Group use vs mod statements

Consider the following:

use std::borrow::Cow;
use std::alloc::GlobalAlloc;
pub mod baz;
use std::cell::Cell;
use std::ascii::AsciiExt;

When running rustfmt, this sorts the use statements alphabetically, but leaves the mod in place:

use std::alloc::GlobalAlloc;
use std::borrow::Cow;
pub mod baz;
use std::ascii::AsciiExt;
use std::cell::Cell;

1. Is there an established convention for whether all mod statements should go above or below all use?
2. If so, is there a way to enforce that in rustfmt?

Start by running rustfmt on the Rust snippet in the issue and comparing how it orders the use and mod statements. Determine whether the project has an established ordering convention, then check whether rustfmt exposes a relevant configuration or entry point. Done means the convention is documented or the requested ordering can be consistently enforced.