[PATCH v2] firmware: fix missing firmware handling for external firmware

[Sascha Hauer <s.hauer@pengutronix.de>]

From: Marco Felsch <m.felsch@pengutronix.de>

Currently we depend on the external firmware file since we need it for
the sha256sum. But this dependency break the 'optional missing firmware'
feature.

Fix this by dropping the firmware file prerequisite and instead evaluate
the FWNAME_EXISTS variable. If the firmware file does not exist a dummy
file is created and the build continues till the linking process (like
we do for the other firmware).

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Link: https://lore.barebox.org/20240110145908.3965855-1-m.felsch@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 firmware/Makefile    | 4 ++--
 images/Makefile      | 2 +-
 scripts/Makefile.lib | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/firmware/Makefile b/firmware/Makefile
index 2323b46f96..5bc6649a45 100644
--- a/firmware/Makefile
+++ b/firmware/Makefile
@@ -92,8 +92,8 @@ $(obj)/%.extgen.S: $(obj)/%.sha.bin FORCE
 $(obj)/%.sha.bin: $(obj)/%.sum FORCE
 	$(call if_changed,sha256bin)
 
-$(obj)/%.sum: $(obj)/% FORCE
-	$(call if_changed,sha256sum)
+$(obj)/%.sum: FORCE
+	$(if $(wildcard $(fwdir)/$*), $(call if_changed,sha256sum,$(fwdir)/$*), @touch $@)
 
 clean-files += *.sha.bin *.sum
 
diff --git a/images/Makefile b/images/Makefile
index 7b4e019531..c0105609ee 100644
--- a/images/Makefile
+++ b/images/Makefile
@@ -132,7 +132,7 @@ $(obj)/barebox.sha.bin: $(obj)/barebox.sum FORCE
 	$(call if_changed,sha256bin)
 
 $(obj)/barebox.sum: $(obj)/barebox.z FORCE
-	$(call if_changed,sha256sum)
+	$(call if_changed,sha256sum,$<)
 
 
 # barebox.z - compressed barebox binary
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0b236babb2..f205e08afc 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -301,7 +301,7 @@ quiet_cmd_sha256bin ?= SHA-BIN $@
 			while read -r byte; do printf '\%o' $$byte; done)" > $@
 
 quiet_cmd_sha256sum ?= SHA     $@
-      cmd_sha256sum ?= sha256sum $< > $@
+      cmd_sha256sum ?= sha256sum $2 > $@
 
 # Decompressor for barebox proper binary when using PBL
 # ---------------------------------------------------------------------------
-- 
2.39.2