Autonegoziation problem (wrt1900acs)

I have a Technicolor modem that connects to my router (wrt1900acs) with 100 mega ethernet speed...
The actual speed is 1 giga... If i try to connect it with my pc directly to the modem, the modem assign 1 giga ethernet speed... Problem is with the router then...
From the log i can see that it connects to the modem with 1 giga...
What could be the problem? Any idea?

i have installed the marvell switch driver.