nvidia-gpu: introduce notion of a device

Perform device discovery tasks only once per device to prepare for
introducing additional gpu sensors.

In the current implementation, sensor updates and device discovery via
MCTP are managed within a single class for simplicity. However, since a
GPU device typically includes multiple sensors, performing device
discovery for each individual sensor is inefficient. Instead, it would
be more effective to execute device discovery once per device.

Tested: Build an image for gb200nvl-obmc machine with the following
patches cherry picked. This patches are needed to enable the mctp stack.
https://gerrit.openbmc.org/c/openbmc/openbmc/+/79422

```
$ curl -k -u 'root:0penBmc' https://10.137.203.137/redfish/v1/Chassis/NVIDIA_GB200_1/Sensors/temperature_NVIDIA_GB200_GPU_0_TEMP_0
{
  "@odata.id": "/redfish/v1/Chassis/NVIDIA_GB200_1/Sensors/temperature_NVIDIA_GB200_GPU_0_TEMP_0",
  "@odata.type": "#Sensor.v1_2_0.Sensor",
  "Id": "temperature_NVIDIA_GB200_GPU_0_TEMP_0",
  "Name": "NVIDIA GB200 GPU 0 TEMP 0",
  "Reading": 37.6875,
  "ReadingRangeMax": 127.0,
  "ReadingRangeMin": -128.0,
  "ReadingType": "Temperature",
  "ReadingUnits": "Cel",
  "Status": {
    "Health": "OK",
    "State": "Enabled"
  }
}%
```

Change-Id: Ie3dcd43caa031b4aaa61d8be3f5d71aefd53bc9a
Signed-off-by: Harshit Aghera <haghera@nvidia.com>
diff --git a/src/nvidia-gpu/NvidiaDeviceDiscovery.cpp b/src/nvidia-gpu/NvidiaDeviceDiscovery.cpp
new file mode 100644
index 0000000..adb21ea
--- /dev/null
+++ b/src/nvidia-gpu/NvidiaDeviceDiscovery.cpp
@@ -0,0 +1,357 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION &
+ * AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "NvidiaDeviceDiscovery.hpp"
+
+#include "NvidiaGpuDevice.hpp"
+#include "Utils.hpp"
+
+#include <bits/basic_string.h>
+
+#include <MctpRequester.hpp>
+#include <NvidiaGpuMctpVdm.hpp>
+#include <OcpMctpVdm.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/container/flat_map.hpp>
+#include <phosphor-logging/lg2.hpp>
+#include <sdbusplus/asio/connection.hpp>
+#include <sdbusplus/asio/object_server.hpp>
+#include <sdbusplus/message.hpp>
+#include <sdbusplus/message/native_types.hpp>
+
+#include <algorithm>
+#include <array>
+#include <cstdint>
+#include <memory>
+#include <span>
+#include <string>
+#include <utility>
+#include <variant>
+#include <vector>
+
+void processQueryDeviceIdResponse(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& conn,
+    mctp::MctpRequester& mctpRequester, const SensorConfigs& configs,
+    const std::string& path, uint8_t eid, int sendRecvMsgResult,
+    std::span<uint8_t> queryDeviceIdentificationResponse)
+{
+    if (sendRecvMsgResult != 0)
+    {
+        lg2::error(
+            "Error processing MCTP endpoint with eid {EID} : sending message over MCTP failed, rc={RC}",
+            "EID", eid, "RC", sendRecvMsgResult);
+        return;
+    }
+
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode = 0;
+    uint8_t responseDeviceType = 0;
+    uint8_t responseInstanceId = 0;
+
+    auto rc = gpu::decodeQueryDeviceIdentificationResponse(
+        queryDeviceIdentificationResponse, cc, reasonCode, responseDeviceType,
+        responseInstanceId);
+
+    if (rc != 0 || cc != ocp::accelerator_management::CompletionCode::SUCCESS)
+    {
+        lg2::error(
+            "Error processing MCTP endpoint with eid {EID} : decode failed, rc={RC}, cc={CC}, reasonCode={RESC}",
+            "EID", eid, "RC", rc, "CC", cc, "RESC", reasonCode);
+        return;
+    }
+
+    if (responseDeviceType ==
+        static_cast<uint8_t>(gpu::DeviceIdentification::DEVICE_GPU))
+    {
+        lg2::info(
+            "Found the GPU with EID {EID}, DeviceType {DEVTYPE}, InstanceId {IID}.",
+            "EID", eid, "DEVTYPE", responseDeviceType, "IID",
+            responseInstanceId);
+
+        auto gpuName = configs.name + '_' + std::to_string(responseInstanceId);
+
+        gpuDevices[gpuName] = std::make_shared<GpuDevice>(
+            configs, gpuName, path, conn, eid, io, mctpRequester, objectServer);
+    }
+}
+
+void queryDeviceIdentification(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& conn,
+    mctp::MctpRequester& mctpRequester, const SensorConfigs& configs,
+    const std::string& path, uint8_t eid)
+{
