sandbox whith oftree on making error

[zzs]

my code baseed 7423f13

when making sandox with command oftree on then I got the flowwing
build error:

CC      drivers/of/gpio.o
In file included from /home/zzs/work/repos/barebox/drivers/of/gpio.c:6:0:
/home/zzs/work/repos/barebox/include/gpio.h:4:22: fatal error: asm/gpio.h: No such file or directory
compilation terminated.
make[3]: *** [drivers/of/gpio.o] Error 1
make[2]: *** [drivers/of] Error 2
make[1]: *** [drivers] Error 2
make: *** [_all] Error 2

My building commandline like this:
    CROSS_COMPILE= ARCH=sandbox make O=objtree sandbox_defconfig
    CROSS_COMPILE= ARCH=sandbox make O=objtree xconfig
        .... turn oftree on
    CROSS_COMPILE= ARCH=sandbox make O=objtree

I think this is a bug

-- 
Best Regards,
zzs