identifier, a synonym for GUID.</p>
</dd>
</dl>
</div>
</div>
<div class="sect2">
<h3 id="_conventions">1.5. Conventions</h3>
<div class="paragraph">
<p>The following typographic conventions are used:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">Computer Text</dt>
<dd>
<p><code>monospace text</code> is used to represent computer
inputs or outputs.</p>
</dd>
<dt class="hdlist1">Stress</dt>
<dd>
<p><strong>bold text</strong> is used to add emphasis to terms.</p>
</dd>
<dt class="hdlist1">Terms</dt>
<dd>
<p><em>italic text</em> is used to highlight important terminology.</p>
</dd>
</dl>
</div>
</div>
<div class="sect2">
<h3 id="_references">1.6. References</h3>
<div class="ulist bibliography">
<ul class="bibliography">
<li>
<p><a id="ACPI"></a>[ACPI] Advanced Configuration and Power Interface (ACPI) Specification,
Version 6.3, January 2019. Copyright (c) 2018, Unified Extensible
Firmware Interface (UEFI) Forum, Inc. <a href="https://uefi.org/specifications" class="bare">https://uefi.org/specifications</a></p>
</li>
<li>
<p><a id="DCO"></a> Developer’s Certificate of Origin. <a href="https://developercertificate.org/" class="bare">https://developercertificate.org/</a></p>
</li>
<li>
<p><a id="RFC2119"></a>[RFC2119] <a href="https://www.ietf.org/rfc/rfc2119.txt" class="bare">https://www.ietf.org/rfc/rfc2119.txt</a></p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_general_recommendations">2. General Recommendations</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_using_dsd_versus_dsm">2.1. Using <code>_DSD</code> versus <code>_DSM</code></h3>
<div class="paragraph">
<p>Although in principle the <code>_DSM</code> (Device Specific Method) may be used to
implement the functionality provided by <code>_DSD</code>, it is not recommended to
do so. Since <code>_DSD</code> is better suited for providing device configuration
data, it should be used for this purpose where applicable. However, there
are situations in which where using <code>_DSM</code> instead of <code>_DSD</code> needs to
be considered. Generally, all situations in which it would be necessary to
implement <code>_DSD</code> as a <code>Method()</code> for technical reasons fall into this
category, but in particular <code>_DSD</code> should not write into device
registers in addition to returning the data. In addition to that, <code>_DSD</code>
must return the same data every time it is evaluated, so if that cannot
be guaranteed, <code>_DSM</code> has to be used instead.</p>
</div>
</div>
<div class="sect2">
<h3 id="_general_dsd_definition_template">2.2. General <code>_DSD</code> Definition Template</h3>
<div class="paragraph">
<p>Wherever possible, it is recommended to implement <code>_DSD</code> as a <code>Name()</code>
as opposed to a <code>Method()</code> in order to avoid possible programmatic
errors and computational overhead that are sometimes associated with
the execution of AML (ASL Machine Language) code. In that case the
definition of <code>_DSD</code> should follow this template:</p>
</div>
<div class="literalblock">
<div class="title">General <code>_DSD</code> Template</div>
<div class="content">
<pre> Name (_DSD, Package () {
ToUUID("UUID1"),
Package () {
...
},
ToUUID("UUID2"),
Package () {
...
},
...
ToUUID("UUIDn"),
Package () {
...
