doc: board: samsung: exynos-mobile: add DEVICE_TREE make flag in build

Since there is only one internal device tree allowed in U-Boot, the
DEVICE_TREE flag is required for building images for various devices.
Document it in the build guide.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

diff --git a/doc/board/samsung/exynos-mobile.rst b/doc/board/samsung/exynos-mobile.rst
index 37718af1feae218efd6201f682b111004e3fc10a..d0173b1f8cb69ae00d6978644b4bc38126701686 100644 (file)
--- a/doc/board/samsung/exynos-mobile.rst
+++ b/doc/board/samsung/exynos-mobile.rst
@@ -25,12 +25,13 @@ If a cross-compiler is required, install it and set it up like so:
 
        export CROSS_COMPILE=aarch64-linux-gnu-
 
-Then, run the following commands to build U-Boot:
+Then, run the following commands to build U-Boot (replace ``<dtb>`` with the
+upstream DTB path for the target device):
 
 .. prompt:: bash $
 
        make O=.output exynos-mobile_defconfig
-       make O=.output -j$(nproc)
+       make DEVICE_TREE=<dtb> O=.output -j$(nproc)
 
 If successful, the U-Boot binary will be present in ``.output/u-boot.bin``.