Problem reloading a GP timer kernel module on the xm

Hey all, I’m fairly new to Linux kernel module development, so I apologize in advance if I’m missing something really obvious here. I’m trying to write a simple module using the OMAP3730’s GP timer in order to benchmark/timestamp with more resolution.

The relevant code looks like this:

static struct omap_dm_timer *timer_ptr; // Global timer

static int hrt_init(void)
int result = 0;

printk(“hrt: inserting module\n”);

/* Register device with our requested major */
result = register_chrdev(hrt_major, “hrt”, &hrt_fops);
if (result < 0) {
printk(“hrt: error: can’t obtain major number %d\n”, hrt_major);
return result;

/* Reserve a timer */
timer_ptr = omap_dm_timer_request();

if (timer_ptr == NULL){
printk(“hrt: error: no timer is available\n”);
return -1;

/* Set clock source to system clock, prescaler to 1:1, start the timer */
if (omap_dm_timer_set_source(timer_ptr, OMAP_TIMER_SRC_SYS_CLK) < 0)
printk(“hrt: error setting OPMAP_TIMER_SRC_SYS_CLK\n”);
return -1;
omap_dm_timer_set_prescaler(timer_ptr, 0);
omap_dm_timer_set_load_start(timer_ptr, 1, 0);

/* Success */
return 0;

static void hrt_exit(void)
printk(“hrt: removing module\n”);

/* Stop and release the timer */
timer_ptr = 0;

/* Unregister the char device */
unregister_chrdev(hrt_major, “hrt”);


I’m compiling under Angstrom on

Linux beagleboard 3.6.7+ #1 SMP armv7l GNU/Linux


The first time I insert the module, it works fine. I can also remove it, and verify that the hrt_exit() function is run in the log. The problem comes when I try to re-insert it, and consequently re-allocate a timer. I get the following from the kernel:


[ 2546.762268] hrt: inserting module
[ 2546.765960] omap_dm_timer_set_source: failed to set timer_32k_ck as parent
[ 2546.773345] hrt: error: no timer is available
insmod: error inserting ‘HRT.ko’: -1 Operation not permitted


I haven’t been able to find any info around the web on this particular error, I’m a little confused because I’m not trying to set_source until after I allocate the timer, but that message appears before the allocation failure error. In any case, I don’t see why it is failing to allocate another timer, especially given that there are several on the SoC. Any ideas? Need more info? Thank you!