Function tc_init

freebsd/kern/kern_tc.c:1155–1218

* Initialize a new timecounter and possibly use it. */

 * Initialize a new timecounter and possibly use it.
 */
void
tc_init(struct timecounter *tc)
{
	u_int u;
	struct sysctl_oid *tc_root;

	u = tc->tc_frequency / tc->tc_counter_mask;
	/* XXX: We need some margin here, 10% is a guess */
	u *= 11;
	u /= 10;
	if (u > hz && tc->tc_quality >= 0) {
		tc->tc_quality = -2000;
		if (bootverbose) {
			printf("Timecounter \"%s\" frequency %ju Hz",
			    tc->tc_name, (uintmax_t)tc->tc_frequency);
			printf(" -- Insufficient hz, needs at least %u\n", u);
		}
	} else if (tc->tc_quality >= 0 || bootverbose) {
		printf("Timecounter \"%s\" frequency %ju Hz quality %d\n",
		    tc->tc_name, (uintmax_t)tc->tc_frequency,
		    tc->tc_quality);
	}

	tc->tc_next = timecounters;
	timecounters = tc;
	/*
	 * Set up sysctl tree for this counter.
	 */
	tc_root = SYSCTL_ADD_NODE_WITH_LABEL(NULL,
	    SYSCTL_STATIC_CHILDREN(_kern_timecounter_tc), OID_AUTO, tc->tc_name,
	    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
	    "timecounter description", "timecounter");
	SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
	    "mask", CTLFLAG_RD, &(tc->tc_counter_mask), 0,
	    "mask for implemented bits");
	SYSCTL_ADD_PROC(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
	    "counter", CTLTYPE_UINT | CTLFLAG_RD | CTLFLAG_MPSAFE, tc,
	    sizeof(*tc), sysctl_kern_timecounter_get, "IU",
	    "current timecounter value");
	SYSCTL_ADD_PROC(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
	    "frequency", CTLTYPE_U64 | CTLFLAG_RD | CTLFLAG_MPSAFE, tc,
	    sizeof(*tc), sysctl_kern_timecounter_freq, "QU",
	    "timecounter frequency");
	SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
	    "quality", CTLFLAG_RD, &(tc->tc_quality), 0,
	    "goodness of time counter");
	/*
	 * Do not automatically switch if the current tc was specifically
	 * chosen.  Never automatically use a timecounter with negative quality.
	 * Even though we run on the dummy counter, switching here may be
	 * worse since this timecounter may not be monotonic.
	 */
	if (tc_chosen)
		return;
	if (tc->tc_quality < 0)
		return;
	if (tc->tc_quality < timecounter->tc_quality)
		return;