i have a dsl router hg630 v2 and another router hg556a which has openwrt installed on it
i want to use adsl router as a bridge and use hg556a as main router as i noticed that
hg630 v2 has lower bandwidth and efficacy ( i received from isp provider and cannot install openwrt on it ) and cannot use hg556a only as openwrt it doesn't support adsl of it
There is, in fact, a very small number of xDSL devices supported, due to driver-related issues, and even some of them have no xDSL modem support in OpenWrt for the same reason.
Your best bet would be to do what @mikma said: put your ISP DSL modem-router in bridge mode (when it functions only as DSL modem), and let your OpenWrt do the rest (i.e. router, switch and AP).
It goes without saying that in this scenario you would need to set-up your OpenWrt WAN connection as PPPoE, entering your ISP username and password there. You may also need to set your MTU on your OpenWrt router. You should find it in your current ISP router setup.