nvidia-gpu: add support for communication to the endpoint

The commit uses MCTP VDM protocol to read temperature sensor value from
the gpu.

The MCTP VDM protocol is an extension of the OCP Accelerator Management
Interface specification. [1]

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

Restart the nvidiagpusensor service.
```
root@gb200nvl-obmc:~# systemctl start xyz.openbmc_project.nvidiagpusensor.service
```

The app is detecting entity-manager configuration on gb200nvl-obmc
machine. The app is also able to detect all the endpoints from the mctp
service dbus tree. The app is reading temperature sensor value from gpu
correctly and the temperature sensor is also present on redfish.

```
$ curl -k -u 'root:0penBmc' https://10.137.203.137/redfish/v1/Chassis/NVIDIA_GB200_1/Sensors/temperature_NVIDIA_GB200_GPU
{
  "@odata.id": "/redfish/v1/Chassis/NVIDIA_GB200_1/Sensors/temperature_NVIDIA_GB200_GPU",
  "@odata.type": "#Sensor.v1_2_0.Sensor",
  "Id": "temperature_NVIDIA_GB200_GPU",
  "Name": "NVIDIA GB200 GPU",
  "Reading": 36.4375,
  "ReadingRangeMax": 127.0,
  "ReadingRangeMin": -128.0,
  "ReadingType": "Temperature",
  "ReadingUnits": "Cel",
  "Status": {
    "Health": "OK",
    "State": "Enabled"
  }
}%

root@gb200nvl-obmc:~# busctl tree xyz.openbmc_project.GpuSensor
└─ /xyz
  └─ /xyz/openbmc_project
    └─ /xyz/openbmc_project/sensors
      └─ /xyz/openbmc_project/sensors/temperature
        └─ /xyz/openbmc_project/sensors/temperature/NVIDIA_GB200_GPU

root@gb200nvl-obmc:~# busctl introspect xyz.openbmc_project.GpuSensor /xyz/openbmc_project/sensors/temperature/NVIDIA_GB200_GPU
NAME                                                  TYPE      SIGNATURE RESULT/VALUE                             FLAGS
org.freedesktop.DBus.Introspectable                   interface -         -                                        -
.Introspect                                           method    -         s                                        -
org.freedesktop.DBus.Peer                             interface -         -                                        -
.GetMachineId                                         method    -         s                                        -
.Ping                                                 method    -         -                                        -
org.freedesktop.DBus.Properties                       interface -         -                                        -
.Get                                                  method    ss        v                                        -
.GetAll                                               method    s         a{sv}                                    -
.Set                                                  method    ssv       -                                        -
.PropertiesChanged                                    signal    sa{sv}as  -                                        -
xyz.openbmc_project.Association.Definitions           interface -         -                                        -
.Associations                                         property  a(sss)    1 "chassis" "all_sensors" "/xyz/openbmc… emits-change
xyz.openbmc_project.Sensor.Value                      interface -         -                                        -
.MaxValue                                             property  d         127                                      emits-change
.MinValue                                             property  d         -128                                     emits-change
.Unit                                                 property  s         "xyz.openbmc_project.Sensor.Value.Unit.… emits-change
.Value                                                property  d         36.3125                                  emits-change writable
xyz.openbmc_project.Sensor.ValueMutability            interface -         -                                        -
.Mutable                                              property  b         true                                     emits-change