}
})</pre>
</div>
</div>
<div class="paragraph">
<p>As noted in the introduction, <code>_DSD</code> returns a <code>Package()</code> with
one or more pairs of elements. The first element of each pair — i.e.,
the first and every following odd element of the total <code>Package()</code> — is a Universal Unique Identifier (UUID). The second element of each
pair — and every even element of the total <code>Package()</code> — is another
<code>Package()</code> Data Structure. Each UUID dictates the format and content
of the Data Structure immediately following it.</p>
</div>
<div class="paragraph">
<p>Only the well-known UUIDs and their corresponding Data Structures defined
in this guide should be used. The behavior of any other UUIDs and Data
Structures are <strong>undefined</strong>.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_well_known_dsd_uuids_and_data_structure_formats">3. Well-Known <code>_DSD</code> UUIDs and Data Structure Formats</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_device_properties_uuid">3.1. Device Properties UUID</h3>
<div class="paragraph">
<p>This section specifies the data format associated with UUID:</p>
</div>
<div class="paragraph">
<p><strong>daffd814-6eba-4d8c-8a91-bc9bbf4aa301</strong></p>
</div>
<div class="paragraph">
<p>(Device Properties UUID) for the <code>_DSD</code> (Device Specific Data) ACPI
device configuration object.</p>
</div>
<div class="sect3">
<h4 id="_data_format_definition">3.1.1. Data Format Definition</h4>
<div class="paragraph">
<p>The device properties UUID:</p>
</div>
<div class="paragraph">
<p><strong>daffd814-6eba-4d8c-8a91-bc9bbf4aa301</strong></p>
</div>
<div class="paragraph">
<p>defines the data format for the <code>Package()</code> (Data Structure) immediately
following it as a list of Packages of length two (2), known as Properties.
The first element of each Property (the Key) must be a String and the
second element (the Value) must be:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>an Integer,</p>
</li>
<li>
<p>a String,</p>
</li>
<li>
<p>a Reference, or</p>
</li>
<li>
<p>a Package consisting entirely of Integer, String, or Reference objects
(and specifically not containing a nested Package).</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The list of valid Keys, and the format and interpretation of the
corresponding Values, depends on the PNP or ACPI device ID (e.g., <code>_HID</code>)
of the Device containing the <code>_DSD</code>. For instance, the PNP device ID
returned by <code>_HID</code> for Device object <code>MDEV</code> below will determine the
list of valid Keys and the corresponding Value data formats for that
Device object’s <code>_DSD</code>.</p>
</div>
<div class="literalblock">
<div class="content">
<pre>Device (MDEV) {
Name (_HID, "PNP####")
Name (_DSD, Package () {
ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
Package () {
Package (2) {...}, // Property 1
Package (2) {...}, // Property 2
...
Package (2) {...} // Property n
}
})
...
}</pre>
</div>
</div>
<div class="paragraph">
<p>In the context of the Device Properties UUID, each Property is a
characteristic of the hardware itself or the way it is used in the
system in which it is incorporated, as opposed to software configuration
data. As such, the list of valid property Keys and Value data formats
associated with them must be defined by the device vendor in a way that
is independent of the firmware interface to be used on any given platform.</p>
</div>
<div class="paragraph">
<p>Multiple Properties with the same Key in a single Data Structure associated
with the Device Properties UUID are not permitted.</p>
</div>
</div>
<div class="sect3">
<h4 id="_device_properties_uuid_rules">3.1.2. Device Properties UUID Rules</h4>
<div class="paragraph">
<p>Properties described in a Device Properties UUID <code>_DSD</code> are intended
to be used in addition to, and not instead of, the existing mechanisms
defined by the ACPI specification. For this reason, as a rule, Device
Properties should only be used if the ACPI specification does not make
direct provisions for handling the underlying use case. ACPI provides
a number of generic interfaces to operating systems kernels, and
these should continue to function without requiring the kernels to
directly parse a device properties <code>_DSD</code>. For example, properties
that describe how to turn voltage regulators, or clocks, on and off,
should not be used, as these should be managed via power resource
<code>_ON</code>/<code>_OFF</code> methods, or device <code>_PSx</code> methods.</p>
</div>
<div class="paragraph">
<p>It is not permitted to use Properties in a data structure associated
with the Device Properties UUID to provide the OSPM and device drivers
with the same information that can be provided as device resources
via <code>_CRS</code> (Current Resource Settings). In case of any conflicts
between such Properties and the information returned by <code>_CRS</code>, the
latter always takes precedence.</p>
</div>
<div class="paragraph">
<p>Properties of a Device may depend on the order of the resources
provided via <code>_CRS</code> or the order of the resources of a particular
type. For instance, a Property may identify an IRQ via an index into
the IRQ resources provided via <code>_CRS</code> rather than providing an absolute
IRQ number. This avoids duplication between the Properties and <code>_CRS</code>,
making it easier to change the resources of a Device in one place.</p>
</div>
</div>
<div class="sect3">
<h4 id="_device_property_naming">3.1.3. Device Property Naming</h4>
<div class="paragraph">
<p>While the Key for a Property may be any String, there is a very high
probability of name collision. For example, two vendors could use the
String <code>"serial-number"</code> as a Key. The problem is that each vendor may
have very different use cases for the Value. One use case could be a
Boolean value (<code>"yes"</code> means the device has a read-only register that
contains a serial number, <code>"no"</code> means the device has no such register).
