Add restrictions on usages allowed with MapRead/Write

src/backend/common/Buffer.cpp

@@ -188,12 +188,25 @@ namespace backend {
             return nullptr;
         }
 
+        const nxt::BufferUsageBit kMapWriteAllowedUsages = nxt::BufferUsageBit::MapWrite | nxt::BufferUsageBit::TransferSrc;
+        if (allowedUsage & nxt::BufferUsageBit::MapWrite &&
+            (allowedUsage & kMapWriteAllowedUsages) != allowedUsage) {
+            HandleError("Only TransferSrc is allowed with MapWrite");
+            return nullptr;
+        }
+
+        const nxt::BufferUsageBit kMapReadAllowedUsages = nxt::BufferUsageBit::MapRead | nxt::BufferUsageBit::TransferDst;
+        if (allowedUsage & nxt::BufferUsageBit::MapRead &&
+            (allowedUsage & kMapReadAllowedUsages) != allowedUsage) {
+            HandleError("Only TransferDst is allowed with MapRead");
+            return nullptr;
+        }
+
         if (!BufferBase::IsUsagePossible(allowedUsage, currentUsage)) {
             HandleError("Initial buffer usage is not allowed");
             return nullptr;
         }
 
-        // TODO(cwallez@chromium.org) disallow using MapRead with anything else than TransferDst
         return device->CreateBuffer(this);
     }
 

src/tests/unittests/validation/BufferValidationTests.cpp

@@ -142,6 +142,41 @@ TEST_F(BufferValidationTest, CreationMissingProperties) {
     }
 }
 
+// Test restriction on usages allowed with MapRead and MapWrite
+TEST_F(BufferValidationTest, CreationMapUsageRestrictions) {
+    // MapRead with TransferDst is ok
+    {
+        nxt::Buffer buf = AssertWillBeSuccess(device.CreateBufferBuilder(), "1")
+            .SetAllowedUsage(nxt::BufferUsageBit::MapRead | nxt::BufferUsageBit::TransferDst)
+            .SetSize(4)
+            .GetResult();
+    }
+
+    // MapRead with something else is an error
+    {
+        nxt::Buffer buf = AssertWillBeError(device.CreateBufferBuilder(), "2")
+            .SetAllowedUsage(nxt::BufferUsageBit::MapRead | nxt::BufferUsageBit::Uniform)
+            .SetSize(4)
+            .GetResult();
+    }
+
+    // MapWrite with TransferSrc is ok
+    {
+        nxt::Buffer buf = AssertWillBeSuccess(device.CreateBufferBuilder(), "3")
+            .SetAllowedUsage(nxt::BufferUsageBit::MapWrite | nxt::BufferUsageBit::TransferSrc)
+            .SetSize(4)
+            .GetResult();
+    }
+
+    // MapWrite with something else is an error
+    {
+        nxt::Buffer buf = AssertWillBeError(device.CreateBufferBuilder(), "4")
+            .SetAllowedUsage(nxt::BufferUsageBit::MapWrite | nxt::BufferUsageBit::Uniform)
+            .SetSize(4)
+            .GetResult();
+    }
+}
+
 // Test the success cause for mapping buffer for reading
 TEST_F(BufferValidationTest, MapReadSuccess) {
     nxt::Buffer buf = CreateMapReadBuffer(4);