mac80211: make software rate control optional

Some devices implement the entire rate control in
firmware in some way, like wl1271 or like iwlwifi
which does some things in software but not a lot.
Therefore generic software rate control is rather
useless for them and just adds avoidable overhead
to the transmit path.

It's fairly simple to let drivers indicate that
they do not need rate control, but they need to
fulfil a number of conditions that we encode in
WARN_ONs.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/mac80211.h

@@ -855,6 +855,19 @@ enum ieee80211_tkip_key_type {
  * any particular flags. There are some exceptions to this rule,
  * however, so you are advised to review these flags carefully.
  *
+ * @IEEE80211_HW_HAS_RATE_CONTROL:
+ *	The hardware or firmware includes rate control, and cannot be
+ *	controlled by the stack. As such, no rate control algorithm
+ *	should be instantiated, and the TX rate reported to userspace
+ *	will be taken from the TX status instead of the rate control
+ *	algorithm.
+ *	Note that this requires that the driver implement a number of
+ *	callbacks so it has the correct information, it needs to have
+ *	the @set_rts_threshold callback and must look at the BSS config
+ *	@use_cts_prot for G/N protection, @use_short_slot for slot
+ *	timing in 2.4 GHz and @use_short_preamble for preambles for
+ *	CCK frames.
+ *
  * @IEEE80211_HW_RX_INCLUDES_FCS:
  *	Indicates that received frames passed to the stack include
  *	the FCS at the end.
@@ -913,6 +926,7 @@ enum ieee80211_tkip_key_type {
  *	avoid waking up cpu.
  */
 enum ieee80211_hw_flags {
+	IEEE80211_HW_HAS_RATE_CONTROL			= 1<<0,
 	IEEE80211_HW_RX_INCLUDES_FCS			= 1<<1,
 	IEEE80211_HW_HOST_BROADCAST_PS_BUFFERING	= 1<<2,
 	IEEE80211_HW_2GHZ_SHORT_SLOT_INCAPABLE		= 1<<3,

net/mac80211/debugfs.c

@@ -52,7 +52,7 @@ DEBUGFS_READONLY_FILE(total_ps_buffered, 20, "%d",
 DEBUGFS_READONLY_FILE(wep_iv, 20, "%#08x",
 		      local->wep_iv & 0xffffff);
 DEBUGFS_READONLY_FILE(rate_ctrl_alg, 100, "%s",
-		      local->rate_ctrl ? local->rate_ctrl->ops->name : "<unset>");
+	local->rate_ctrl ? local->rate_ctrl->ops->name : "hw/driver");
 
 static ssize_t tsf_read(struct file *file, char __user *user_buf,
 			     size_t count, loff_t *ppos)

net/mac80211/rate.c

@@ -284,9 +284,16 @@ int ieee80211_init_rate_ctrl_alg(struct ieee80211_local *local,
 	struct rate_control_ref *ref, *old;
 
 	ASSERT_RTNL();
+
 	if (local->open_count)
 		return -EBUSY;
 
+	if (local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL) {
+		if (WARN_ON(!local->ops->set_rts_threshold))
+			return -EINVAL;
+		return 0;
+	}
+
 	ref = rate_control_alloc(name, local);
 	if (!ref) {
 		printk(KERN_WARNING "%s: Failed to select rate control "
@@ -305,7 +312,6 @@ int ieee80211_init_rate_ctrl_alg(struct ieee80211_local *local,
 	       "algorithm '%s'\n", wiphy_name(local->hw.wiphy),
 	       ref->ops->name);
 
-
 	return 0;
 }
 
@@ -314,6 +320,10 @@ void rate_control_deinitialize(struct ieee80211_local *local)
 	struct rate_control_ref *ref;
 
 	ref = local->rate_ctrl;
+
+	if (!ref)
+		return;
+
 	local->rate_ctrl = NULL;
 	rate_control_put(ref);
 }

net/mac80211/rate.h

@@ -59,6 +59,9 @@ static inline void rate_control_rate_init(struct sta_info *sta)
 	void *priv_sta = sta->rate_ctrl_priv;
 	struct ieee80211_supported_band *sband;
 
