[PATCH] scripts/Makefile.dts: tweak logic for deciding which dtbs to build

[Rasmus Villemoes]

The idea in 3609e1dc5f4d (dts: automatically build necessary .dtb
files) was fine, but the implementation was suboptimal due to some
misunderstandings on my part (and possibly defects in some defconfig
files):

- Sometimes DEFAULT_DEVICE_TREE is not included in OF_LIST or
  SPL_OF_LIST

- SPL_OF_LIST is not always a subset of OF_LIST

- While SPL_OF_LIST governs the list of dtbs relevant to SPL (i.e.,
  may be built into an
  SPL-with-bunch-of-dtbs-to-choose-between-at-runtime), those dtbs are
  not actually _built_ during the SPL build phase, i.e. when $(SPL_)
  would expand to SPL_. fdtgrep runs on the artifacts produced during
  the ordinary U-Boot build.

Tweak the logic so that we simply add the union of all dtbs mentioned
in either DEFAULT_DEVICE_TREE, OF_LIST and SPL_OF_LIST to dtb-y. That
should, for real, ensure that we always build all the dtbs that is
relevant to the current board, and should in turn enable us to
massively simplify arch/*/dts/Makefile.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
---
Per https://lore.kernel.org/u-boot/20230503145438.GB1134230@bill-the-cat/

I guess one could apply make's built-in sort function since the RHS is
very likely to contain some duplicates, but I don't think it really
matters. So for now I'm just posting the version of the patch that Tom
tested.

 scripts/Makefile.dts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/Makefile.dts b/scripts/Makefile.dts
index 2561025da8..5e2429c617 100644
--- a/scripts/Makefile.dts
+++ b/scripts/Makefile.dts
@@ -1,3 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0+
 
-dtb-y += $(patsubst %,%.dtb,$(subst ",,$(CONFIG_$(SPL_)OF_LIST)))
+dtb-y += $(patsubst %,%.dtb,$(subst ",,$(CONFIG_DEFAULT_DEVICE_TREE) $(CONFIG_OF_LIST) $(CONFIG_SPL_OF_LIST)))
-- 
2.37.2