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@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)