From: IanR778 <IanR778@users.noreply.github.com>
Date: Wed, 8 Oct 2014 20:00:37 +0000 (+0100)
Subject: FIX: support rstamps from the future too.
X-Git-Tag: 1.4.0~1^2~1
X-Git-Url: https://jxself.org/git/?a=commitdiff_plain;h=07a2fecf33ddaf1e497fa9118458f71230dc0032;p=open-ath9k-htc-firmware.git

FIX: support rstamps from the future too.

 * Extend a 32 bit TSF to nearest 64 bit TSF value.
 * When the adapter is a STATION, its local TSF is periodically modified by
 * the hardware to match the BSS TSF (as received in beacon packets), and
 * rstamp may appear to be from the future or from the past (with reference
 * to the current local TSF) because of jitter. This is mostly noticable in
 * highly congested channels. The code uses signed modulo arithmetic to
 * handle both past/future cases and signed-extension to avoid branches.
 * Test cases:
 * extend(0x0000001200000004, 0x00000006) == 0x0000001200000006
 * extend(0x0000001200000004, 0x00000002) == 0x0000001200000002
 * extend(0x0000001200000004, 0xfffffffe) == 0x00000011fffffffe  ! tsfhigh--
 * extend(0x00000012fffffffc, 0xfffffffe) == 0x00000012fffffffe
 * extend(0x00000012fffffffc, 0xfffffffa) == 0x00000012fffffffa
 * extend(0x00000012fffffffc, 0x00000002) == 0x0000001300000002  ! tsfhigh++
---

diff --git a/target_firmware/wlan/if_ath.c b/target_firmware/wlan/if_ath.c
index 206b5c0..78a02e1 100755
--- a/target_firmware/wlan/if_ath.c
+++ b/target_firmware/wlan/if_ath.c
@@ -82,19 +82,34 @@ void ath_tgt_tx_sched_normal(struct ath_softc_tgt *sc, struct ath_buf *bf);
 void ath_tgt_tx_sched_nonaggr(struct ath_softc_tgt *sc,struct ath_buf * bf_host);
 
 /*
- * Extend a 32 bit TSF to 64 bit, taking wrapping into account.
+ * Extend a 32 bit TSF to nearest 64 bit TSF value.
+ * When the adapter is a STATION, its local TSF is periodically modified by
+ * the hardware to match the BSS TSF (as received in beacon packets), and
+ * rstamp may appear to be from the future or from the past (with reference
+ * to the current local TSF) because of jitter. This is mostly noticable in
+ * highly congested channels. The code uses signed modulo arithmetic to
+ * handle both past/future cases and signed-extension to avoid branches.
+ * Test cases:
+ * extend(0x0000001200000004, 0x00000006) == 0x0000001200000006
+ * extend(0x0000001200000004, 0x00000002) == 0x0000001200000002
+ * extend(0x0000001200000004, 0xfffffffe) == 0x00000011fffffffe  ! tsfhigh--
+ * extend(0x00000012fffffffc, 0xfffffffe) == 0x00000012fffffffe
+ * extend(0x00000012fffffffc, 0xfffffffa) == 0x00000012fffffffa
+ * extend(0x00000012fffffffc, 0x00000002) == 0x0000001300000002  ! tsfhigh++
  */
 static u_int64_t ath_extend_tsf(struct ath_softc_tgt *sc, u_int32_t rstamp)
 {
 	struct ath_hal *ah = sc->sc_ah;
 	u_int64_t tsf;
+	a_int32_t tsf_low;
+	a_int64_t tsf_delta;  /* signed int64 */
 
 	tsf = ah->ah_getTsf64(ah);
+	tsf_low = tsf & 0xffffffff;
 
-	if (rstamp > (tsf & 0xffffffffULL))
-		tsf -= 0x100000000ULL;
+	tsf_delta = (a_int32_t)rstamp - (a_int64_t)tsf_low;
 
-	return ((tsf & ~0xffffffffULL) | rstamp);
+	return (tsf + (u_int64_t)tsf_delta);
 }
 
 static a_int32_t ath_rate_setup(struct ath_softc_tgt *sc, a_uint32_t mode)