+    auto queryDeviceIdentificationRequest = std::make_shared<
+        std::array<uint8_t, sizeof(gpu::QueryDeviceIdentificationRequest)>>();
+
+    auto queryDeviceIdentificationResponse = std::make_shared<
+        std::array<uint8_t, sizeof(gpu::QueryDeviceIdentificationResponse)>>();
+
+    auto rc = gpu::encodeQueryDeviceIdentificationRequest(
+        0, *queryDeviceIdentificationRequest);
+    if (rc != 0)
+    {
+        lg2::error(
+            "Error processing MCTP endpoint with eid {EID} : encode failed, rc={RC}",
+            "EID", eid, "RC", rc);
+        return;
+    }
+
+    mctpRequester.sendRecvMsg(
+        eid, *queryDeviceIdentificationRequest,
+        *queryDeviceIdentificationResponse,
+        [&io, &objectServer, &gpuDevices, conn, &mctpRequester, configs, path,
+         eid, queryDeviceIdentificationRequest,
+         queryDeviceIdentificationResponse](int sendRecvMsgResult) {
+            processQueryDeviceIdResponse(
+                io, objectServer, gpuDevices, conn, mctpRequester, configs,
+                path, eid, sendRecvMsgResult,
+                *queryDeviceIdentificationResponse);
+        });
+}
+
+void processEndpoint(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& conn,
+    mctp::MctpRequester& mctpRequester, const SensorConfigs& configs,
+    const std::string& path, const boost::system::error_code& ec,
+    const SensorBaseConfigMap& endpoint)
+{
+    if (ec)
+    {
+        lg2::error("Error processing MCTP endpoint: Error:{ERROR}", "ERROR",
+                   ec.message());
+        return;
+    }
+
+    auto hasEid = endpoint.find("EID");
+    uint8_t eid{};
+
+    if (hasEid != endpoint.end())
+    {
+        const auto* eidPtr = std::get_if<uint8_t>(&hasEid->second);
+        if (eidPtr != nullptr)
+        {
+            eid = *eidPtr;
+        }
+        else
+        {
+            lg2::error(
+                "Error processing MCTP endpoint: Property EID does not have valid type.");
+            return;
+        }
+    }
+    else
+    {
+        lg2::error(
+            "Error processing MCTP endpoint: Property EID not found in the configuration.");
+        return;
+    }
+
+    auto hasMctpTypes = endpoint.find("SupportedMessageTypes");
+    std::vector<uint8_t> mctpTypes{};
+
+    if (hasMctpTypes != endpoint.end())
+    {
+        const auto* mctpTypePtr =
+            std::get_if<std::vector<uint8_t>>(&hasMctpTypes->second);
+        if (mctpTypePtr != nullptr)
+        {
+            mctpTypes = *mctpTypePtr;
+        }
+        else
+        {
+            lg2::error(
+                "Error processing MCTP endpoint with eid {EID} : Property SupportedMessageTypes does not have valid type.",
+                "EID", eid);
+            return;
+        }
+    }
+    else
+    {
+        lg2::error(
+            "Error processing MCTP endpoint with eid {EID} : Property SupportedMessageTypes not found in the configuration.",
+            "EID", eid);
+        return;
+    }
+
+    if (std::find(mctpTypes.begin(), mctpTypes.end(),
+                  ocp::accelerator_management::messageType) != mctpTypes.end())
+    {
+        lg2::info("Found OCP MCTP VDM Endpoint with ID {EID}", "EID", eid);
+        queryDeviceIdentification(io, objectServer, gpuDevices, conn,
+                                  mctpRequester, configs, path, eid);
+    }
+}
+
+void queryEndpoints(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& conn,
+    mctp::MctpRequester& mctpRequester, const SensorConfigs& configs,
+    const std::string& path, const boost::system::error_code& ec,
+    const GetSubTreeType& ret)
+{
+    if (ec)
+    {
+        lg2::error("Error processing MCTP endpoints: {ERROR}", "ERROR",
+                   ec.message());
+        return;
+    }
+
+    if (ret.empty())
+    {
+        return;
+    }
+
+    for (const auto& [objPath, services] : ret)
+    {
+        for (const auto& [service, ifaces] : services)
+        {
+            for (const auto& iface : ifaces)
+            {
+                if (iface == "xyz.openbmc_project.MCTP.Endpoint")
+                {
+                    conn->async_method_call(
+                        [&io, &objectServer, &gpuDevices, conn, &mctpRequester,
+                         configs, path](const boost::system::error_code& ec,