xyz.openbmc_project.State.Decorator.Availability      interface -         -                                        -
.Available                                            property  b         true                                     emits-change writable
xyz.openbmc_project.State.Decorator.OperationalStatus interface -         -                                        -
.Functional                                           property  b         true                                     emits-change
```

[1] https://www.opencompute.org/documents/ocp-gpu-accelerator-management-interfaces-v1-pdf

Change-Id: Ied938b9e5c19751ee283b4b948e16c905c78fb48
Signed-off-by: Harshit Aghera <haghera@nvidia.com>
diff --git a/src/nvidia-gpu/tests/NvidiaGpuSensorTest.cpp b/src/nvidia-gpu/tests/NvidiaGpuSensorTest.cpp
new file mode 100644
index 0000000..c630ffa
--- /dev/null
+++ b/src/nvidia-gpu/tests/NvidiaGpuSensorTest.cpp
@@ -0,0 +1,500 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION &
+ * AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "NvidiaGpuMctpVdm.hpp"
+#include "OcpMctpVdm.hpp"
+
+#include <endian.h>
+
+#include <array>
+#include <cerrno>
+#include <cstdint>
+#include <cstring>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+namespace ocp_mctp_tests
+{
+
+class OcpMctpVdmTests : public ::testing::Test
+{
+  protected:
+    void SetUp() override
+    {
+        // Initialize common test data here
+    }
+};
+
+// Tests for OcpMctpVdm::packHeader function
+TEST_F(OcpMctpVdmTests, PackHeaderRequestSuccess)
+{
+    const uint16_t pciVendorId = 0x1234;
+    ocp::accelerator_management::BindingPciVidInfo hdr{};
+    ocp::accelerator_management::BindingPciVid msg{};
+
+    hdr.ocp_accelerator_management_msg_type =
+        static_cast<uint8_t>(ocp::accelerator_management::MessageType::REQUEST);
+    hdr.instance_id = 5;
+    hdr.msg_type = 0x7E;
+
+    int result = ocp::accelerator_management::packHeader(pciVendorId, hdr, msg);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(msg.pci_vendor_id, htobe16(pciVendorId));
+    EXPECT_EQ(msg.instance_id & ocp::accelerator_management::instanceIdBitMask,
+              5);
+    EXPECT_NE(msg.instance_id & ocp::accelerator_management::requestBitMask, 0);
+    EXPECT_EQ(msg.ocp_version & 0x0F, ocp::accelerator_management::ocpVersion);
+    EXPECT_EQ((msg.ocp_version & 0xF0) >>
+                  ocp::accelerator_management::ocpTypeBitOffset,
+              ocp::accelerator_management::ocpType);
+    EXPECT_EQ(msg.ocp_accelerator_management_msg_type, 0x7E);
+}
+
+TEST_F(OcpMctpVdmTests, PackHeaderResponseSuccess)
+{
+    const uint16_t pciVendorId = 0x1234;
+    ocp::accelerator_management::BindingPciVidInfo hdr{};
+    ocp::accelerator_management::BindingPciVid msg{};
+
+    hdr.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    hdr.instance_id = 10;
+    hdr.msg_type = 0x7E;
+
+    int result = ocp::accelerator_management::packHeader(pciVendorId, hdr, msg);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(msg.pci_vendor_id, htobe16(pciVendorId));
+    EXPECT_EQ(msg.instance_id & ocp::accelerator_management::instanceIdBitMask,
+              10);
+    EXPECT_EQ(msg.instance_id & ocp::accelerator_management::requestBitMask, 0);
+    EXPECT_EQ(msg.ocp_version & 0x0F, ocp::accelerator_management::ocpVersion);
+    EXPECT_EQ((msg.ocp_version & 0xF0) >>
+                  ocp::accelerator_management::ocpTypeBitOffset,
+              ocp::accelerator_management::ocpType);
+    EXPECT_EQ(msg.ocp_accelerator_management_msg_type, 0x7E);
+}
+
+TEST_F(OcpMctpVdmTests, PackHeaderInvalidMessageType)
+{
+    const uint16_t pciVendorId = 0x1234;
+    ocp::accelerator_management::BindingPciVidInfo hdr{};
+    ocp::accelerator_management::BindingPciVid msg{};
+
+    hdr.ocp_accelerator_management_msg_type = 3; // Invalid message type
+    hdr.instance_id = 5;
+    hdr.msg_type = 0x7E;
+
