[PATCH v3 5/5] rpi: Use the U-Boot control FDT for fdt_addr

[Simon Glass <sjg@chromium.org>]

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.

In version 2, it incorporates some changes to fdt_addr, etc. suggested
by Tom, as well as adding myself as a maintainer.

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

(no changes since v2)

Changes in v2:
- Drop patch to allow expanding the devicetree during relocation

 board/raspberrypi/rpi/rpi.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index 9122f33d88d..8f6ab1b1b9b 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/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);
 }
 
-/*
- * 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.
- */
+/* Allow U-Boot to use its control FDT with extlinux if one is not provided */
 static void set_fdt_addr(void)
 {
-	if (env_get("fdt_addr"))
-		return;
-
-	if (fdt_magic(fw_dtb_pointer) != FDT_MAGIC)
-		return;
-
-	env_set_hex("fdt_addr", fw_dtb_pointer);
+	env_set_hex("fdt_addr", (ulong)gd->fdt_blob);
 }
 
 /*
@@ -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)
-- 
2.34.1