Make mira cope with out-of-range single frame error rate (SFER) values.

These are either due to driver bugs or rounding errors in fixed point math
but can be dealt with gracefully and don't occur often (only one instance
of this problem has been reported in the wild so far).

Turn related panics into debug printfs.
With 'ifconfig athn0 debug' the kernel now prints notifications about
out-of-range SFER values in dmesg. Compile a kernel with 'option MIRA_DEBUG'
to get a dump of driver stats in dmesg as well.

This change should prevent an undesirable panic reported by Peter Kay,
though it does not actually address the root cause of the problem.

ok tb@

1 files changed, 41 insertions, 12 deletions

diff --git a/sys/net80211/ieee80211_mira.c b/sys/net80211/ieee80211_mira.c
index 0ca11234e33..1b261b04e15 100644
--- a/sys/net80211/ieee80211_mira.c
+++ b/sys/net80211/ieee80211_mira.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_mira.c,v 1.9 2017/01/28 11:57:19 stsp Exp $	*/
+/*	$OpenBSD: ieee80211_mira.c,v 1.10 2017/01/28 16:01:36 stsp Exp $	*/
 
 /*
  * Copyright (c) 2016 Stefan Sperling <stsp@openbsd.org>
@@ -136,6 +136,17 @@ mira_fp_sprintf(uint64_t fp)
 
 	return buf;
 }
+
+void
+mira_print_driver_stats(struct ieee80211_mira_node *mn,
+    struct ieee80211_node *ni) {
+	DPRINTF(("%s driver stats:\n", ether_sprintf(ni->ni_macaddr)));
+	DPRINTF(("mn->frames = %u\n", mn->frames));
+	DPRINTF(("mn->retries = %u\n", mn->retries));
+	DPRINTF(("mn->txfail = %u\n", mn->txfail));
+	DPRINTF(("mn->ampdu_size = %u\n", mn->ampdu_size));
+	DPRINTF(("mn->agglen = %u\n", mn->agglen));
+}
 #endif /* MIRA_DEBUG */
 
 /*
@@ -428,12 +439,33 @@ ieee80211_mira_update_stats(struct ieee80211_mira_node *mn,
 
 	/* Compute Sub-Frame Error Rate (see section 2.2 in MiRA paper). */
 	sfer = (mn->frames * mn->retries + mn->txfail);
-	if ((sfer >> MIRA_FP_SHIFT) != 0)
-		panic("sfer overflow"); /* bug in wifi driver */
+	if ((sfer >> MIRA_FP_SHIFT) != 0) { /* bug in wifi driver */
+		if (ic->ic_if.if_flags & IFF_DEBUG) {
+#ifdef DIAGNOSTIC
+			printf("%s: mira sfer overflow\n",
+			    ether_sprintf(ni->ni_macaddr));
+#endif
+#ifdef MIRA_DEBUG
+			mira_print_driver_stats(mn, ni);
+#endif
+		}
+		ieee80211_mira_probe_done(mn);
+		return;
+	}
 	sfer <<= MIRA_FP_SHIFT; /* convert to fixed-point */
 	sfer /= ((mn->retries + 1) * mn->frames);
-	if (sfer > MIRA_FP_1)
-		panic("sfer > 1"); /* bug in wifi driver */
+	if (sfer > MIRA_FP_1) { /* bug in wifi driver */
+		if (ic->ic_if.if_flags & IFF_DEBUG) {
+#ifdef DIAGNOSTIC
+			printf("%s: mira sfer > 1\n",
+			    ether_sprintf(ni->ni_macaddr));
+#endif
+#ifdef MIRA_DEBUG
+			mira_print_driver_stats(mn, ni);
+#endif
+		}
+		sfer = MIRA_FP_1; /* round down */
+	}
 
 	/* Store current loss percentage SFER. */
 	g->loss = sfer * 100;
@@ -1004,13 +1036,10 @@ ieee80211_mira_choose(struct ieee80211_mira_node *mn, struct ieee80211com *ic,
 	if (mn->valid_rates == 0)
 		mn->valid_rates = ieee80211_mira_valid_rates(ic, ni);
 
-	DPRINTFN(5, ("%s: driver stats:\n", __func__));
-	DPRINTFN(5, ("mn->frames = %u\n", mn->frames));
-	DPRINTFN(5, ("mn->retries = %u\n", mn->retries));
-	DPRINTFN(5, ("mn->txfail = %u\n", mn->txfail));
-	DPRINTFN(5, ("mn->ampdu_size = %u\n", mn->ampdu_size));
-	DPRINTFN(5, ("mn->agglen = %u\n", mn->agglen));
-
+#ifdef MIRA_DEBUG
+	if (mira_debug >= 5)
+		mira_print_driver_stats(mn, ni);
+#endif
 	ieee80211_mira_update_stats(mn, ic, ni);
 
 	if (mn->probing) {