[yocto] rdepend for a kernel recipe

[Jacob Chen]

Hi all,

I have two recipes.

kernel :
https://github.com/rockchip-linux/meta-rockchip/blob/morty/recipes-kernel/linux/linux-mainline_4.11.bb
and kernel module:
https://github.com/rockchip-linux/meta-rockchip/blob/morty/recipes-kernel/linux-extra/rockchip-forwardports_4.11.bb

I want that if I set "PREFERRED_PROVIDER_virtual / kernel" to
"linux-mainline", then  "rockchip-forwardports" will be automatically
installed in my rootfs.

I have set  "RDEPENDS_${PN} += "rockchip-forwardports"" in kernel, but
it didn't work. How can I slove it?

Are there some ways i can do in kernel recipe or image recipe?