rpi: Use the U-Boot control FDT for fdt_addr

The fdt_addr variable is used in extlinux as a fallback devicetree if
none is provided by the boot command.

The existing mechanism uses the devicetree provided to U-Boot, but in
its original, unrelocated position. For the rpi_4 I am using, this is
at 2b35ef00 which is not a convenient place in memory, if the ramdisk
is large.

U-Boot already deals with this sort of problem by relocating the FDT
to a safe address.

So use the control-FDT address instead.

Remove the existing comment, which is confusing, since the FDT is not
actually passed unmodified to the kernel: U-Boot adds various things
using its FDT-fixup mechanism.

Note that board_get_usable_ram_top() reduces the RAM top for boards with
less RAM. This behaviour is left unchanged as there is no other
mechanism for U-Boot to handle this.

Series-to: u-boot
Cover-letter:
rpi: Tidy up booting
This series allows rpi to boot a compressed Ubuntu kernel with ~100MB
ramdisk, by expanding the available space.

It also tidies up some strange behaviour with the provided FDT, where a
separate pointer is maintained to it, even though U-Boot has copied it
and placed it in its own space. This avoids strange bugs where it
accidentally gets overwritten when loading a file into memory.
END

Signed-off-by: Simon Glass <sjg@chromium.org>

board/raspberrypi/rpi/rpi.c

@@ -3,6 +3,8 @@
  * (C) Copyright 2012-2016 Stephen Warren
  */
 
+#define LOG_CATEGORY	LOGC_BOARD
+
 #include <config.h>
 #include <dm.h>
 #include <env.h>
@@ -325,19 +327,10 @@ static void set_fdtfile(void)
 	env_set("fdtfile", fdtfile);
 }
 
-/*
+/* Allow U-Boot to use its control FDT with extlinux if one is not provided */
- * If the firmware provided a valid FDT at boot time, let's expose it in
- * ${fdt_addr} so it may be passed unmodified to the kernel.
- */
 static void set_fdt_addr(void)
 {
-	if (env_get("fdt_addr"))
+	env_set_hex("fdt_addr", (ulong)gd->fdt_blob);
-		return;
-
-	if (fdt_magic(fw_dtb_pointer) != FDT_MAGIC)
-		return;
-
-	env_set_hex("fdt_addr", fw_dtb_pointer);
 }
 
 /*
@@ -572,7 +565,10 @@ int ft_board_setup(void *blob, struct bd_info *bd)
 {
 	int node;
 
-	update_fdt_from_fw(blob, (void *)fw_dtb_pointer);
+	if (blob == gd->fdt_blob)
+		log_debug("Same FDT: nothing to do\n");
+	else
+		update_fdt_from_fw(blob, (void *)gd->fdt_blob);
 
 	node = fdt_node_offset_by_compatible(blob, -1, "simple-framebuffer");
 	if (node < 0)

board/raspberrypi/rpi/rpi.env

@@ -69,9 +69,11 @@ fdt_high=ffffffff
 initrd_high=ffffffff
 #endif
 kernel_addr_r=0x00080000
-scriptaddr=0x02400000
+kernel_comp_addr_r=0x02000000
-pxefile_addr_r=0x02500000
+kernel_comp_size=0x02000000
-fdt_addr_r=0x02600000
+scriptaddr=0x05400000
-ramdisk_addr_r=0x02700000
+pxefile_addr_r=0x05500000
+fdt_addr_r=0x05600000
+ramdisk_addr_r=0x05700000
 
 boot_targets=mmc usb pxe dhcp

common/board_f.c

@@ -553,8 +553,10 @@ static int reserve_fdt(void)
 		 * section, then it will be relocated with other data.
 		 */
 		if (gd->fdt_blob) {
-			gd->boardf->fdt_size =
+			int size = fdt_totalsize(gd->fdt_blob);
-				ALIGN(fdt_totalsize(gd->fdt_blob), 32);
+
+			gd->boardf->fdt_size = ALIGN(size + CONFIG_OF_EXPAND,
+						     32);
 
 			gd->start_addr_sp = reserve_stack_aligned(
 				gd->boardf->fdt_size);

dts/Kconfig

@@ -219,6 +219,17 @@ config OF_OMIT_DTB
 	  This is used for boards which normally provide a devicetree via a
 	  runtime mechanism (such as OF_BOARD), to avoid confusion.
 
+config OF_EXPAND
+	hex # "Amount to allow the control FDT to expand"
+	default SYS_FDT_PAD if OF_LIBFDT
+	default 0
+	help
+	  Some boards make use of the control FDT to boot an OS, thus when
+	  image_setup_libfdt() adds extra things to the end of the FDT, there
+	  needs to be enough space.
+
+	  Set this to the number of bytes of extra space required for the FDT.
+
 config DEFAULT_DEVICE_TREE
 	string "Default Device Tree for DT control"
 	depends on OF_CONTROL