regulators: Implement i2c_compare_bytes action

Implement the i2c_compare_bytes action in the JSON config file.  See
i2c_compare_bytes.md for more information about this action.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I6997f647a2b899f08f06de43aba62d32f88e1911
diff --git a/phosphor-regulators/src/actions/i2c_compare_bytes_action.cpp b/phosphor-regulators/src/actions/i2c_compare_bytes_action.cpp
new file mode 100644
index 0000000..c7f56f0
--- /dev/null
+++ b/phosphor-regulators/src/actions/i2c_compare_bytes_action.cpp
@@ -0,0 +1,78 @@
+/**
+ * Copyright © 2020 IBM Corporation
+ *
+ * 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 "i2c_compare_bytes_action.hpp"
+
+#include "action_error.hpp"
+#include "i2c_interface.hpp"
+
+#include <exception>
+#include <ios>
+#include <sstream>
+
+namespace phosphor::power::regulators
+{
+
+bool I2CCompareBytesAction::execute(ActionEnvironment& environment)
+{
+    bool isEqual{true};
+    try
+    {
+        // Read actual device register values.  Use I2C mode where the number of
+        // bytes to read is explicitly specified.
+        i2c::I2CInterface& interface = getI2CInterface(environment);
+        uint8_t size = values.size();
+        uint8_t actualValues[UINT8_MAX];
+        interface.read(reg, size, actualValues, i2c::I2CInterface::Mode::I2C);
+
+        // Compare actual byte values to expected byte values
+        for (unsigned int i = 0; i < values.size(); ++i)
+        {
+            if ((actualValues[i] & masks[i]) != values[i])
+            {
+                isEqual = false;
+                break;
+            }
+        }
+    }
+    catch (const i2c::I2CException& e)
+    {
+        // Nest I2CException within an ActionError so caller will have both the
+        // low level I2C error information and the action information
+        std::throw_with_nested(ActionError(*this));
+    }
+    return isEqual;
+}
+
+std::string I2CCompareBytesAction::toString() const
+{
+    std::ostringstream ss;
+    ss << "i2c_compare_bytes: { register: 0x" << std::hex << std::uppercase
+       << static_cast<uint16_t>(reg) << ", values: [ ";
+    for (unsigned int i = 0; i < values.size(); ++i)
+    {
+        ss << ((i > 0) ? ", " : "") << "0x" << static_cast<uint16_t>(values[i]);
+    }
+    ss << " ], masks: [ ";
+    for (unsigned int i = 0; i < masks.size(); ++i)
+    {
+        ss << ((i > 0) ? ", " : "") << "0x" << static_cast<uint16_t>(masks[i]);
+    }
+    ss << " ] }";
+    return ss.str();
+}
+
+} // namespace phosphor::power::regulators