Fix Flax flip_sin_to_cos (#1369)

* Fix Flax flip_sin_to_cos

* Adding flip_sin_to_cos
Co-authored-by: Kashif Rasul <kashif.rasul@gmail.com>

src/diffusers/models/embeddings_flax.py

@@ -84,10 +84,11 @@ class FlaxTimesteps(nn.Module):
                 Time step embedding dimension
     """
     dim: int = 32
+    flip_sin_to_cos: bool = False
     freq_shift: float = 1
 
     @nn.compact
     def __call__(self, timesteps):
         return get_sinusoidal_embeddings(
-            timesteps, embedding_dim=self.dim, freq_shift=self.freq_shift, flip_sin_to_cos=True
+            timesteps, embedding_dim=self.dim, flip_sin_to_cos=self.flip_sin_to_cos, freq_shift=self.freq_shift
         )

src/diffusers/models/unet_2d_condition_flax.py

@@ -85,6 +85,10 @@ class FlaxUNet2DConditionModel(nn.Module, FlaxModelMixin, ConfigMixin):
             The dimension of the cross attention features.
         dropout (`float`, *optional*, defaults to 0):
             Dropout probability for down, up and bottleneck blocks.
+        flip_sin_to_cos (`bool`, *optional*, defaults to `True`):
+            Whether to flip the sin to cos in the time embedding.
+        freq_shift (`int`, *optional*, defaults to 0): The frequency shift to apply to the time embedding.
+
     """
 
     sample_size: int = 32
@@ -105,6 +109,7 @@ class FlaxUNet2DConditionModel(nn.Module, FlaxModelMixin, ConfigMixin):
     dropout: float = 0.0
     use_linear_projection: bool = False
     dtype: jnp.dtype = jnp.float32
+    flip_sin_to_cos: bool = True
     freq_shift: int = 0
 
     def init_weights(self, rng: jax.random.PRNGKey) -> FrozenDict:
@@ -133,7 +138,9 @@ class FlaxUNet2DConditionModel(nn.Module, FlaxModelMixin, ConfigMixin):
         )
 
         # time
-        self.time_proj = FlaxTimesteps(block_out_channels[0], freq_shift=self.config.freq_shift)
+        self.time_proj = FlaxTimesteps(
+            block_out_channels[0], flip_sin_to_cos=self.flip_sin_to_cos, freq_shift=self.config.freq_shift
+        )
         self.time_embedding = FlaxTimestepEmbedding(time_embed_dim, dtype=self.dtype)
 
         only_cross_attention = self.only_cross_attention