diff --git a/phosphor-power-supply/test/mock.cpp b/phosphor-power-supply/test/mock.cpp
index a68628b..fc7d658 100644
--- a/phosphor-power-supply/test/mock.cpp
+++ b/phosphor-power-supply/test/mock.cpp
@@ -32,6 +32,11 @@
     util.reset();
 }
 
+std::unique_ptr<GPIOInterface> createGPIO(const std::string& /*namedGpio*/)
+{
+    return std::make_unique<MockedGPIOReader>();
+}
+
 } // namespace psu
 } // namespace power
 } // namespace phosphor
diff --git a/phosphor-power-supply/test/mock.hpp b/phosphor-power-supply/test/mock.hpp
index c1f8986..2731692 100644
--- a/phosphor-power-supply/test/mock.hpp
+++ b/phosphor-power-supply/test/mock.hpp
@@ -3,6 +3,10 @@
 #include "pmbus.hpp"
 #include "util_base.hpp"
 
+#include <gpiod.hpp>
+
+#include <bitset>
+
 #include <gmock/gmock.h>
 
 namespace phosphor
@@ -40,6 +44,16 @@
     MOCK_METHOD(bool, getPresence,
                 (sdbusplus::bus::bus & bus, const std::string& invpath),
                 (const, override));
+    MOCK_METHOD(void, setPresence,
+                (sdbusplus::bus::bus & bus, const std::string& invpath,
+                 bool present, const std::string& name),
+                (const, override));
+};
+
+class MockedGPIOReader : public GPIOInterface
+{
+  public:
+    MOCK_METHOD(int, read, (), (override));
 };
 
 const UtilBase& getUtils();
diff --git a/phosphor-power-supply/test/power_supply_tests.cpp b/phosphor-power-supply/test/power_supply_tests.cpp
index 74d98c1..b298d6c 100644
--- a/phosphor-power-supply/test/power_supply_tests.cpp
+++ b/phosphor-power-supply/test/power_supply_tests.cpp
@@ -20,6 +20,7 @@
 using ::testing::StrEq;
 
 static auto PSUInventoryPath = "/xyz/bmc/inv/sys/chassis/board/powersupply0";
+static auto PSUGPIOLineName = "presence-ps0";
 
 class PowerSupplyTests : public ::testing::Test
 {
@@ -44,13 +45,18 @@
      * @param[in] invpath - String for inventory path to use
      * @param[in] i2cbus - The bus number this power supply is on
      * @param[in] i2caddr - The 16-bit I2C address of the power supply
+     * @param[in] gpioLineName - The string for the gpio-line-name to read for
+     * presence.
+     * @param[in] bindDelay - Time in milliseconds to delay binding the device
+     * driver after seeing the presence line go active.
      */
     auto bus = sdbusplus::bus::new_default();
 
     // Try where inventory path is empty, constructor should fail.
     try
     {
-        auto psu = std::make_unique<PowerSupply>(bus, "", 3, 0x68);
+        auto psu =
+            std::make_unique<PowerSupply>(bus, "", 3, 0x68, PSUGPIOLineName);
         ADD_FAILURE() << "Should not have reached this line.";
     }
     catch (const std::invalid_argument& e)
@@ -62,13 +68,31 @@
         ADD_FAILURE() << "Should not have caught exception.";
     }
 
-    // Test with valid arguments
+    // TODO: Try invalid i2c address?
+
+    // Try where gpioLineName is empty.
     try
     {
-        EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-            .Times(1);
         auto psu =
-            std::make_unique<PowerSupply>(bus, PSUInventoryPath, 3, 0x68);
+            std::make_unique<PowerSupply>(bus, PSUInventoryPath, 3, 0x68, "");
+        ADD_FAILURE()
+            << "Should not have reached this line. Invalid gpioLineName.";
+    }
+    catch (const std::invalid_argument& e)
+    {
+        EXPECT_STREQ(e.what(), "Invalid empty gpioLineName");
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
+
+    // Test with valid arguments
+    // NOT using D-Bus inventory path for presence.
+    try
+    {
+        auto psu = std::make_unique<PowerSupply>(bus, PSUInventoryPath, 3, 0x68,
+                                                 PSUGPIOLineName);
 