+    int result = ocp::accelerator_management::packHeader(pciVendorId, hdr, msg);
+
+    EXPECT_EQ(result, EINVAL);
+}
+
+TEST_F(OcpMctpVdmTests, PackHeaderInvalidInstanceId)
+{
+    const uint16_t pciVendorId = 0x1234;
+    ocp::accelerator_management::BindingPciVidInfo hdr{};
+    ocp::accelerator_management::BindingPciVid msg{};
+
+    hdr.ocp_accelerator_management_msg_type =
+        static_cast<uint8_t>(ocp::accelerator_management::MessageType::REQUEST);
+    hdr.instance_id = 32; // Out of range (0-31 valid)
+    hdr.msg_type = 0x7E;
+
+    int result = ocp::accelerator_management::packHeader(pciVendorId, hdr, msg);
+
+    EXPECT_EQ(result, EINVAL);
+}
+
+// Tests for OcpMctpVdm::decodeReasonCodeAndCC function
+TEST_F(OcpMctpVdmTests, DecodeReasonCodeAndCCSuccessCase)
+{
+    ocp::accelerator_management::CommonNonSuccessResponse response{};
+    response.command = 0x42;
+    response.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::SUCCESS);
+    response.reason_code = htole16(0x1234);
+
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+
+    std::array<uint8_t, sizeof(response)> buf{};
+    std::memcpy(buf.data(), &response, sizeof(response));
+
+    int result =
+        ocp::accelerator_management::decodeReasonCodeAndCC(buf, cc, reasonCode);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(cc, ocp::accelerator_management::CompletionCode::SUCCESS);
+    EXPECT_EQ(reasonCode, 0); // Should be 0 for SUCCESS
+}
+
+TEST_F(OcpMctpVdmTests, DecodeReasonCodeAndCCErrorCase)
+{
+    ocp::accelerator_management::CommonNonSuccessResponse response{};
+    response.command = 0x42;
+    response.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::ERROR);
+    response.reason_code = htole16(0x5678);
+
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+
+    std::array<uint8_t, sizeof(response)> buf{};
+    std::memcpy(buf.data(), &response, sizeof(response));
+
+    int result =
+        ocp::accelerator_management::decodeReasonCodeAndCC(buf, cc, reasonCode);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(cc, ocp::accelerator_management::CompletionCode::ERROR);
+    EXPECT_EQ(reasonCode, 0x5678);
+}
+
+} // namespace ocp_mctp_tests
+
+namespace gpu_mctp_tests
+{
+
+class GpuMctpVdmTests : public ::testing::Test
+{
+  protected:
+    void SetUp() override
+    {
+        // Initialize common test data here
+    }
+};
+
+// Tests for GpuMctpVdm::packHeader function
+TEST_F(GpuMctpVdmTests, PackHeaderSuccess)
+{
+    ocp::accelerator_management::BindingPciVidInfo hdr{};
+    ocp::accelerator_management::BindingPciVid msg{};
+
+    hdr.ocp_accelerator_management_msg_type =
+        static_cast<uint8_t>(ocp::accelerator_management::MessageType::REQUEST);
+    hdr.instance_id = 5;
+    hdr.msg_type = 0x7E;
+
+    int result = gpu::packHeader(hdr, msg);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(msg.pci_vendor_id, htobe16(gpu::nvidiaPciVendorId));
+    EXPECT_EQ(msg.instance_id & ocp::accelerator_management::instanceIdBitMask,
+              5);
+    EXPECT_NE(msg.instance_id & ocp::accelerator_management::requestBitMask, 0);
+    EXPECT_EQ(msg.ocp_version & 0x0F, ocp::accelerator_management::ocpVersion);
+    EXPECT_EQ((msg.ocp_version & 0xF0) >>
+                  ocp::accelerator_management::ocpTypeBitOffset,
+              ocp::accelerator_management::ocpType);
+    EXPECT_EQ(msg.ocp_accelerator_management_msg_type, 0x7E);
+}
+
+// Tests for GpuMctpVdm::encodeQueryDeviceIdentificationRequest function
+TEST_F(GpuMctpVdmTests, EncodeQueryDeviceIdentificationRequestSuccess)
+{
+    const uint8_t instanceId = 3;
+    std::vector<uint8_t> buf(256);
+
+    int result = gpu::encodeQueryDeviceIdentificationRequest(instanceId, buf);
+
+    EXPECT_EQ(result, 0);
+
+    gpu::QueryDeviceIdentificationRequest request{};
+    std::memcpy(&request, buf.data(), sizeof(request));
+
+    EXPECT_EQ(request.hdr.msgHdr.hdr.pci_vendor_id,
+              htobe16(gpu::nvidiaPciVendorId));
+    EXPECT_EQ(request.hdr.msgHdr.hdr.instance_id &