A second use case could be that the value is the actual serial number
("abcde-123456").</p>
</div>
<div class="paragraph">
<p>It is highly recommended that each vendor prefix their Key name with
their registered PNP or ACPI vendor ID in order to avoid name collisions.
What the vendor decides to use after the prefix is completely up to their
own discretion. For example, Vendor ABCD would use <code>abcd-serial-number</code>
instead of <code>serial-number</code>, especially if the word or term is known to
be in common use. Please see <a href="#_registering_prefixes">Registering Prefixes</a> for instructions
on obtaining a vendor prefix.</p>
</div>
<div class="paragraph">
<p>Due to historical usage, Appendix A <a href="#_deprecated_device_properties">Deprecated Device Properties</a>
contains a list of Keys that do not have any prefix at all. These should
not be used in the future; they should be considered deprecated. In
Appendix B
<a href="#_uefi_defined_device_property_usage:">UEFI Defined Device Property Usage</a>,
prefixed names for these same Keys are defined and should be used henceforth.</p>
</div>
<div class="paragraph">
<p>The reason these older Key definitions have no prefix is that there
was at one time the concept of a global namespace for these Keys, and
a process for registering them and defining them. As a practical matter,
hardware and software vendors have ignored the whole thing and used the
Keys in Appendix A as <em>de facto</em> standards. While we still have the
idea of a global namespace for Keys, from now on these must be prefixed
with <code>uefi-</code> in the interest of avoiding name collisions.</p>
</div>
<div class="paragraph">
<p>Property names that are not one of those grandfathered in through
Appendix A, or defined in Appendix B, or use a prefix not listed in
Appendix C must not be used. The use of <code>_DSD</code> Device Properties
under those circumstance may have unpredictable outcomes.</p>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">
<div class="title">Important</div>
</td>
<td class="content">
<div class="title">There is no need to change existing implementations.</div>
<div class="paragraph">
<p>As a pragmatic matter, the use of prefixes and control of the name
space as described here is <strong>optional</strong> so that we do not disturb
existing OS implementations and usage. Existing Device Properties can
continue to be used as they are today; there is no requirement to change
them to use the new prefix scheme.</p>
</div>
<div class="paragraph">
<p>However, we <strong>highly recommend</strong> that prefixes be used and that they be
registered from this point on for future or new Device Properties. It
is ultimately in everyone’s best interest to be clear on who owns what
Device Properties, and who is responsible for defining them.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
<div class="sect3">
<h4 id="_adding_uefi_device_properties">3.1.4. Adding UEFI Device Properties</h4>
<div class="paragraph">
<p>In order to create a Device Property in the <code>uefi</code> namespace, it must
be provided as a merge request (MR) to this document via github (see
<a href="https://github.com/UEFI/DSD-Guide" class="bare">https://github.com/UEFI/DSD-Guide</a>, and the file <code>src/dsd-guide.adoc</code>).
When submitting the MR, please provide a rationale for singling out
this Key/Value pair as something that needs to be defined globally.
Further, please provide a description of how the Key/Value pair is to
be used, with a definition of the allowed values, and a brief example.
Something similar to the definitions in Appendix B
<a href="#_uefi_defined_device_property_usage:">UEFI Defined Device Property Usage</a>
will speed up the process.</p>
</div>
<div class="paragraph">
<p>Each MR will be reviewed by the UEFI Forum (specifically, the ACPI
Specification Working Group or ASWG) at the next available opportunity.
Acceptance, refusal, or suggested improvements, will be discussed on
github.</p>
</div>