+                                        const SensorBaseConfigMap& endpoint) {
+                            processEndpoint(io, objectServer, gpuDevices, conn,
+                                            mctpRequester, configs, path, ec,
+                                            endpoint);
+                        },
+                        service, objPath, "org.freedesktop.DBus.Properties",
+                        "GetAll", iface);
+                }
+            }
+        }
+    }
+}
+
+void discoverDevices(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& conn,
+    mctp::MctpRequester& mctpRequester, const SensorConfigs& configs,
+    const std::string& path)
+{
+    std::string searchPath{"/au/com/codeconstruct/"};
+    std::vector<std::string> ifaceList{{"xyz.openbmc_project.MCTP.Endpoint"}};
+
+    conn->async_method_call(
+        [&io, &objectServer, &gpuDevices, conn, &mctpRequester, configs,
+         path](const boost::system::error_code& ec, const GetSubTreeType& ret) {
+            queryEndpoints(io, objectServer, gpuDevices, conn, mctpRequester,
+                           configs, path, ec, ret);
+        },
+        "xyz.openbmc_project.ObjectMapper",
+        "/xyz/openbmc_project/object_mapper",
+        "xyz.openbmc_project.ObjectMapper", "GetSubTree", searchPath, 0,
+        ifaceList);
+}
+
+void processSensorConfigs(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& dbusConnection,
+    mctp::MctpRequester& mctpRequester, const ManagedObjectType& resp)
+{
+    for (const auto& [path, interfaces] : resp)
+    {
+        for (const auto& [intf, cfg] : interfaces)
+        {
+            if (intf != configInterfaceName(deviceType))
+            {
+                continue;
+            }
+
+            SensorConfigs configs;
+
+            configs.name = loadVariant<std::string>(cfg, "Name");
+
+            configs.pollRate = loadVariant<uint64_t>(cfg, "PollRate");
+
+            discoverDevices(io, objectServer, gpuDevices, dbusConnection,
+                            mctpRequester, configs, path);
+
+            lg2::info(
+                "Detected configuration {NAME} of type {TYPE} at path: {PATH}.",
+                "NAME", configs.name, "TYPE", deviceType, "PATH", path);
+        }
+    }
+}
+
+void createSensors(
+    boost::asio::io_context& io, sdbusplus::asio::object_server& objectServer,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices,
+    const std::shared_ptr<sdbusplus::asio::connection>& dbusConnection,
+    mctp::MctpRequester& mctpRequester)
+{
+    if (!dbusConnection)
+    {
+        lg2::error("Connection not created");
+        return;
+    }
+    dbusConnection->async_method_call(
+        [&gpuDevices, &mctpRequester, dbusConnection, &io, &objectServer](
+            boost::system::error_code ec, const ManagedObjectType& resp) {
+            if (ec)
+            {
+                lg2::error("Error contacting entity manager");
+                return;
+            }
+
+            processSensorConfigs(io, objectServer, gpuDevices, dbusConnection,
+                                 mctpRequester, resp);
+        },
+        entityManagerName, "/xyz/openbmc_project/inventory",
+        "org.freedesktop.DBus.ObjectManager", "GetManagedObjects");
+}
+
+void interfaceRemoved(
+    sdbusplus::message_t& message,
+    boost::container::flat_map<std::string, std::shared_ptr<GpuDevice>>&
+        gpuDevices)
+{
+    if (message.is_method_error())
+    {
+        lg2::error("interfacesRemoved callback method error");
+        return;
+    }
+
+    sdbusplus::message::object_path removedPath;
+    std::vector<std::string> interfaces;
+
+    message.read(removedPath, interfaces);
+
+    // If the xyz.openbmc_project.Confguration.X interface was removed
+    // for one or more sensors, delete those sensor objects.
+    auto sensorIt = gpuDevices.begin();
+    while (sensorIt != gpuDevices.end())
+    {
+        if ((sensorIt->second->getPath() == removedPath) &&
+            (std::find(interfaces.begin(), interfaces.end(),
+                       configInterfaceName(deviceType)) != interfaces.end()))
+        {
+            sensorIt = gpuDevices.erase(sensorIt);
+        }
+        else
+        {
+            sensorIt++;
+        }
+    }
+}