         EXPECT_EQ(psu->isPresent(), false);
         EXPECT_EQ(psu->isFaulted(), false);
@@ -80,14 +104,36 @@
     {
         ADD_FAILURE() << "Should not have caught exception.";
     }
+
+    // Test with valid arguments
+    // TODO: Using D-Bus inventory path for presence.
+    try
+    {
+        // FIXME: How do I get that presenceGPIO.read() in the startup to throw
+        // an exception?
+
+        // EXPECT_CALL(mockedUtil, getPresence(_,
+        // StrEq(PSUInventoryPath)))
+        //    .Times(1);
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
 }
 
 TEST_F(PowerSupplyTests, Analyze)
 {
     auto bus = sdbusplus::bus::new_default();
 
-    EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath))).Times(1);
-    PowerSupply psu{bus, PSUInventoryPath, 4, 0x69};
+    // If I default to reading the GPIO, I will NOT expect a call to
+    // getPresence().
+
+    PowerSupply psu{bus, PSUInventoryPath, 4, 0x69, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+    EXPECT_CALL(*mockPresenceGPIO, read()).Times(1).WillOnce(Return(0));
+
     psu.analyze();
     // By default, nothing should change.
     EXPECT_EQ(psu.isPresent(), false);
@@ -96,17 +142,19 @@
     EXPECT_EQ(psu.hasMFRFault(), false);
     EXPECT_EQ(psu.hasVINUVFault(), false);
 
-    // In order to get the various faults tested, the power supply needs to be
-    // present in order to read from the PMBus device(s).
-    EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-        .Times(1)
-        .WillOnce(Return(true)); // present
-    PowerSupply psu2{bus, PSUInventoryPath, 5, 0x6a};
-    EXPECT_EQ(psu2.isPresent(), true);
+    PowerSupply psu2{bus, PSUInventoryPath, 5, 0x6a, PSUGPIOLineName};
+    // In order to get the various faults tested, the power supply needs to
+    // be present in order to read from the PMBus device(s).
+    MockedGPIOReader* mockPresenceGPIO2 =
+        static_cast<MockedGPIOReader*>(psu2.getPresenceGPIO());
+    ON_CALL(*mockPresenceGPIO2, read()).WillByDefault(Return(1));
+
+    EXPECT_EQ(psu2.isPresent(), false);
 
