You must convert layer or layers with photo to Smart Object layer before using Camera Raw filter. Save as PSD and double click on filter name (Camera Raw Filter in this case) if you want to edit it at any time.
I get the impression you're not clear on the difference between the camera raw plugin, used for raw files, and the camera raw filter, used on RGB files in Photoshop. They are not the same thing.
The ACR filter "borrows" the ACR engine and interface, but other than that it acts like any other filter. Once committed, you can't edit it. The way to make it re-editable is as Bojan says, and this applies to all filters: turn it into a smart object first.