+                  ocp::accelerator_management::instanceIdBitMask,
+              instanceId & ocp::accelerator_management::instanceIdBitMask);
+    EXPECT_NE(request.hdr.msgHdr.hdr.instance_id &
+                  ocp::accelerator_management::requestBitMask,
+              0);
+
+    EXPECT_EQ(request.hdr.command,
+              static_cast<uint8_t>(gpu::DeviceCapabilityDiscoveryCommands::
+                                       QUERY_DEVICE_IDENTIFICATION));
+    EXPECT_EQ(request.hdr.data_size, 0);
+}
+
+// Tests for GpuMctpVdm::decodeQueryDeviceIdentificationResponse function
+TEST_F(GpuMctpVdmTests, DecodeQueryDeviceIdentificationResponseSuccess)
+{
+    // Create a mock successful response
+    std::vector<uint8_t> buf(sizeof(gpu::QueryDeviceIdentificationResponse));
+
+    gpu::QueryDeviceIdentificationResponse response{};
+    ocp::accelerator_management::BindingPciVidInfo headerInfo{};
+    headerInfo.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    headerInfo.instance_id = 3;
+    headerInfo.msg_type =
+        static_cast<uint8_t>(gpu::MessageType::DEVICE_CAPABILITY_DISCOVERY);
+
+    gpu::packHeader(headerInfo, response.hdr.msgHdr.hdr);
+
+    // Populate response data
+    response.hdr.command = static_cast<uint8_t>(
+        gpu::DeviceCapabilityDiscoveryCommands::QUERY_DEVICE_IDENTIFICATION);
+    response.hdr.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::SUCCESS);
+    response.hdr.reserved = 0;
+    response.hdr.data_size =
+        htole16(2); // Size of device_identification + instance_id
+    response.device_identification =
+        static_cast<uint8_t>(gpu::DeviceIdentification::DEVICE_GPU);
+    response.instance_id = 7;
+
+    std::memcpy(buf.data(), &response, sizeof(response));
+
+    // Test decoding
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+    uint8_t deviceIdentification{};
+    uint8_t deviceInstance{};
+
+    int result = gpu::decodeQueryDeviceIdentificationResponse(
+        buf, cc, reasonCode, deviceIdentification, deviceInstance);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(cc, ocp::accelerator_management::CompletionCode::SUCCESS);
+    EXPECT_EQ(reasonCode, 0);
+    EXPECT_EQ(deviceIdentification,
+              static_cast<uint8_t>(gpu::DeviceIdentification::DEVICE_GPU));
+    EXPECT_EQ(deviceInstance, 7);
+}
+
+TEST_F(GpuMctpVdmTests, DecodeQueryDeviceIdentificationResponseError)
+{
+    // Create a mock successful response
+    std::vector<uint8_t> buf(
+        sizeof(ocp::accelerator_management::CommonNonSuccessResponse));
+
+    ocp::accelerator_management::CommonNonSuccessResponse response{};
+    ocp::accelerator_management::BindingPciVidInfo headerInfo{};
+    headerInfo.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    headerInfo.instance_id = 3;
+    headerInfo.msg_type =
+        static_cast<uint8_t>(gpu::MessageType::DEVICE_CAPABILITY_DISCOVERY);
+
+    gpu::packHeader(headerInfo, response.msgHdr.hdr);
+
+    // Populate response data
+    response.command = static_cast<uint8_t>(
+        gpu::DeviceCapabilityDiscoveryCommands::QUERY_DEVICE_IDENTIFICATION);
+    response.command = static_cast<uint8_t>(
+        gpu::DeviceCapabilityDiscoveryCommands::QUERY_DEVICE_IDENTIFICATION);
+    response.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::ERROR);
+    response.reason_code = htole16(0x1234);
+
+    std::memcpy(buf.data(), &response, sizeof(response));
+
+    // Test decoding
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+    uint8_t deviceIdentification{};
+    uint8_t deviceInstance{};
+
+    int result = gpu::decodeQueryDeviceIdentificationResponse(
+        buf, cc, reasonCode, deviceIdentification, deviceInstance);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(cc, ocp::accelerator_management::CompletionCode::ERROR);
+    EXPECT_EQ(reasonCode, 0x1234);
+}
+
+TEST_F(GpuMctpVdmTests, DecodeQueryDeviceIdentificationResponseInvalidSize)
+{
+    // Create a too-small buffer
