How to use the OMAP4460 timers on pandaboard android system ?

I just want to use OMAP4460 Timer 11 as a pwm output  on pandaboard .  But , I can 't request it . could someone help . please !

When I used the method below , It just faild .

setpwm(void)

{

struct omap_dm_timer *dm_timer_pdev ;

dm_timer_pdev = omap_dm_timer_request_specific( 11 );

.....

}

I put the setpwm() function to the   board-omap4panada.c  board init function  omap4_panda_init(void) ; 

the omap_dm_timer_request_specific always return NULL ,

Is there something else has to be done before I use the function omap_dm_timer_request_specific( 11 )  ?

thank you !