simple align qwen2vl kv_seq_len calculation with qwen2

src/transformers/models/qwen2_vl/modeling_qwen2_vl.py

@@ -550,8 +550,13 @@ def forward(
 
         kv_seq_len = key_states.shape[-2]
         if past_key_value is not None:
-            kv_seq_len += cache_position[0] + 1
-
+            if self.layer_idx is None:
+                raise ValueError(
+                    f"The cache structure has changed since version v4.36. If you are using {self.__class__.__name__} "
+                    "for auto-regressive decoding with k/v caching, please make sure to initialize the attention class "
+                    "with a layer index."
+                )
+            kv_seq_len += past_key_value.get_usable_length(kv_seq_len, self.layer_idx)
         cos, sin = self.rotary_emb(value_states, seq_len=kv_seq_len)
         query_states, key_states = apply_multimodal_rotary_pos_emb(
             query_states, key_states, cos, sin, position_ids, self.rope_scaling["mrope_section"]
@@ -632,10 +637,19 @@ def forward(
 
         kv_seq_len = key_states.shape[-2]
         if past_key_value is not None:
-            kv_seq_len += cache_position[0] + 1
+            if self.layer_idx is None:
+                raise ValueError(
+                    f"The cache structure has changed since version v4.36. If you are using {self.__class__.__name__} "
+                    "for auto-regressive decoding with k/v caching, please make sure to initialize the attention class "
+                    "with a layer index."
+                )
+            kv_seq_len += past_key_value.get_usable_length(kv_seq_len, self.layer_idx)
 
         # Because the input can be padded, the absolute sequence length depends on the max position id.
-        rotary_seq_len = cache_position[-1]
+        rotary_seq_len = (
+            max(kv_seq_len, position_ids[:, -1].max().item() + 1) if position_ids is not None else kv_seq_len
+        )
+
         cos, sin = self.rotary_emb(value_states, seq_len=rotary_seq_len)
 
         query_states, key_states = apply_multimodal_rotary_pos_emb(