+    std::vector<uint8_t> buf(
+        sizeof(ocp::accelerator_management::Message) + 2); // Too small
+
+    // Populate Message header only
+    ocp::accelerator_management::Message msg{};
+    ocp::accelerator_management::BindingPciVidInfo headerInfo{};
+    headerInfo.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    headerInfo.instance_id = 3;
+    headerInfo.msg_type =
+        static_cast<uint8_t>(gpu::MessageType::DEVICE_CAPABILITY_DISCOVERY);
+
+    gpu::packHeader(headerInfo, msg.hdr);
+    std::memcpy(buf.data(), &msg, sizeof(msg));
+
+    // Test decoding with insufficient data
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+    uint8_t deviceIdentification{};
+    uint8_t deviceInstance{};
+
+    int result = gpu::decodeQueryDeviceIdentificationResponse(
+        buf, cc, reasonCode, deviceIdentification, deviceInstance);
+
+    EXPECT_EQ(result, EINVAL); // Should indicate error for invalid size
+}
+
+// Tests for GpuMctpVdm::encodeGetTemperatureReadingRequest function
+TEST_F(GpuMctpVdmTests, EncodeGetTemperatureReadingRequestSuccess)
+{
+    const uint8_t instanceId = 4;
+    const uint8_t sensorId = 0;
+    std::vector<uint8_t> buf(256);
+
+    int result =
+        gpu::encodeGetTemperatureReadingRequest(instanceId, sensorId, buf);
+
+    EXPECT_EQ(result, 0);
+
+    gpu::GetTemperatureReadingRequest request{};
+    std::memcpy(&request, buf.data(), sizeof(request));
+
+    EXPECT_EQ(request.hdr.msgHdr.hdr.pci_vendor_id,
+              htobe16(gpu::nvidiaPciVendorId));
+    EXPECT_EQ(request.hdr.msgHdr.hdr.instance_id &
+                  ocp::accelerator_management::instanceIdBitMask,
+              instanceId & ocp::accelerator_management::instanceIdBitMask);
+    EXPECT_NE(request.hdr.msgHdr.hdr.instance_id &
+                  ocp::accelerator_management::requestBitMask,
+              0);
+    EXPECT_EQ(request.hdr.msgHdr.hdr.ocp_accelerator_management_msg_type,
+              static_cast<uint8_t>(gpu::MessageType::PLATFORM_ENVIRONMENTAL));
+
+    // Verify request data
+    EXPECT_EQ(request.hdr.command,
+              static_cast<uint8_t>(
+                  gpu::PlatformEnvironmentalCommands::GET_TEMPERATURE_READING));
+    EXPECT_EQ(request.hdr.data_size, sizeof(sensorId));
+    EXPECT_EQ(request.sensor_id, sensorId);
+}
+
+// Tests for GpuMctpVdm::decodeGetTemperatureReadingResponse function
+TEST_F(GpuMctpVdmTests, DecodeGetTemperatureReadingResponseSuccess)
+{
+    // Create a mock successful response
+    std::vector<uint8_t> buf(sizeof(gpu::GetTemperatureReadingResponse));
+
+    gpu::GetTemperatureReadingResponse response{};
+    ocp::accelerator_management::BindingPciVidInfo headerInfo{};
+    headerInfo.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    headerInfo.instance_id = 4;
+    headerInfo.msg_type =
+        static_cast<uint8_t>(gpu::MessageType::PLATFORM_ENVIRONMENTAL);
+
+    gpu::packHeader(headerInfo, response.hdr.msgHdr.hdr);
+
+    // Populate response data
+    response.hdr.command = static_cast<uint8_t>(
+        gpu::PlatformEnvironmentalCommands::GET_TEMPERATURE_READING);
+    response.hdr.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::SUCCESS);
+    response.hdr.reserved = 0;
+    response.hdr.data_size = htole16(sizeof(int32_t));
+
+    // Set a temperature value of 75.5°C (75.5 * 256 = 19328)
+    response.reading = htole32(19328);
+
+    std::memcpy(buf.data(), &response, sizeof(response));
+
+    // Test decoding
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+    double temperatureReading{};
+
+    int result = gpu::decodeGetTemperatureReadingResponse(
+        buf, cc, reasonCode, temperatureReading);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(cc, ocp::accelerator_management::CompletionCode::SUCCESS);
+    EXPECT_EQ(reasonCode, 0);
+    EXPECT_NEAR(temperatureReading, 75.5, 0.01);
+}
+
+TEST_F(GpuMctpVdmTests, DecodeGetTemperatureReadingResponseError)
+{
+    std::vector<uint8_t> buf(
