doc: mention that extlinux.conf can use environment in "append"
This option is very useful for A/B boot setups with read-only
filesystems: Letting U-Boot fill in the rootfs (and possibly related
parameters) allows keeping all boot parameters except the actual slot
selection in the extlinux.conf file, where they can be updated easily.
Signed-off-by: Fiona Klute <fiona.klute@gmx.de>
Cc: Tom Rini <trini@konsulko.com>
diff --git a/doc/README.pxe b/doc/README.pxe
index 9fff2cd..ba18908 100644
--- a/doc/README.pxe
+++ b/doc/README.pxe
@@ -178,7 +178,8 @@
kaslrseed - set this label to request random number from hwrng as kaslr seed.
append <string> - use <string> as the kernel command line when booting this
- label.
+ label. Environment variable references like ${var} are
+ substituted before boot.
initrd <path> - if this label is chosen, use tftp to retrieve the initrd
at <path>. it will be stored at the address indicated in