Hi Masahiro
As indicated into doc/README.fdt-control, it's possible build U-boot with specifying dts-file-name using $ make DEVICE_TREE=<dts-file-name> But since your commit a3444bd09af9 ("Revert "Ensure device tree DTS is compiled") it's no more possible:
make ARCH=arm CROSS_COMPILE=$CROSS_COMPILE -j 16 DEVICE_TREE="trial"
Device Tree Source is not correctly specified. Please define 'CONFIG_DEFAULT_DEVICE_TREE' or build with 'DEVICE_TREE=<device_tree>' argument
dts/Makefile:28: recipe for target 'arch/arm/dts/trial.dtb' failed make[1]: *** [arch/arm/dts/trial.dtb] Error 1 Makefile:1087: recipe for target 'dts/dt.dtb' failed make: *** [dts/dt.dtb] Error 2
By reverting the above patch, it's restoring the attended behavior. But In your commit you indicated several issues.
Unfortunately, i am not a Makefile "expert", can anybody have a look at it ?
Thanks
Patrice