raspberrypi3: fix serial console (load pi3-miniuart-bt overlay)

- enable BR2_PACKAGE_RPI_FIRMWARE_INSTALL_DTB_OVERLAYS in raspberrypi3_defconfig
- add copy of rpi-firmware/overlays directory to boot partition in genimage-raspberrypi3.cfg
- enhance post-image.sh script to add 'dtoverlay=pi3-miniuart-bt' on request
- add BR2_ROOTFS_POST_SCRIPT_ARGS="--add-pi3-miniuart-bt-overlay" in raspberrypi3_defconfig

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/raspberrypi/genimage-raspberrypi3.cfg

@@ -7,6 +7,7 @@ image boot.vfat {
       "rpi-firmware/config.txt",
       "rpi-firmware/fixup.dat",
       "rpi-firmware/start.elf",
+      "rpi-firmware/overlays",
       "kernel-marked/zImage"
     }
   }

board/raspberrypi/post-image.sh

@@ -5,6 +5,19 @@ BOARD_NAME="$(basename ${BOARD_DIR})"
 GENIMAGE_CFG="${BOARD_DIR}/genimage-${BOARD_NAME}.cfg"
 GENIMAGE_TMP="${BUILD_DIR}/genimage.tmp"
 
+case "${2}" in
+	--add-pi3-miniuart-bt-overlay)
+	if ! grep -qE '^dtoverlay=' "${BINARIES_DIR}/rpi-firmware/config.txt"; then
+		echo "Adding 'dtoverlay=pi3-miniuart-bt' to config.txt (fixes ttyAMA0 serial console)."
+		cat << __EOF__ >> "${BINARIES_DIR}/rpi-firmware/config.txt"
+
+# fixes rpi3 ttyAMA0 serial console
+dtoverlay=pi3-miniuart-bt
+__EOF__
+	fi
+	;;
+esac
+
 # Mark the kernel as DT-enabled
 mkdir -p "${BINARIES_DIR}/kernel-marked"
 ${HOST_DIR}/usr/bin/mkknlimg "${BINARIES_DIR}/zImage" \

board/raspberrypi/readme.txt

@@ -60,7 +60,8 @@ After building, you should obtain this tree:
     |   +-- cmdline.txt
     |   +-- config.txt
     |   +-- fixup.dat
-    |   `-- start.elf
+    |   +-- start.elf
+    |   `-- overlays/               [3]
     +-- sdcard.img
     `-- zImage
 
@@ -69,6 +70,11 @@ After building, you should obtain this tree:
 
 [2] This is the mkknlimg DT-marked kernel.
 
+[3] Only for the Raspberry Pi 3 Model (overlay pi3-miniuart-bt is needed
+    to enable the RPi3 serial console otherwise occupied by the bluetooth
+    chip). Alternative would be to disable the serial console in cmdline.txt
+    and /etc/inittab.
+
 How to write the SD card
 ========================