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>

MAINTAINERS

@@ -210,7 +210,6 @@ N:	aspeed
 ARM BROADCOM BCM283X / BCM27XX
 M:	Matthias Brugger <mbrugger@suse.com>
 M:	Peter Robinson <pbrobinson@gmail.com>
-M:	Simon Glass <sjg@chromium.org>
 S:	Maintained
 F:	arch/arm/dts/bcm283*
 F:	arch/arm/mach-bcm283x/

board/raspberrypi/rpi/rpi.env

@@ -61,13 +61,13 @@ dfu_alt_info+=zImage fat 0 1
  * only 64M, the remaining 25M starting at 0x02700000 should allow quite
  * large initrds before they start colliding with U-Boot.
  */
-
+#ifdef CONFIG_ARM64
-/*
+fdt_high=ffffffffffffffff
- * limit bootm_size to 512MB so that all boot images stay within the bottom
+initrd_high=ffffffffffffffff
- * 512MB of memory
+#else
- */
+fdt_high=ffffffff
-bootm_size=0x20000000
+initrd_high=ffffffff
-
+#endif
 kernel_addr_r=0x00080000
 kernel_comp_addr_r=0x02000000
 kernel_comp_size=0x02000000

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