Refactor DiffusionModelUNetMaisi (#7989)

Fixes #7988 .

### Description

Refactor DiffusionModelUNetMaisi to use monai core components. 

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [ ] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [ ] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

---------

Signed-off-by: Pengfei Guo <pengfeig@nvidia.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

monai/apps/generation/maisi/networks/diffusion_model_unet_maisi.py

@@ -37,21 +37,15 @@
 from torch import nn
 
 from monai.networks.blocks import Convolution
-from monai.utils import ensure_tuple_rep, optional_import
-from monai.utils.type_conversion import convert_to_tensor
-
-get_down_block, has_get_down_block = optional_import(
-    "generative.networks.nets.diffusion_model_unet", name="get_down_block"
-)
-get_mid_block, has_get_mid_block = optional_import(
-    "generative.networks.nets.diffusion_model_unet", name="get_mid_block"
-)
-get_timestep_embedding, has_get_timestep_embedding = optional_import(
-    "generative.networks.nets.diffusion_model_unet", name="get_timestep_embedding"
+from monai.networks.nets.diffusion_model_unet import (
+    get_down_block,
+    get_mid_block,
+    get_timestep_embedding,
+    get_up_block,
+    zero_module,
 )
-get_up_block, has_get_up_block = optional_import("generative.networks.nets.diffusion_model_unet", name="get_up_block")
-xformers, has_xformers = optional_import("xformers")
-zero_module, has_zero_module = optional_import("generative.networks.nets.diffusion_model_unet", name="zero_module")
+from monai.utils import ensure_tuple_rep
+from monai.utils.type_conversion import convert_to_tensor
 
 __all__ = ["DiffusionModelUNetMaisi"]
 
@@ -78,6 +72,8 @@ class DiffusionModelUNetMaisi(nn.Module):
         cross_attention_dim: Number of context dimensions to use.
         num_class_embeds: If specified (as an int), then this model will be class-conditional with `num_class_embeds` classes.
         upcast_attention: If True, upcast attention operations to full precision.
+        include_fc: whether to include the final linear layer. Default to False.
+        use_combined_linear: whether to use a single linear layer for qkv projection, default to False.
         use_flash_attention: If True, use flash attention for a memory efficient attention mechanism.
         dropout_cattn: If different from zero, this will be the dropout value for the cross-attention layers.
         include_top_region_index_input: If True, use top region index input.
@@ -102,6 +98,8 @@ def __init__(
         cross_attention_dim: int | None = None,
         num_class_embeds: int | None = None,
         upcast_attention: bool = False,
+        include_fc: bool = False,
+        use_combined_linear: bool = False,
         use_flash_attention: bool = False,
         dropout_cattn: float = 0.0,
         include_top_region_index_input: bool = False,
@@ -152,9 +150,6 @@ def __init__(
                 "`num_channels`."
             )
 
-        if use_flash_attention and not has_xformers:
-            raise ValueError("use_flash_attention is True but xformers is not installed.")
-
         if use_flash_attention is True and not torch.cuda.is_available():
             raise ValueError(
                 "torch.cuda.is_available() should be True but is False. Flash attention is only available for GPU."
@@ -210,7 +205,6 @@ def __init__(
             input_channel = output_channel
             output_channel = num_channels[i]
             is_final_block = i == len(num_channels) - 1
-
             down_block = get_down_block(
                 spatial_dims=spatial_dims,
                 in_channels=input_channel,
@@ -227,6 +221,8 @@ def __init__(
                 transformer_num_layers=transformer_num_layers,
                 cross_attention_dim=cross_attention_dim,
                 upcast_attention=upcast_attention,
+                include_fc=include_fc,
+                use_combined_linear=use_combined_linear,
                 use_flash_attention=use_flash_attention,
                 dropout_cattn=dropout_cattn,
             )
@@ -245,6 +241,8 @@ def __init__(
             transformer_num_layers=transformer_num_layers,
             cross_attention_dim=cross_attention_dim,
             upcast_attention=upcast_attention,
+            include_fc=include_fc,
+            use_combined_linear=use_combined_linear,
             use_flash_attention=use_flash_attention,
             dropout_cattn=dropout_cattn,
         )
@@ -280,6 +278,8 @@ def __init__(
                 transformer_num_layers=transformer_num_layers,
                 cross_attention_dim=cross_attention_dim,
                 upcast_attention=upcast_attention,
+                include_fc=include_fc,
+                use_combined_linear=use_combined_linear,
                 use_flash_attention=use_flash_attention,
                 dropout_cattn=dropout_cattn,
             )

tests/test_diffusion_model_unet_maisi.py

@@ -17,14 +17,11 @@
 import torch
 from parameterized import parameterized
 
+from monai.apps.generation.maisi.networks.diffusion_model_unet_maisi import DiffusionModelUNetMaisi
 from monai.networks import eval_mode
 from monai.utils import optional_import
 
 _, has_einops = optional_import("einops")
-_, has_generative = optional_import("generative")
-
-if has_generative:
-    from monai.apps.generation.maisi.networks.diffusion_model_unet_maisi import DiffusionModelUNetMaisi
 
 UNCOND_CASES_2D = [
     [
@@ -291,7 +288,6 @@
 ]
 
 
-@skipUnless(has_generative, "monai-generative required")
 class TestDiffusionModelUNetMaisi2D(unittest.TestCase):
 
     @parameterized.expand(UNCOND_CASES_2D)
@@ -510,7 +506,6 @@ def test_shape_with_additional_inputs(self, input_param):
             self.assertEqual(result.shape, (1, 1, 16, 16))
 
 
-@skipUnless(has_generative, "monai-generative required")
 class TestDiffusionModelUNetMaisi3D(unittest.TestCase):
 
     @parameterized.expand(UNCOND_CASES_3D)