From 39e3ab3e857a617b982dbeee2037f13edc46f799 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Mon, 23 Sep 2019 09:26:41 +0100
Subject: [PATCH] kbuild: Allow .dtbo overlays to be built piecemeal

Before 4.20, it was possible to build an arbitrary overlay by copying
it to arm/boot/dts/overlays/mytest-overlay.dts and running:

    make ARCH=arm overlays/mytest.dtbo

In 4.20 the .dtb build rules were centralised, requiring the dowstream
.dtbo build rules to be changed. They were, enough to support "make ...
dtbs", but not sufficiently to allow this ad-hoc, one-off building of
individual files.

Add the missing makefile rule to support this way of building.

See: https://github.com/raspberrypi/linux/issues/3250

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)

--- a/Makefile
+++ b/Makefile
@@ -1376,6 +1376,9 @@ ifneq ($(dtstree),)
 %.dtb: include/config/kernel.release scripts_dtc
 	$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
 
+%.dtbo: prepare3 scripts_dtc
+	$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+
 PHONY += dtbs dtbs_install dtbs_check
 dtbs: include/config/kernel.release scripts_dtc
 	$(Q)$(MAKE) $(build)=$(dtstree)
