service: device-tree node vpd to d-bus hw id data

A daemon for transferring Viable Product Data (VPD) from device-tree
nodes to D-Bus as described in the design doc @
https://gerrit.openbmc.org/c/openbmc/docs/+/66369

and discussed in this Technical Oversight Forum topic @
openbmc/technical-oversight-forum#38

Tested:
Ensure 'model' and/or 'serial-number' nodes are populated in
/proc/device-tree. Can be hardcoded into platform DTS via
linux-kernel recipe if needed.

'''
After OBMC boot, calling
> busctl introspect xyz.openbmc_project.MachineContext /xyz/openbmc_project/MachineContext

produces the following output:

NAME                                          TYPE      SIGNATURE  RESULT/VALUE  FLAGS
...
xyz.openbmc_project.Inventory.Decorator.Asset interface -          -             -
.BuildDate                                    property  s          ""            emits-change writable
.Manufacturer                                 property  s          ""            emits-change writable
.Model                                        property  s          "hpe,dl360"   emits-change writable
.PartNumber                                   property  s          ""            emits-change writable
.SerialNumber                                 property  s          "t5texpl"     emits-change writable
...

Note: Writing to one of these properties will update the property on D-Bus without affecting the
underlying device-tree node. An 'updated' event will be fired, so Entity-Manager probes monitoring
a given property would recognize the new value and key off it.
'''

Change-Id: Id52d1fc3b26010c864c7e64d3dfdf0a2b5de9294
Signed-off-by: Chris Sides <[email protected]>

Author: csides-hpe

.gitignore

@@ -1,6 +1,5 @@
 build*/*
 subprojects/*
 !subprojects/*.wrap
-subprojects/phosphor-dbus-interfaces.wrap
 !subprojects/.clang-tidy
 !subprojects/.clang-format

meson.build

@@ -34,6 +34,10 @@ if get_option('fru-device')
     i2c = cpp.find_library('i2c')
 endif
 
+if get_option('devicetree-vpd')
+    phosphor_dbus_interfaces_dep = dependency('phosphor-dbus-interfaces', include_type: 'system')
+endif
+
 nlohmann_json_dep = dependency('nlohmann_json', include_type: 'system')
 sdbusplus = dependency('sdbusplus', include_type: 'system')
 phosphor_logging_dep = dependency('phosphor-logging')

meson_options.txt

@@ -2,11 +2,14 @@ option(
     'tests', type: 'feature', description: 'Build tests.',
 )
 option(
-    'fru-device', type: 'boolean', description: 'Build fru-device.',
+    'fru-device', type: 'boolean', description: 'Build fru-device VPD parser.',
 )
 option(
     'fru-device-resizefru', value : false, type: 'boolean', description: 'Allow FruDevice to resize FRU areas.',
 )
+option(
+    'devicetree-vpd', type: 'boolean', description: 'Build device-tree VPD parser'
+)
 option(
     'validate-json', type: 'boolean', value: true, description: 'Run JSON schema validation during the build.',
 )

service_files/devicetree-vpd-parser.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=Makes data from device-tree nodes avaliable thru D-Bus
+After=dbus.service
+
+[Service]
+ExecStart=/usr/libexec/entity-manager/devicetree-vpd-parser
+Type=dbus
+BusName=xyz.openbmc_project.MachineContext
+
+[Install]
+WantedBy=basic.target

service_files/meson.build

@@ -1,6 +1,7 @@
 unit_files = [
     ['xyz.openbmc_project.FruDevice.service', 'fru-device'],
     ['xyz.openbmc_project.EntityManager.service', ''],
+    ['devicetree-vpd-parser.service', 'devicetree-vpd'],
 ]
 
