[PATCH v4 5/5] rpi: Use the U-Boot control FDT for fdt_addr

[Simon Glass]

The fdt_addr variable is used in extlinux as a fallback devicetree if
none is provided by the boot command. Otherwise the only use in U-Boot
seems to me efi_install_fdt() when the internal FDT is required.

The existing mechanism uses the devicetree provided to U-Boot, but in
its original, unrelocated position. In my testing on an rpi_4, this ends
up 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.

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

Changes in v4:
- Expand the comment on set_fdt_addr()
- Update the commit message to talk in terms of my testing

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

 board/raspberrypi/rpi/rpi.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index c46fe4b2350..f74006e0968 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>
@@ -326,18 +328,13 @@ static void set_fdtfile(void)
 }
 
 /*
- * 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.
+ * This will then go through the usual fixups that U-Boot does, before being
+ * handed off to Linux
  */
 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);
 }
 
 /*
@@ -571,7 +568,10 @@ 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