MIPS: qemu-malta: generate swapped image as part of multi-image build

Having to manually swap the words in the MIPS Malta image for QEMU
little endian emulation is annoying.

Have the multi-image build for Malta generate a second .swapped
image that can be readily used if needed.

Signed-off-by: Ahmad Fatoum <[email protected]>
Link: https://lore.barebox.org/[email protected]
Signed-off-by: Sascha Hauer <[email protected]>

Documentation/boards/mips/qemu-malta.rst

@@ -10,31 +10,23 @@ QEMU run string:
 
   qemu-system-mips -nodefaults -M malta -m 256 \
       -device VGA -serial stdio -monitor null \
-      -bios barebox-flash-image
+      -bios ./images/barebox-qemu-malta.img
 
 
 Little-endian mode
 ------------------
 
-Running little-endian Malta is a bit tricky.
 In little-endian mode the 32bit words in the boot flash image are swapped,
 a neat trick which allows bi-endian firmware.
 
-You have to swap words of ``zbarebox.bin`` image, e.g.:
-
-.. code-block:: sh
-
-  echo arch/mips/pbl/zbarebox.bin \
-      | cpio --create \
-      | cpio --extract --swap --unconditional
-
-QEMU run string:
+The barebox build generates a second ``./images/barebox-qemu-malta.img.swapped``
+image that can be used in this case, e.g.:
 
 .. code-block:: sh
 
   qemu-system-mipsel -nodefaults -M malta -m 256 \
       -device VGA -serial stdio -monitor null \
-      -bios barebox-flash-image
+      -bios ./images/barebox-qemu-malta.img.swapped
 
 
 Using GXemul

images/.gitignore

@@ -32,3 +32,4 @@ barebox.sum
 *.mvebu1img
 *.stm32
 *.nmon
+*.swapped

images/Makefile

@@ -218,5 +218,5 @@ $(flash-list): $(image-y-path)
 clean-files := *.pbl *.pblb *.map start_*.imximg *.img barebox.z start_*.kwbimg \
 	start_*.kwbuartimg *.socfpgaimg *.mlo *.t20img *.t20img.cfg *.t30img \
 	*.t30img.cfg *.t124img *.t124img.cfg *.mlospi *.mlo *.mxsbs *.mxssd \
-	start_*.simximg start_*.usimximg *.zynqimg *.image
+	start_*.simximg start_*.usimximg *.zynqimg *.image *.swapped
 clean-files += pbl.lds

images/Makefile.malta

@@ -1,3 +1,11 @@
+quiet_cmd_bswap32_image = BSWAP4  $@
+      cmd_bswap32_image = cp $< $@ && \
+			  truncate -s %4 $@ && \
+			  objcopy -I binary --reverse-byte=4 $@
+
+$(obj)/%.img.swapped: $(obj)/%.img FORCE
+	$(call if_changed,bswap32_image)
+
 pblb-$(CONFIG_BOARD_QEMU_MALTA) += start_qemu_malta
 FILE_barebox-qemu-malta.img = start_qemu_malta.pblb
-image-$(CONFIG_BOARD_QEMU_MALTA) += barebox-qemu-malta.img
+image-$(CONFIG_BOARD_QEMU_MALTA) += barebox-qemu-malta.img barebox-qemu-malta.img.swapped