 foreach u : unit_files

src/devicetree_vpd_parser.cpp

@@ -0,0 +1,44 @@
+#include "machine_context.hpp"
+
+#include <memory>
+
+int main()
+{
+    static constexpr auto reqDBusPath = "/xyz/openbmc_project/MachineContext";
+    static constexpr auto reqDBusName = "xyz.openbmc_project.MachineContext";
+
+    /*Note: OpenBMC convention typically has service name = bus name,
+    where the bus name is representative of the underlying hardware.
+
+    In the case of MachineContext, the BMC is not gathering data from
+    specific hardware, but is instead parsing device-tree nodes for
+    context about the hardware OpenBMC is running on.
+
+    Because the VPD data being parsed is coming from device-tree,
+    the daemon and matching service name reflect that.
+
+    Because the parsed data represents 'machine context' data,
+    the bus name and associated path the daemon writes to
+    reflects that instead.
+    */
+
+    sdbusplus::async::context ctx;
+    sdbusplus::server::manager_t manager{ctx, reqDBusPath};
+
+    std::unique_ptr<MachineContext> mc = nullptr;
+    if (MachineContext::keyNodeExists())
+    {
+        mc = std::make_unique<MachineContext>(ctx, reqDBusPath);
+        mc->populateFromDeviceTree();
+    }
+
+    // NOLINTNEXTLINE(readability-static-accessed-through-instance)
+    ctx.spawn([](sdbusplus::async::context& ctx) -> sdbusplus::async::task<> {
+        ctx.request_name(reqDBusName);
+        co_return;
+    }(ctx));
+
+    ctx.run();
+
+    return 0;
+};

src/machine_context.cpp

@@ -0,0 +1,45 @@
+/*
+// Copyright (c) 2024 Hewlett Packard Enterprise
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+*/
+
+#include "machine_context.hpp"
+
+#include <filesystem>
+#include <fstream>
+
+void MachineContext::populateFromDeviceTree()
+{
+    std::string nodeVal;
+    std::ifstream vpdStream(nodeBasePath + std::string("model"));
+    if (vpdStream && std::getline(vpdStream, nodeVal))
+    {
+        MachineContext::Asset::model(nodeVal);
+        vpdStream.close();
+    }
+
+    vpdStream.open(nodeBasePath + std::string("serial-number"));
+    if (vpdStream && std::getline(vpdStream, nodeVal))
+    {
+        MachineContext::Asset::serial_number(nodeVal);
+        vpdStream.close();
+    }
+};
+
+bool MachineContext::keyNodeExists()
+{
+    std::filesystem::path nodePath{nodeBasePath + std::string("model")};
+
+    return std::filesystem::exists(nodePath);
+};

src/machine_context.hpp

@@ -0,0 +1,37 @@
+/*
+// Copyright (c) 2024 Hewlett Packard Enterprise
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+*/
+
+#pragma once
+
+#include <sdbusplus/async.hpp>
+#include <xyz/openbmc_project/Inventory/Decorator/Asset/aserver.hpp>
+
+class MachineContext :
+    public sdbusplus::aserver::xyz::openbmc_project::inventory::decorator::
+        Asset<MachineContext>
+{
+  public:
+    explicit MachineContext(sdbusplus::async::context& ctx, auto path) :
+        sdbusplus::aserver::xyz::openbmc_project::inventory::decorator::Asset<
+            MachineContext>(ctx, path) {};
+
+    void populateFromDeviceTree();
+
+    static bool keyNodeExists();
+
+  private:
+    static constexpr auto nodeBasePath = "/proc/device-tree/";
+};

src/meson.build

@@ -49,3 +49,19 @@ if get_option('fru-device')
         install_dir: installdir,
     )
 endif
+
+if get_option('devicetree-vpd')
+    cpp_args_fd = cpp_args
+    executable(
+        'devicetree-vpd-parser',
+        'machine_context.cpp',
+        'devicetree_vpd_parser.cpp',
+        cpp_args: cpp_args_fd,
+        dependencies: [
+            sdbusplus,
+            phosphor_dbus_interfaces_dep,
+        ],
+        install: true,
+        install_dir: installdir,
+    )
+endif

subprojects/phosphor-dbus-interfaces.wrap

@@ -0,0 +1,7 @@
+
+[wrap-git]
+url = https://github.com/openbmc/phosphor-dbus-interfaces.git
+revision = HEAD
+
+[provide]
+phosphor-dbus-interfaces = phosphor_dbus_interfaces_dep