+        sizeof(ocp::accelerator_management::CommonNonSuccessResponse));
+
+    // Populate error response data
+    ocp::accelerator_management::CommonNonSuccessResponse errorResponse{};
+    ocp::accelerator_management::BindingPciVidInfo headerInfo{};
+    headerInfo.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    headerInfo.instance_id = 3;
+    headerInfo.msg_type =
+        static_cast<uint8_t>(gpu::MessageType::DEVICE_CAPABILITY_DISCOVERY);
+
+    gpu::packHeader(headerInfo, errorResponse.msgHdr.hdr);
+
+    errorResponse.command = static_cast<uint8_t>(
+        gpu::PlatformEnvironmentalCommands::GET_TEMPERATURE_READING);
+    errorResponse.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::ERR_NOT_READY);
+    errorResponse.reason_code = htole16(0x4321);
+
+    std::memcpy(buf.data(), &errorResponse, sizeof(errorResponse));
+
+    // Test decoding
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+    double temperatureReading{};
+
+    int result = gpu::decodeGetTemperatureReadingResponse(
+        buf, cc, reasonCode, temperatureReading);
+
+    EXPECT_EQ(result, 0);
+    EXPECT_EQ(cc, ocp::accelerator_management::CompletionCode::ERR_NOT_READY);
+    EXPECT_EQ(reasonCode, 0x4321);
+}
+
+TEST_F(GpuMctpVdmTests, DecodeGetTemperatureReadingResponseInvalidSize)
+{
+    // Create a mock response with invalid data_size
+    std::vector<uint8_t> buf(sizeof(gpu::GetTemperatureReadingResponse));
+
+    gpu::GetTemperatureReadingResponse response{};
+    ocp::accelerator_management::BindingPciVidInfo headerInfo{};
+    headerInfo.ocp_accelerator_management_msg_type = static_cast<uint8_t>(
+        ocp::accelerator_management::MessageType::RESPONSE);
+    headerInfo.instance_id = 4;
+    headerInfo.msg_type =
+        static_cast<uint8_t>(gpu::MessageType::PLATFORM_ENVIRONMENTAL);
+
+    gpu::packHeader(headerInfo, response.hdr.msgHdr.hdr);
+
+    response.hdr.command = static_cast<uint8_t>(
+        gpu::PlatformEnvironmentalCommands::GET_TEMPERATURE_READING);
+    response.hdr.completion_code = static_cast<uint8_t>(
+        ocp::accelerator_management::CompletionCode::SUCCESS);
+    response.hdr.reserved = 0;
+    response.hdr.data_size = htole16(1); // Invalid - should be sizeof(int32_t)
+    response.reading = htole32(19328);
+
+    std::memcpy(buf.data(), &response, sizeof(response));
+
+    // Test decoding
+    ocp::accelerator_management::CompletionCode cc{};
+    uint16_t reasonCode{};
+    double temperatureReading{};
+
+    int result = gpu::decodeGetTemperatureReadingResponse(
+        buf, cc, reasonCode, temperatureReading);
+
+    EXPECT_EQ(result, EINVAL); // Should indicate error for invalid data size
+}
+
+} // namespace gpu_mctp_tests
+
+int main(int argc, char** argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}
diff --git a/src/nvidia-gpu/tests/meson.build b/src/nvidia-gpu/tests/meson.build
new file mode 100644
index 0000000..4923868
--- /dev/null
+++ b/src/nvidia-gpu/tests/meson.build
@@ -0,0 +1,29 @@
+gtest_dep = dependency('gtest', main: true, disabler: true, required: false)
+gmock_dep = dependency('gmock', disabler: true, required: false)
+if not gtest_dep.found() or not gmock_dep.found()
+    gtest_proj = import('cmake').subproject('googletest', required: true)
+    gtest_dep = declare_dependency(
+        dependencies: [
+            dependency('threads'),
+            gtest_proj.dependency('gtest'),
+            gtest_proj.dependency('gtest_main'),
+        ],
+    )
+    gmock_dep = gtest_proj.dependency('gmock')
+endif
+
+gpusensor_test_include_dirs = [gpusensor_include_dir]
+
+test(
+    'nvidiagpusensor_test',
+    executable(
+        'nvidiagpusensor_test',
+        'NvidiaGpuSensorTest.cpp',
+        '../OcpMctpVdm.cpp',
+        '../NvidiaGpuMctpVdm.cpp',
+        implicit_include_directories: false,
+        include_directories: gpusensor_test_include_dirs,
+        dependencies: [gtest_dep, gmock_dep],
+    ),
+    workdir: meson.current_source_dir(),
+)