[PATCH v2 20/33] rust: kbuild: update `bindgen --rust-target` version and replace comment

[Miguel Ojeda <ojeda@kernel.org>]

As the comment in the `Makefile` explains, previously, we needed to
limit ourselves to the list of Rust versions known by `bindgen` for its
`--rust-target` option [1].

In other words, we needed to consult the versions known by the minimum
version of `bindgen` that we supported.

Now that we bumped the minimum version of `bindgen`, that limitation
does not apply anymore since `bindgen` 0.71.0 [2].

Thus replace the comment and simply write our minimum supported Rust
version there, which is much simpler.

See commit 7a5f93ea5862 ("rust: kbuild: set `bindgen`'s Rust target
version") for more details.

Link: https://rust-lang.zulipchat.com/#narrow/channel/425075-rust-for-linux/topic/rust.20version.20on.20generated.20bindings/near/484087179 [1]
Link: https://github.com/rust-lang/rust-bindgen/pull/2993 [2]
Reviewed-by: Tamir Duberstein <tamird@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/Makefile | 16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

diff --git a/rust/Makefile b/rust/Makefile
index 54498cb5b851..866f9afc1b7f 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -441,22 +441,10 @@ endif
 # architecture instead of generating `usize`.
 bindgen_c_flags_final = $(bindgen_c_flags_lto) -fno-builtin -D__BINDGEN__
 
-# Each `bindgen` release may upgrade the list of Rust target versions. By
-# default, the highest stable release in their list is used. Thus we need to set
-# a `--rust-target` to avoid future `bindgen` releases emitting code that
-# `rustc` may not understand. On top of that, `bindgen` does not support passing
-# an unknown Rust target version.
-#
-# Therefore, the Rust target for `bindgen` can be only as high as the minimum
-# Rust version the kernel supports and only as high as the greatest stable Rust
-# target supported by the minimum `bindgen` version the kernel supports (that
-# is, if we do not test the actual `rustc`/`bindgen` versions running).
-#
-# Starting with `bindgen` 0.71.0, we will be able to set any future Rust version
-# instead, i.e. we will be able to set here our minimum supported Rust version.
+# `--rust-target` points to our minimum supported Rust version.
 quiet_cmd_bindgen = BINDGEN $@
       cmd_bindgen = \
-	$(BINDGEN) $< $(bindgen_target_flags) --rust-target 1.68 \
+	$(BINDGEN) $< $(bindgen_target_flags) --rust-target 1.85 \
 		--use-core --with-derive-default --ctypes-prefix ffi --no-layout-tests \
 		--no-debug '.*' --enable-function-attribute-detection \
 		-o $@ -- $(bindgen_c_flags_final) -DMODULE \
-- 
2.53.0