enable softcap and gemma2 (#288)

* enable softcap for gemma2

* fix lint

* restore fa

* restore accidental deletion

* fix logits_soft_cap constructor

* use 0.0 instead of 0

vllm/attention/backends/rocm_flash_attn.py

@@ -459,10 +459,13 @@ def __init__(
         if blocksparse_params is not None:
             raise ValueError(
                 "ROCmFlashAttention does not support blocksparse attention.")
-        if logits_soft_cap is not None:
-            raise ValueError(
-                "ROCmFlashAttention does not support attention logits soft "
-                "capping.")
+
+        if logits_soft_cap is None:
+            # In flash-attn, setting logits_soft_cap as 0 means no soft cap.
+            self.logits_soft_cap = 0.0
+        else:
+            self.logits_soft_cap = logits_soft_cap
+
         self.num_heads = num_heads
         self.head_size = head_size
         self.scale = float(scale)
@@ -487,6 +490,14 @@ def __init__(
         # NOTE: Allow for switching between Triton and CK. Defaulting to triton.
         self.use_triton_flash_attn = envs.VLLM_USE_TRITON_FLASH_ATTN
         if self.use_triton_flash_attn:
+            if logits_soft_cap is not None:
+                raise ValueError(
+                    "ROCm Triton FlashAttention does not support attention"
+                    "logits soft capping."
+                    " please try using the ROCm CK "
+                    "FA backend instead by setting the env var "
+                    "`VLLM_USE_TRITON_FLASH_ATTN=0`")
+
             from vllm.attention.ops.triton_flash_attention import (  # noqa: F401
                 triton_attention)
             self.attn_func = triton_attention
@@ -511,6 +522,11 @@ def __init__(
                     self.use_naive_attn = True
 
             if self.use_naive_attn:
+                if logits_soft_cap is not None:
+                    raise ValueError(
+                        "ROCm Naive FlashAttention does not support"
+                        "attention logits soft capping.")
+
                 self.attn_func = _sdpa_attention
                 logger.debug("Using naive (SDPA) attention in ROCmBackend")
 
@@ -717,6 +733,7 @@ def forward(
                         causal=True,
                         window_size=self.sliding_window,
                         alibi_slopes=self.alibi_slopes,
+                        softcap=self.logits_soft_cap,
                     )
 
                 # common code for prefill