     // STATUS_WORD 0x0000 is powered on, no faults.
+    // It will read STATUS_MFR at the same time, so there are 2 reads.
     MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu2.getPMBus());
-    EXPECT_CALL(mockPMBus, read(_, _)).Times(1).WillOnce(Return(0x0000));
+    EXPECT_CALL(mockPMBus, read(_, _)).Times(2).WillRepeatedly(Return(0x0000));
     psu2.analyze();
     EXPECT_EQ(psu2.isPresent(), true);
     EXPECT_EQ(psu2.isFaulted(), false);
@@ -190,11 +238,14 @@
     // Test where PSU is NOT present
     try
     {
-        EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-            .Times(1)
-            .WillOnce(Return(false));
-        PowerSupply psu{bus, PSUInventoryPath, 4, 0x69};
+        // Assume GPIO presence, not inventory presence?
+        PowerSupply psu{bus, PSUInventoryPath, 4, 0x69, PSUGPIOLineName};
+
+        MockedGPIOReader* mockPresenceGPIO =
+            static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+        ON_CALL(*mockPresenceGPIO, read()).WillByDefault(Return(0));
         MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
+        // Constructor should set initial presence, default read returns 0.
         // If it is not present, I should not be trying to write to it.
         EXPECT_CALL(mockPMBus, writeBinary(_, _, _)).Times(0);
         psu.onOffConfig(data);
@@ -206,11 +257,15 @@
     // Test where PSU is present
     try
     {
-        EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-            .Times(1)
-            .WillOnce(Return(true)); // present
-        PowerSupply psu{bus, PSUInventoryPath, 5, 0x6a};
+        // Assume GPIO presence, not inventory presence?
+        PowerSupply psu{bus, PSUInventoryPath, 5, 0x6a, PSUGPIOLineName};
+        MockedGPIOReader* mockPresenceGPIO =
+            static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+        ON_CALL(*mockPresenceGPIO, read()).WillByDefault(Return(1));
         MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
+        // TODO: expect setPresence call?
+        // updatePresence() private function reads gpio, called by analyze().
+        psu.analyze();
         // TODO: ???should I check the filename?
         EXPECT_CALL(mockPMBus,
                     writeBinary(_, ElementsAre(0x15), Type::HwmonDeviceDebug))
@@ -225,16 +280,19 @@
 TEST_F(PowerSupplyTests, ClearFaults)
 {
     auto bus = sdbusplus::bus::new_default();
-    EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-        .Times(1)
-        .WillOnce(Return(true)); // present
-    PowerSupply psu{bus, PSUInventoryPath, 13, 0x68};
+    PowerSupply psu{bus, PSUInventoryPath, 13, 0x68, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+    // GPIO read return 1 to indicate present.
+    ON_CALL(*mockPresenceGPIO, read()).WillByDefault(Return(1));
+    MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
+    ON_CALL(mockPMBus, read(_, _)).WillByDefault(Return(0));
+    psu.analyze();
     EXPECT_EQ(psu.isPresent(), true);
     EXPECT_EQ(psu.isFaulted(), false);
     EXPECT_EQ(psu.hasInputFault(), false);
     EXPECT_EQ(psu.hasMFRFault(), false);
     EXPECT_EQ(psu.hasVINUVFault(), false);
-    MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
     EXPECT_CALL(mockPMBus, read(_, _))
         .Times(2)
         .WillOnce(Return(0xFFFF))
@@ -254,6 +312,8 @@
     EXPECT_EQ(psu.hasInputFault(), false);
     EXPECT_EQ(psu.hasMFRFault(), false);
     EXPECT_EQ(psu.hasVINUVFault(), false);
+
+    // TODO: Faults clear on missing/present?
 }
 
 TEST_F(PowerSupplyTests, UpdateInventory)
@@ -262,10 +322,7 @@
 
     try
     {
-        EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-            .Times(1)
-            .WillOnce(Return(false)); // missing
-        PowerSupply psu{bus, PSUInventoryPath, 3, 0x68};
+        PowerSupply psu{bus, PSUInventoryPath, 3, 0x68, PSUGPIOLineName};
         MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
         // If it is not present, I should not be trying to read a string
         EXPECT_CALL(mockPMBus, readString(_, _)).Times(0);
@@ -278,10 +335,12 @@
 
     try
     {
-        EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath)))
-            .Times(1)
-            .WillOnce(Return(true)); // present
-        PowerSupply psu{bus, PSUInventoryPath, 13, 0x69};
+        PowerSupply psu{bus, PSUInventoryPath, 13, 0x69, PSUGPIOLineName};
+        MockedGPIOReader* mockPresenceGPIO =
+            static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+        // GPIO read return 1 to indicate present.
+        EXPECT_CALL(*mockPresenceGPIO, read()).Times(1).WillOnce(Return(1));
+        psu.analyze();
         MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
         EXPECT_CALL(mockPMBus, readString(_, _)).WillRepeatedly(Return(""));
         psu.updateInventory();
@@ -307,22 +366,28 @@
 TEST_F(PowerSupplyTests, IsPresent)
 {
     auto bus = sdbusplus::bus::new_default();
-    EXPECT_CALL(mockedUtil, getPresence(_, StrEq(PSUInventoryPath))).Times(1);
-    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68};
+
+    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
     EXPECT_EQ(psu.isPresent(), false);
 
