diff --git a/src/librustc_target/abi/call/avr.rs b/src/librustc_target/abi/call/avr.rs
index f681302bc03..c1f7a1e3af5 100644
--- a/src/librustc_target/abi/call/avr.rs
+++ b/src/librustc_target/abi/call/avr.rs
@@ -1,20 +1,46 @@
-#![allow(non_upper_case_globals)]
+//! LLVM-frontend specific AVR calling convention implementation.
+//!
+//! # Current calling convention ABI
+//!
+//! Inherited from Clang's `clang::DefaultABIInfo` implementation - self described
+//! as
+//!
+//! > the default implementation for ABI specific details. This implementation
+//! > provides information which results in
+//! > self-consistent and sensible LLVM IR generation, but does not
+//! > conform to any particular ABI.
+//! >
+//! > - Doxygen Doxumentation of `clang::DefaultABIInfo`
+//!
+//! This calling convention may not match AVR-GCC in all cases.
+//!
+//! In the future, an AVR-GCC compatible argument classification ABI should be
+//! adopted in both Rust and Clang.
+//!
+//! *NOTE*: Currently, this module implements the same calling convention
+//! that clang with AVR currently does - the default, simple, unspecialized
+//! ABI implementation available to all targets. This ABI is not
+//! binary-compatible with AVR-GCC. Once LLVM [PR46140](https://bugs.llvm.org/show_bug.cgi?id=46140)
+//! is completed, this module should be updated to match so that both Clang
+//! and Rust emit code to the same AVR-GCC compatible ABI.
+//!
+//! In particular, both Clang and Rust may not have the same semantics
+//! when promoting arguments to indirect references as AVR-GCC. It is important
+//! to note that the core AVR ABI implementation within LLVM itself is ABI
+//! compatible with AVR-GCC - Rust and AVR-GCC only differ in the small amount
+//! of compiler frontend specific calling convention logic implemented here.
 
 use crate::abi::call::{ArgAbi, FnAbi};
 
 fn classify_ret_ty<Ty>(ret: &mut ArgAbi<'_, Ty>) {
     if ret.layout.is_aggregate() {
         ret.make_indirect();
-    } else {
-        ret.extend_integer_width_to(8); // Is 8 correct?
     }
 }
 
 fn classify_arg_ty<Ty>(arg: &mut ArgAbi<'_, Ty>) {
     if arg.layout.is_aggregate() {
         arg.make_indirect();
-    } else {
-        arg.extend_integer_width_to(8);
     }
 }