Improve CPU mask creation utility to consider higher ids first (#210)

---
Signed-off-by: Kartik Nema <kartnema@qti.qualcomm.com>

Author: kartnema

modula/CoreModules/AuxRoutines.cpp

@@ -89,6 +89,10 @@ int8_t AuxRoutines::fileExists(const std::string& filePath) {
     return access(filePath.c_str(), F_OK) == 0;
 }
 
+int8_t AuxRoutines::fileWritable(const std::string& filePath) {
+    return access(filePath.c_str(), W_OK) == 0;
+}
+
 std::string AuxRoutines::getMachineName() {
     return AuxRoutines::readFromFile(UrmSettings::mDeviceNamePath);
 }

modula/CoreModules/Include/AuxRoutines.h

@@ -32,6 +32,7 @@ class AuxRoutines {
     static void deleteFile(const std::string& fileName);
     static void writeSysFsDefaults();
     static int8_t fileExists(const std::string& filePath);
+    static int8_t fileWritable(const std::string& filePath);
     static std::string getMachineName();
 
     static int8_t isNumericString(const std::string& str);

resource-tuner/core/TargetRegistry.cpp

@@ -824,37 +824,68 @@ uint64_t GET_TARGET_INFO(int32_t option,
     std::shared_ptr<TargetRegistry> targetRegistry = TargetRegistry::getInstance();
 
     switch(option) {
+        // Returns a 64-bit mask, encodes cpu ids in the range [0, 63]
+        // By default mask creation begins at the lowest core within the cluster
+        // and goes up one at a time to core: (start + min(numCpus, coreCount)).
+        // Where numCpus is the total count of cpus in the specified cluster.
+
+        // Reverse selection is also possible, if a negative coreCount is provided
+        // Whereby the highest abs(coreCount) cpu ids within the cluster are considered
+        // for mask generation.
         case GET_MASK: {
             if(numArgs < 2) {
                 return 0;
             }
 
             uint64_t mask = 0;
-
             int32_t cluster = args[0];
             int32_t coreCount = args[1];
 
             if(cluster == GET_MAX_CLUSTER) {
-                int32_t clusterCount = UrmSettings::targetConfigs.mTotalClusterCount;
-                cluster = clusterCount - 1;
+                cluster = UrmSettings::targetConfigs.mTotalClusterCount - 1;
             }
 
             int32_t physicalClusterId = targetRegistry->getPhysicalClusterId(cluster);
             ClusterInfo* clusInfo = targetRegistry->getClusterInfo(physicalClusterId);
-            if(clusInfo == nullptr) {
+            if(clusInfo == nullptr || clusInfo->mNumCpus <= 0) {
                 return 0;
             }
 
+            int8_t generateReverseMask = false;
             if(coreCount == 0) {
                 // Iterate over all the cores in the cluster
                 coreCount = clusInfo->mNumCpus;
             } else {
+                if(coreCount < 0) {
+                    // Sanity Check
+                    if(coreCount == std::numeric_limits<int32_t>::min()) {
+                        return 0;
+                    }
+
+                    coreCount *= -1;
+                    generateReverseMask = true;
+                }
+
                 // Bound the count to the number of cores in the cluster
                 coreCount = std::min(coreCount, clusInfo->mNumCpus);
             }
 
-            for(int32_t i = clusInfo->mStartCpu; i < (clusInfo->mStartCpu + coreCount); i++) {
-                mask |= (1UL << i);
+            int32_t curCpu = clusInfo->mStartCpu;
+            if(generateReverseMask) {
+                curCpu = clusInfo->mStartCpu + clusInfo->mNumCpus - 1;
+                while(coreCount--) {
+                    if(curCpu >= 0 && curCpu < 64) {
+                        mask |= (1ULL << curCpu);
+                    }
+                    curCpu--;
+                }
+            } else {
+                while(coreCount--) {
+                    if(curCpu >= 0 && curCpu < 64) {
+                        mask |= (1ULL << curCpu);
+                    }
+                    curCpu++;
+                }
             }
 
             return mask;

tests/Component/ExtensionIntfTests.cpp

@@ -1,10 +1,10 @@
 // Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
 // SPDX-License-Identifier: BSD-3-Clause-Clear
 
+#include "URMTests.h"
 #include "TestUtils.h"
-#include "ResourceRegistry.h"
 #include "RestuneParser.h"
-#include "URMTests.h"
+#include "ResourceRegistry.h"
 
 #define TEST_CLASS "COMPONENT"
 #define TEST_SUBCAT "1_URM_EXTN_INTF"