-    EXPECT_CALL(mockedUtil, getPresence(_, _))
-        .WillOnce(Return(true)); // present
-    PowerSupply psu2{bus, PSUInventoryPath, 10, 0x6b};
-    EXPECT_EQ(psu2.isPresent(), true);
+    // Change GPIO read to return 1 to indicate present.
+    EXPECT_CALL(*mockPresenceGPIO, read()).Times(1).WillOnce(Return(1));
+    psu.analyze();
+    EXPECT_EQ(psu.isPresent(), true);
 }
 
 TEST_F(PowerSupplyTests, IsFaulted)
 {
     auto bus = sdbusplus::bus::new_default();
-    EXPECT_CALL(mockedUtil, getPresence(_, _))
-        .WillOnce(Return(true)); // present
-    PowerSupply psu{bus, PSUInventoryPath, 11, 0x6f};
+
+    PowerSupply psu{bus, PSUInventoryPath, 11, 0x6f, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+    // Always return 1 to indicate present.
+    EXPECT_CALL(*mockPresenceGPIO, read()).WillRepeatedly(Return(1));
+    psu.analyze();
     EXPECT_EQ(psu.isFaulted(), false);
     MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
     EXPECT_CALL(mockPMBus, read(_, _))
@@ -336,9 +401,13 @@
 TEST_F(PowerSupplyTests, HasInputFault)
 {
     auto bus = sdbusplus::bus::new_default();
-    EXPECT_CALL(mockedUtil, getPresence(_, _))
-        .WillOnce(Return(true)); // present
-    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68};
+
+    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+    // Always return 1 to indicate present.
+    EXPECT_CALL(*mockPresenceGPIO, read()).WillRepeatedly(Return(1));
+    psu.analyze();
     MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
     EXPECT_EQ(psu.hasInputFault(), false);
     EXPECT_CALL(mockPMBus, read(_, _)).Times(1).WillOnce(Return(0x0000));
@@ -358,9 +427,13 @@
 TEST_F(PowerSupplyTests, HasMFRFault)
 {
     auto bus = sdbusplus::bus::new_default();
-    EXPECT_CALL(mockedUtil, getPresence(_, _))
-        .WillOnce(Return(true)); // present
-    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68};
+
+    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+    // Always return 1 to indicate present.
+    EXPECT_CALL(*mockPresenceGPIO, read()).WillRepeatedly(Return(1));
+    psu.analyze();
     MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
     EXPECT_EQ(psu.hasMFRFault(), false);
     EXPECT_CALL(mockPMBus, read(_, _)).Times(1).WillOnce(Return(0x0000));
@@ -380,9 +453,13 @@
 TEST_F(PowerSupplyTests, HasVINUVFault)
 {
     auto bus = sdbusplus::bus::new_default();
-    EXPECT_CALL(mockedUtil, getPresence(_, _))
-        .WillOnce(Return(true)); // present
-    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68};
+
+    PowerSupply psu{bus, PSUInventoryPath, 3, 0x68, PSUGPIOLineName};
+    MockedGPIOReader* mockPresenceGPIO =
+        static_cast<MockedGPIOReader*>(psu.getPresenceGPIO());
+    // Always return 1 to indicate present.
+    EXPECT_CALL(*mockPresenceGPIO, read()).WillRepeatedly(Return(1));
+    psu.analyze();
     MockedPMBus& mockPMBus = static_cast<MockedPMBus&>(psu.getPMBus());
     EXPECT_EQ(psu.hasVINUVFault(), false);
     EXPECT_CALL(mockPMBus, read(_, _)).Times(1).WillOnce(Return(0x0000));