build: Revive and update LDR format support

LDR format files are used primarily by Analog Devices processors but may
be of interest to other vendors. Previously support existed for this
format as part of the U-Boot build, but it has been unmaintained and
unused for a long time. In preparation for adding support for modern ADI
processors that use LDR, modernize the LDR support:

- Introduce CONFIG_LDR_CPU as the CPU string recognized by the LDR tool
  may not be the same as CONFIG_CPU
- Add an SPL target that repackages u-boot-spl inside an LDR file

An almost identical target for packaging u-boot into an LDR file already
exists and did not need to be created.

Co-developed-by: Nathan Barrett-Morrison <[email protected]>
Signed-off-by: Nathan Barrett-Morrison <[email protected]>
Signed-off-by: Ian Roberts <[email protected]>
Signed-off-by: Greg Malysa <[email protected]>

Kconfig

@@ -715,6 +715,20 @@ config SYS_CLK_FREQ
 	  A static value for the CPU frequency.  Note that if not required
 	  for a given SoC, this can be left at 0.
 
+config HAS_LDR
+	bool
+	help
+	  Enables building .ldr targets for U-Boot and SPL. This does not
+	  automatically build any additional targets with make or buildman.
+
+config LDR_CPU
+	string "CPU name to be passed to LDR utility."
+	depends on HAS_LDR
+	help
+	  Set the CPU name for the -T parameter in the LDR utility.  This is
+	  generally used on processors from Analog Devices, but may be also
+	  be useful for other vendors.
+
 source "api/Kconfig"
 
 endmenu		# General setup

Makefile

@@ -1360,7 +1360,7 @@ u-boot-nodtb.bin: u-boot FORCE
 
 u-boot.ldr:	u-boot
 		$(CREATE_LDR_ENV)
-		$(LDR) -T $(CONFIG_CPU) -c $@ $< $(LDR_FLAGS)
+		$(LDR) -T $(CONFIG_LDR_CPU) -c $@ $< $(LDR_FLAGS)
 		$(BOARD_SIZE_CHECK)
 
 # binman

scripts/Makefile.spl

@@ -381,6 +381,11 @@ $(obj)/$(BOARD)-spl.bin: $(obj)/u-boot-spl.bin
 	$(objtree)/tools/mkexynosspl) $(VAR_SIZE_PARAM) $< $@
 endif
 
+$(obj)/u-boot-spl.ldr: $(obj)/u-boot-spl
+	$(CREATE_LDR_ENV)
+	$(LDR) -T $(CONFIG_LDR_CPU) -c $@ $< $(LDR_FLAGS)
+	$(BOARD_SIZE_CHECK)
+
 quiet_cmd_objcopy = OBJCOPY $@
 cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@