+	if (!ref)
+		return;
+
 	sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 
 	ref->ops->rate_init(ref->priv, sband, ista, priv_sta);
@@ -72,7 +75,7 @@ static inline void rate_control_rate_update(struct ieee80211_local *local,
 	struct ieee80211_sta *ista = &sta->sta;
 	void *priv_sta = sta->rate_ctrl_priv;
 
-	if (ref->ops->rate_update)
+	if (ref && ref->ops->rate_update)
 		ref->ops->rate_update(ref->priv, sband, ista,
 				      priv_sta, changed);
 }
@@ -97,7 +100,7 @@ static inline void rate_control_add_sta_debugfs(struct sta_info *sta)
 {
 #ifdef CONFIG_MAC80211_DEBUGFS
 	struct rate_control_ref *ref = sta->rate_ctrl;
-	if (sta->debugfs.dir && ref->ops->add_sta_debugfs)
+	if (ref && sta->debugfs.dir && ref->ops->add_sta_debugfs)
 		ref->ops->add_sta_debugfs(ref->priv, sta->rate_ctrl_priv,
 					  sta->debugfs.dir);
 #endif
@@ -107,7 +110,7 @@ static inline void rate_control_remove_sta_debugfs(struct sta_info *sta)
 {
 #ifdef CONFIG_MAC80211_DEBUGFS
 	struct rate_control_ref *ref = sta->rate_ctrl;
-	if (ref->ops->remove_sta_debugfs)
+	if (ref && ref->ops->remove_sta_debugfs)
 		ref->ops->remove_sta_debugfs(ref->priv, sta->rate_ctrl_priv);
 #endif
 }

net/mac80211/sta_info.c

@@ -148,8 +148,10 @@ struct sta_info *sta_info_get_by_idx(struct ieee80211_sub_if_data *sdata,
 static void __sta_info_free(struct ieee80211_local *local,
 			    struct sta_info *sta)
 {
+	if (sta->rate_ctrl) {
 		rate_control_free_sta(sta);
 		rate_control_put(sta->rate_ctrl);
+	}
 
 #ifdef CONFIG_MAC80211_VERBOSE_DEBUG
 	printk(KERN_DEBUG "%s: Destroyed STA %pM\n",
@@ -277,6 +279,23 @@ static void sta_unblock(struct work_struct *wk)
 		ieee80211_sta_ps_deliver_poll_response(sta);
 }
 
+static int sta_prepare_rate_control(struct ieee80211_local *local,
+				    struct sta_info *sta, gfp_t gfp)
+{
+	if (local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL)
+		return 0;
+
+	sta->rate_ctrl = rate_control_get(local->rate_ctrl);
+	sta->rate_ctrl_priv = rate_control_alloc_sta(sta->rate_ctrl,
+						     &sta->sta, gfp);
+	if (!sta->rate_ctrl_priv) {
+		rate_control_put(sta->rate_ctrl);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
 struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 				u8 *addr, gfp_t gfp)
 {
@@ -296,11 +315,7 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 	sta->local = local;
 	sta->sdata = sdata;
 
-	sta->rate_ctrl = rate_control_get(local->rate_ctrl);
-	sta->rate_ctrl_priv = rate_control_alloc_sta(sta->rate_ctrl,
-						     &sta->sta, gfp);
-	if (!sta->rate_ctrl_priv) {
-		rate_control_put(sta->rate_ctrl);
+	if (sta_prepare_rate_control(local, sta, gfp)) {
 		kfree(sta);
 		return NULL;
 	}

net/mac80211/tx.c

@@ -1219,6 +1219,7 @@ static int invoke_tx_handlers(struct ieee80211_tx_data *tx)
 	CALL_TXH(ieee80211_tx_h_ps_buf);
 	CALL_TXH(ieee80211_tx_h_select_key);
 	CALL_TXH(ieee80211_tx_h_michael_mic_add);
+	if (!(tx->local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL))
 		CALL_TXH(ieee80211_tx_h_rate_ctrl);
 	CALL_TXH(ieee80211_tx_h_misc);
 	CALL_TXH(ieee80211_tx_h_sequence);