[PATCH v2] docs: Correct FW_JUMP_FDT_ADDR calculation example

[Gabriel Somlo]

When using `PLATFORM=generic` defaults, the kernel is loaded at
`FW_JUMP_ADDR`, and the FDT is loaded at `FW_JUMP_FDT_ADDR.

Therefore, the maximum kernel size before `FW_JUMP_FDT_ADDR` must
be increased is `$(( FW_JUMP_FDT_ADDR - FW_JUMP_ADDR ))`.

The example calculation assumes `rv64`, and is wrong to boot
(off by 0x200000). Fix it and update it for the general case.

Signed-off-by: Gabriel Somlo <gsomlo at gmail.com>
---
 docs/firmware/fw_jump.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/firmware/fw_jump.md b/docs/firmware/fw_jump.md
index 956897e..03ddf96 100644
--- a/docs/firmware/fw_jump.md
+++ b/docs/firmware/fw_jump.md
@@ -48,13 +48,13 @@ follows:
   ```
   ${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 | awk -n '/^ +[0-9]+ /\
   {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}' \
-  | (( `tail -1` > 0x2200000 )) && echo fdt overlaps kernel,\
-  increase FW_JUMP_FDT_ADDR
+  | (( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) && \
+  echo fdt overlaps kernel, increase FW_JUMP_FDT_ADDR
 
   ${LLVM}objdump -h --show-lma $KERNEL_ELF | sort -k 5,5 | \
   awk -n '/^ +[0-9]+ / {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}'\
-  | (( `tail -1` > 0x2200000 )) && echo fdt overlaps kernel,\
-  increase FW_JUMP_FDT_ADDR
+  | (( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) && \
+  echo fdt overlaps kernel, increase FW_JUMP_FDT_ADDR
   ```
 
 *FW_JUMP* Example
-- 
2.39.2