From 6050ab7add7f362e6c3e820156513a6e9e8c0708 Mon Sep 17 00:00:00 2001
From: Andrew Leech <andrew.leech@planetinnovation.com.au>
Date: Fri, 19 Aug 2022 13:52:37 +1000
Subject: [PATCH 1/2] py/Makefile: Add helper to declare variables as
 dependencies.

depend_var is a function that can be used to add a virtual dependency
to a target based on the given make variable, eg:
$(OBJ): $(call depend_var, MY_VAR)
---
 py/mkenv.mk   | 5 +++++
 py/mkrules.mk | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/py/mkenv.mk b/py/mkenv.mk
index ea2e34f3b6..b1deaa50b2 100644
--- a/py/mkenv.mk
+++ b/py/mkenv.mk
@@ -29,6 +29,11 @@ else
 Q =
 endif
 
+# depend_var is a function that can be used to add a virtual dependency
+# to a target based on the given make variable.
+# eg. $(OBJ): $(call depend_var, MY_VAR)
+depend_var = $(BUILD)/dependvar/$(strip $(1))+$(shell echo $($(strip $(1))) | md5sum | cut -d ' ' -f 1)
+
 # default settings; can be overridden in main Makefile
 
 PY_SRC ?= $(TOP)/py
diff --git a/py/mkrules.mk b/py/mkrules.mk
index 14f1b953cd..af7e2bff52 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -25,6 +25,14 @@ QSTR_GEN_CFLAGS += $(QSTR_GEN_FLAGS)
 QSTR_GEN_CXXFLAGS := $(CXXFLAGS)
 QSTR_GEN_CXXFLAGS += $(QSTR_GEN_FLAGS)
 
+# depend_var is a function that can be used to add a virtual dependency
+# to a target based on the given make variable.
+# eg. $(OBJ): $(call depend_var, MY_VAR)
+$(BUILD)/dependvar/%:
+	@mkdir -p $(BUILD)/dependvar
+	@rm -f $(BUILD)/dependvar/$(firstword $(subst +, ,$*))+*
+	$(Q)echo $($(firstword $(subst +, ,$*))) > $@
+
 # This file expects that OBJ contains a list of all of the object files.
 # The directory portion of each object file is used to locate the source
 # and should not contain any ..'s but rather be relative to the top of the

From fb7ba43d8181189a92708f6354e71744a716f5b3 Mon Sep 17 00:00:00 2001
From: Andrew Leech <andrew.leech@planetinnovation.com.au>
Date: Fri, 19 Aug 2022 13:53:22 +1000
Subject: [PATCH 2/2] stm32/Makefile: Automatically rebuild if make
 USE_MBOOT=0/1 changed.

---
 ports/stm32/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index ee00d77173..b24108327e 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -714,6 +714,9 @@ SRC_QSTR_AUTO_DEPS += $(GEN_CDCINF_HEADER)
 # which source files might need it.
 $(OBJ): | $(GEN_PINS_HDR)
 
+# Automatically rebuild if specific settings are changed on command line
+$(OBJ): $(call depend_var, USE_MBOOT)
+
 # With conditional pins, we may need to regenerate qstrdefs.h when config
 # options change.
 $(HEADER_BUILD)/qstrdefs.generated.h: $(BOARD_DIR)/mpconfigboard.h