boot: pxe_utils: skip fdt setup in case legacy kernel is booted
Currently, if boot with extlinux.conf and do not set the fdt
U-Boot will provide its own device tree. This behavior is
beneficial if the U-Boot device tree is in sync with Linux,
but it totally halts the booting of pre-dtb kernels (3.4 for
example) since it uses ATAGs. To fix this, pass `-` in the
fdt extlinux field as a signal that no tree should be used.
Suggested-by: Jonas Schwöbel <jonasschwoebel@yahoo.de>
Tested-by: Jethro Bull <jethrob@hotmail.com>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/doc/develop/distro.rst b/doc/develop/distro.rst
index 8016aca..9e715b2 100644
--- a/doc/develop/distro.rst
+++ b/doc/develop/distro.rst
@@ -81,6 +81,12 @@
* Does not document the fdtdir option, which automatically selects the DTB to
pass to the kernel.
+* If no fdt/fdtdir is provided, the U-Boot will pass its own currently used
+ device tree.
+
+* If ``-`` is passed as fdt argument and ``CONFIG_SUPPORT_PASSING_ATAGS`` is
+ enabled, then no device tree will be used (legacy booting / pre-dtb kernel).
+
See also doc/README.pxe under 'pxe file format'.
One example extlinux.conf generated by the Fedora installer is::