ath9k: Do not update frame's duration field

When AR_DurUpdateEna is set, the frame's duration field
is updated by the MAC based on the current rate.
Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath9k/core.h

@@ -516,7 +516,6 @@ struct ath_tx_control {
 	u32 keyix;
 	int min_rate;
 	int mcast_rate;
-	u16 nextfraglen;
 	struct ath_softc *dev;
 	dma_addr_t dmacontext;
 };

drivers/net/wireless/ath9k/xmit.c

@@ -227,7 +227,6 @@ static int ath_tx_prepare(struct ath_softc *sc,
 	}
 
 	txctl->if_id = 0;
-	txctl->nextfraglen = 0;
 	txctl->frmlen = skb->len + FCS_LEN - (hdrlen & 3);
 	txctl->txpower = MAX_RATE_POWER; /* FIXME */
 
@@ -344,36 +343,6 @@ static int ath_tx_prepare(struct ath_softc *sc,
 	}
 	rix = rcs[0].rix;
 
-	/*
-	 * Calculate duration.  This logically belongs in the 802.11
-	 * layer but it lacks sufficient information to calculate it.
-	 */
-	if ((txctl->flags & ATH9K_TXDESC_NOACK) == 0 && !ieee80211_is_ctl(fc)) {
-		u16 dur;
-		/*
-		 * XXX not right with fragmentation.
-		 */
-		if (sc->sc_flags & SC_OP_PREAMBLE_SHORT)
-			dur = rt->info[rix].spAckDuration;
-		else
-			dur = rt->info[rix].lpAckDuration;
-
-		if (le16_to_cpu(hdr->frame_control) &
-				IEEE80211_FCTL_MOREFRAGS) {
-			dur += dur;  /* Add additional 'SIFS + ACK' */
-
-			/*
-			** Compute size of next fragment in order to compute
-			** durations needed to update NAV.
-			** The last fragment uses the ACK duration only.
-			** Add time for next fragment.
-			*/
-			dur += ath9k_hw_computetxtime(sc->sc_ah, rt,
-				      txctl->nextfraglen,
-				      rix,
-				      (sc->sc_flags & SC_OP_PREAMBLE_SHORT));
-		}
-
 	if (ieee80211_has_morefrags(fc) ||
 	    (le16_to_cpu(hdr->seq_ctrl) & IEEE80211_SCTL_FRAG)) {
 		/*
@@ -388,9 +357,6 @@ static int ath_tx_prepare(struct ath_softc *sc,
 		rcs[0].tries = ATH_TXMAXTRY;
 	}
 
-		hdr->duration_id = cpu_to_le16(dur);
-	}
-
 	/*
 	 * Determine if a tx interrupt should be generated for
 	 * this descriptor.  We take a tx interrupt to reap