[Bugfix][DeepSeek-V3.2] fix fp8 kvcache type cast (#33884)

Signed-off-by: Kebe <mail@kebe7jun.com>

csrc/cache_kernels.cu

@@ -1234,8 +1234,13 @@ void cp_gather_and_upconvert_fp8_kv_cache(
               "src_cache and seq_lens must be on the same device");
   TORCH_CHECK(src_cache.device() == workspace_starts.device(),
               "src_cache and workspace_starts must be on the same device");
-
-  TORCH_CHECK(src_cache.dtype() == torch::kUInt8, "src_cache must be uint8");
+  auto dtype = src_cache.scalar_type();
+  TORCH_CHECK(
+      dtype == at::ScalarType::Byte ||               // uint8
+          dtype == at::ScalarType::Float8_e4m3fn ||  // fp8 e4m3
+          dtype == at::ScalarType::Float8_e5m2,      // fp8 e5m2
+      "src_cache must be uint8, float8_e4m3fn, or float8_e5m2, but got ",
+      src_cache.dtype());
   TORCH_CHECK(dst.dtype() == torch::kBFloat16, "dst must be bfloat16");
   TORCH_CHECK(head_dim == 576, "head_dim must be 576 for MLA");
 
@@ -1244,14 +1249,21 @@ void cp_gather_and_upconvert_fp8_kv_cache(
   int64_t cache_entry_stride = src_cache.stride(1);
   int64_t dst_entry_stride = dst.stride(0);
 
+  const uint8_t* src_ptr = nullptr;
+  if (dtype == at::ScalarType::Byte) {
+    src_ptr = src_cache.data_ptr<uint8_t>();
+  } else {
+    // float8_e4m3fn or float8_e5m2
+    src_ptr = reinterpret_cast<const uint8_t*>(src_cache.data_ptr());
+  }
+
   // Decide on the number of splits based on the batch size
   int num_splits = batch_size > 128 ? 2 : batch_size > 64 ? 4 : 16;
   dim3 grid(batch_size, num_splits);
   dim3 block(576);
 
   vllm::cp_gather_and_upconvert_fp8_kv_cache<<<grid, block, 0, stream>>>(
-      src_cache.data_ptr<uint8_t>(),
-      reinterpret_cast<__nv_bfloat16*>(dst.data_ptr()),
+      src_ptr, reinterpret_cast<__nv_bfloat16*>(dst.data_ptr()),
       block_table.data_ptr<int32_t>(), seq_lens.data_ptr<int32_t>(),
       workspace_starts.data_ptr<int32_t>(), block_size, head_dim,
       block_table_stride, cache_block_stride, cache_entry_stride,