common/image.c: align usage of fdt_high with initrd_high
The commit message of a28afca (Add uboot "fdt_high" enviroment variable)
states that fdt_high behaves similarly to the existing initrd_high.
But fdt_high actually has an outstanding difference from initrd_high.
The former specifies the start address, while the later specifies the
end address.
As fdt_high and initrd_high will likely be used together, it'd be nice
to have them behave same. The patch changes the behavior of fdt_high
to have it aligned with initrd_high.
The document of fdt_high in README is updated with an example to
demonstrate the usage of this environment variable.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index eba6378..8964672 100644
--- a/README
+++ b/README
@@ -3665,6 +3665,14 @@
fdt_high - if set this restricts the maximum address that the
flattened device tree will be copied into upon boot.
+ For example, if you have a system with 1 GB memory
+ at physical address 0x10000000, while Linux kernel
+ only recognizes the first 704 MB as low memory, you
+ may need to set fdt_high as 0x3C000000 to have the
+ device tree blob be copied to the maximum address
+ of the 704 MB low memory, so that Linux kernel can
+ access it during the boot procedure.
+
If this is set to the special value 0xFFFFFFFF then
the fdt will not be copied at all on boot. For this
to work it must reside in writable memory, have