rtwn: add a default OFDM / CCK rate for self-generated frames

I noticed during testing that the MAC was generating MCS7 ACKs and
MCS7 block-ACK frames in response to MCS frames from its peer.
This is very suboptimal - it means that unless you're very close
to your peer (in this case a 2GHz AP), you'll end up failing a lot
of ACKs.

Linux faced the opposite problem in rtl8xxxu - the rate set being
programmed in here included a lot MORE rates, including MCS 0->7
and OFDM 6M->54M.  This meant that they were INTENTIONALLY telling
the hardware to transmit at higher rates, and their fix was to
mask out the higher rates so self-generated frames don't try the
high rates at all.

Now, I am not sure why I'm not seeing any OFDM or HT basic rates.
We don't mark any OFDM / HT rates as basic in net80211 (in
ieee80211_phy.c) so I'm going to need to go and do a review of the
standard to see what's up.  Additionally, the HT rate set that we
populate isn't tagging any of the HT rates as IEEE80211_RATE_BASIC,
so the code I added for now is a no-op.

So:

* Extend rtwn_get_rates() and its consumers to populate the HT rateset
  with basic rates if they're provided
* Add a default 2GHz / 5GHz mask, inspired by linux, applied over the
  basic rates provided.
* Make sure there's at least an OFDM rate (for 2G/5G) rate available if
  the peer node is HT, which avoids the MAC defaulting to MCS7 when
  generating ACK/block-ACK.
* Add register definitions for INIDATA/INIRTS, which set the default
  data rate when the driver doesn't specify the initial data / RTS/CTS
  rates in the TX descriptor.
* Leave a comment about why I've modified the mask from Linux.

Locally tested:

* RTL8192CU, STA mode
* RTL8188EU, STA mode
* RTL8192EU, STA mode
* RTL8812AU, STA mode

Differential Revision:	https://reviews.freebsd.org/D48019
Reviewed by:	bz

1 files changed, 34 insertions, 4 deletions

diff --git a/sys/dev/rtwn/if_rtwn.c b/sys/dev/rtwn/if_rtwn.c
index be01ececf307..3b286d9adba9 100644
--- a/sys/dev/rtwn/if_rtwn.c
+++ b/sys/dev/rtwn/if_rtwn.c
@@ -1202,7 +1202,8 @@ rtwn_calc_basicrates(struct rtwn_softc *sc)
 		struct rtwn_vap *rvp;
 		struct ieee80211vap *vap;
 		struct ieee80211_node *ni;
-		uint32_t rates;
+		struct ieee80211_htrateset *rs_ht;
+		uint32_t rates = 0, htrates = 0;
 
 		rvp = sc->vaps[i];
 		if (rvp == NULL || rvp->curr_mode == R92C_MSR_NOLINK)
@@ -1213,16 +1214,45 @@ rtwn_calc_basicrates(struct rtwn_softc *sc)
 			continue;
 
 		ni = ieee80211_ref_node(vap->iv_bss);
-		/* Only fetches basic rates; no need to add HT/VHT here */
-		rtwn_get_rates(sc, &ni->ni_rates, NULL, &rates, NULL, NULL, 1);
+		if (ni->ni_flags & IEEE80211_NODE_HT)
+			rs_ht = &ni->ni_htrates;
+		else
+			rs_ht = NULL;
+		/*
+		 * Only fetches basic rates; fetch 802.11abg and 11n basic
+		 * rates
+		 */
+		rtwn_get_rates(sc, &ni->ni_rates, rs_ht, &rates, &htrates,
+		    NULL, 1);
+
+		/*
+		 * We need at least /an/ OFDM and/or MCS rate for HT
+		 * operation, or the MAC will generate MCS7 ACK/Block-ACK
+		 * frames and thus performance will suffer.
+		 */
+		if (ni->ni_flags & IEEE80211_NODE_HT) {
+			htrates |= 0x01; /* MCS0 */
+			rates |= (1 << RTWN_RIDX_OFDM6);
+		}
+
 		basicrates |= rates;
+		basicrates |= (htrates << RTWN_RIDX_HT_MCS_SHIFT);
+
+		/* Filter out undesired high rates */
+		if (ni->ni_chan != IEEE80211_CHAN_ANYC &&
+		    IEEE80211_IS_CHAN_5GHZ(ni->ni_chan))
+			basicrates &= R92C_RRSR_RATE_MASK_5GHZ;
+		else
+			basicrates &= R92C_RRSR_RATE_MASK_2GHZ;
+
 		ieee80211_free_node(ni);
 	}
 
+
 	if (basicrates == 0)
 		return;
 
-	/* XXX initial RTS rate? */
+	/* XXX also set initial RTS rate? */
 	rtwn_set_basicrates(sc, basicrates);
 }