Allow boards to initialize the DT at runtime.

In some boards like the Raspberry Pi the initial bootloader will pass
a DT to the kernel. When using U-Boot as such kernel, the board code in
U-Boot should be able to provide U-Boot with this, already assembled
device tree blob.

This patch introduces a new config option CONFIG_OF_BOARD to use instead
of CONFIG_OF_EMBED or CONFIG_OF_SEPARATE which will initialize the DT
from a board-specific funtion instead of bundling one with U-Boot or as
a separated file. This allows boards like the Raspberry Pi to reuse the
device tree passed from the bootcode.bin and start.elf firmware
files, including the run-time selected device tree overlays.

Signed-off-by: Alex Deymo <deymo@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

README

@@ -968,7 +968,7 @@ The following options need to be configured:
 		tree is available in the global data as gd->fdt_blob.
 
 		U-Boot needs to get its device tree from somewhere. This can
-		be done using one of the two options below:
+		be done using one of the three options below:
 
 		CONFIG_OF_EMBED
 		If this variable is defined, U-Boot will embed a device tree
@@ -989,6 +989,12 @@ The following options need to be configured:
 		still use the individual files if you need something more
 		exotic.
 
+		CONFIG_OF_BOARD
+		If this variable is defined, U-Boot will use the device tree
+		provided by the board at runtime instead of embedding one with
+		the image. Only boards defining board_fdt_blob_setup() support
+		this option (see include/fdtdec.h file).
+
 - Watchdog:
 		CONFIG_WATCHDOG
 		If this variable is defined, it enables watchdog

board/raspberrypi/rpi/rpi.c

@@ -470,6 +470,16 @@ int board_init(void)
 	return bcm2835_power_on_module(BCM2835_MBOX_POWER_DEVID_USB_HCD);
 }
 
+/*
+ * If the firmware passed a device tree use it for U-Boot.
+ */
+void *board_fdt_blob_setup(void)
+{
+	if (fdt_magic(fw_dtb_pointer) != FDT_MAGIC)
+		return NULL;
+	return (void *)fw_dtb_pointer;
+}
+
 int ft_board_setup(void *blob, bd_t *bd)
 {
 	/*

doc/README.fdt-control

@@ -130,6 +130,10 @@ u-boot-dtb.bin which does the above step for you also. If you are using
 CONFIG_SPL_FRAMEWORK, then u-boot.img will be built to include the device
 tree binary.
 
+If CONFIG_OF_BOARD is defined, a board-specific routine will provide the
+device tree at runtime, for example if an earlier bootloader stage creates
+it and passes it to U-Boot.
+
 If CONFIG_OF_HOSTFILE is defined, then it will be read from a file on
 startup. This is only useful for sandbox. Use the -d flag to U-Boot to
 specify the file to read.

dts/Kconfig

@@ -51,6 +51,14 @@ config OF_EMBED
 	  and development only and is not recommended for production devices.
 	  Boards in the mainline U-Boot tree should not use it.
 
+config OF_BOARD
+	bool "Provided by the board at runtime"
+	depends on !SANDBOX
+	help
+	  If this option is enabled, the device tree will be provided by
+	  the board at runtime if the board supports it, instead of being
+	  bundled with the image.
+
 config OF_HOSTFILE
 	bool "Host filed DTB for DT control"
 	depends on SANDBOX

include/fdtdec.h

@@ -1023,4 +1023,10 @@ int fdtdec_setup_memory_banksize(void);
  */
 int fdtdec_setup(void);
 
+/**
+ * Board-specific FDT initialization. Returns the address to a device tree blob.
+ * Called when CONFIG_OF_BOARD is defined.
+ */
+void *board_fdt_blob_setup(void);
+
 #endif

lib/fdtdec.c

@@ -1255,6 +1255,9 @@ int fdtdec_setup(void)
 	/* FDT is at end of image */
 	gd->fdt_blob = (ulong *)&_end;
 #  endif
+# elif defined(CONFIG_OF_BOARD)
+	/* Allow the board to override the fdt address. */
+	gd->fdt_blob = board_fdt_blob_setup();
 # elif defined(CONFIG_OF_HOSTFILE)
 	if (sandbox_read_fdt_from_file()) {
 		puts("Failed to read control FDT\n");