[WIP]Flax training script for controlnet (#2818)

* add train_controlnet_flax

---------
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

examples/controlnet/README.md

@@ -267,3 +267,99 @@ image = pipe(
 
 image.save("./output.png")
 ```
+
+## Training with Flax/JAX
+
+For faster training on TPUs and GPUs you can leverage the flax training example. Follow the instructions above to get the model and dataset before running the script.
+
+### Running on Google Cloud TPU
+
+See below for commands to set up a TPU VM(`--accelerator-type v4-8`). For more details about how to set up and use TPUs, refer to [Cloud docs for single VM setup](https://cloud.google.com/tpu/docs/run-calculation-jax).
+
+First create a single TPUv4-8 VM and connect to it:
+
+```
+ZONE=us-central2-b
+TPU_TYPE=v4-8
+VM_NAME=hg_flax
+
+gcloud alpha compute tpus tpu-vm create $VM_NAME \
+    --zone $ZONE \
+    --accelerator-type $TPU_TYPE \
+    --version  tpu-vm-v4-base
+
+gcloud alpha compute tpus tpu-vm ssh $VM_NAME --zone $ZONE -- \
+```
+
+When connected install JAX `0.4.5`:
+
+```
+pip install "jax[tpu]==0.4.5" -f https://storage.googleapis.com/jax-releases/libtpu_releases.html
+```
+
+To verify that JAX was correctly installed, you can run the following command:
+
+```
+import jax
+jax.device_count()
+```
+
+This should display the number of TPU cores, which should be 4 on a TPUv4-8 VM.
+
+Then install Diffusers and the library's training dependencies:
+
+```bash
+git clone https://github.com/huggingface/diffusers
+cd diffusers
+pip install .
+```
+
+Then cd in the example folder and run
+
+```bash
+pip install -U -r requirements_flax.txt
+```
+
+Now let's downloading two conditioning images that we will use to run validation during the training in order to track our progress
+
+```
+wget https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/controlnet_training/conditioning_image_1.png
+wget https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/diffusers/controlnet_training/conditioning_image_2.png
+```
+
+We encourage you to store or share your model with the community. To use huggingface hub, please login to your Hugging Face account, or ([create one](https://huggingface.co/docs/diffusers/main/en/training/hf.co/join) if you don’t have one already):
+
+```
+huggingface-cli login
+```
+
+Make sure you have the `MODEL_DIR`,`OUTPUT_DIR` and `HUB_MODEL_ID` environment variables set. The `OUTPUT_DIR` and `HUB_MODEL_ID` variables specify where to save the model to on the Hub:
+
+```
+export MODEL_DIR="runwayml/stable-diffusion-v1-5"
+export OUTPUT_DIR="control_out"
+export HUB_MODEL_ID="fill-circle-controlnet"
+```
+
+And finally start the training
+
+```
+python3 train_controlnet_flax.py \
+ --pretrained_model_name_or_path=$MODEL_DIR \
+ --output_dir=$OUTPUT_DIR \
+ --dataset_name=fusing/fill50k \
+ --resolution=512 \
+ --learning_rate=1e-5 \
+ --validation_image "./conditioning_image_1.png" "./conditioning_image_2.png" \
+ --validation_prompt "red circle with blue background" "cyan circle with brown floral background" \
+ --validation_steps=1000 \
+ --train_batch_size=2 \
+ --revision="non-ema" \
+ --from_pt \
+ --report_to="wandb" \
+ --max_train_steps=10000 \
+ --push_to_hub \
+ --hub_model_id=$HUB_MODEL_ID
+ ```
+
+Since we passed the `--push_to_hub` flag, it will automatically create a model repo under your huggingface account based on `$HUB_MODEL_ID`. By the end of training, the final checkpoint will be automatically stored on the hub. You can find an example model repo [here](https://huggingface.co/YiYiXu/fill-circle-controlnet).