rust: Enable incremental compilation

Signed-off-by: Asahi Lina <lina@asahilina.net>

Makefile

@@ -120,6 +120,13 @@ endif
 
 export KBUILD_CHECKSRC
 
+# Enable Rust incremental compilation.
+#
+# Use 'make RUST_INCREMENTAL=1' to enable it.
+ifeq ("$(origin RUST_INCREMENTAL)", "command line")
+  KBUILD_RUST_INCREMENTAL := $(RUST_INCREMENTAL)
+endif
+
 # Enable "clippy" (a linter) as part of the Rust compilation.
 #
 # Use 'make CLIPPY=1' to enable it.

drivers/gpu/drm/asahi/Makefile

@@ -1,3 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_DRM_ASAHI) += asahi.o
+obj-$(CONFIG_DRM_ASAHI) += asahi.a

scripts/Makefile.build

@@ -279,6 +279,7 @@ rust_allowed_features := allocator_api,array_from_fn,bench_black_box,core_ffi_c,
 
 rust_common_cmd = \
 	RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
+	$(if $(RUST_INCREMENTAL),-Cincremental=$(obj)/rust_incremental,) \
 	-Zallow-features=$(rust_allowed_features) \
 	-Zcrate-attr=no_std \
 	-Zcrate-attr='feature($(rust_allowed_features))' \
@@ -306,6 +307,15 @@ quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
 $(obj)/%.o: $(src)/%.rs FORCE
 	$(call if_changed_dep,rustc_o_rs)
 
+quiet_cmd_rustc_a_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
+      cmd_rustc_a_rs = \
+	$(rust_common_cmd) --emit=dep-info,link -Ccodegen-units=32 $<; \
+	mv $(dir $@)/$(patsubst %.a,lib%.rlib,$(notdir $@)) $@; \
+	$(rust_handle_depfile)
+
+$(obj)/%.a: $(src)/%.rs FORCE
+	$(call if_changed_dep,rustc_a_rs)
+
 quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_rsi_rs = \
 	$(rust_common_cmd) --emit=dep-info -Zunpretty=expanded $< >$@; \

scripts/mod/modpost.c

@@ -774,6 +774,7 @@ static const char *const section_white_list[] =
 	".fmt_slot*",			/* EZchip */
 	".gnu.lto*",
 	".discard.*",
+	".rmeta",
 	NULL
 };