mac80211: rework tx encapsulation offload API

The current API (which lets the driver turn on/off per vif directly) has a
number of limitations:
- it does not deal with AP_VLAN
- conditions for enabling (no tkip, no monitor) are only checked at
  add_interface time
- no way to indicate 4-addr support

In order to address this, store offload flags in struct ieee80211_vif
(easy to extend for decap offload later). mac80211 initially sets the enable
flag, but gives the driver a chance to modify it before its settings are
applied. In addition to the .add_interface op, a .update_vif_offload op is
introduced, which can be used for runtime changes.

If a driver can't disable encap offload at runtime, or if it has some extra
limitations, it can simply override the flags within those ops.

Support for encap offload with 4-address mode interfaces can be enabled
by setting a flag from .add_interface or .update_vif_offload.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20200908123702.88454-6-nbd@nbd.name
[resolved conflict with commit aa2092a9ba ("ath11k: add raw mode and
software crypto support")]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -1606,6 +1606,21 @@ enum ieee80211_vif_flags {
 	IEEE80211_VIF_GET_NOA_UPDATE		= BIT(3),
 };
 
+
+/**
+ * enum ieee80211_offload_flags - virtual interface offload flags
+ *
+ * @IEEE80211_OFFLOAD_ENCAP_ENABLED: tx encapsulation offload is enabled
+ *	The driver supports sending frames passed as 802.3 frames by mac80211.
+ *	It must also support sending 802.11 packets for the same interface.
+ * @IEEE80211_OFFLOAD_ENCAP_4ADDR: support 4-address mode encapsulation offload
+ */
+
+enum ieee80211_offload_flags {
+	IEEE80211_OFFLOAD_ENCAP_ENABLED		= BIT(0),
+	IEEE80211_OFFLOAD_ENCAP_4ADDR		= BIT(1),
+};
+
 /**
  * struct ieee80211_vif - per-interface data
  *
@@ -1626,6 +1641,11 @@ enum ieee80211_vif_flags {
  *	these need to be set (or cleared) when the interface is added
  *	or, if supported by the driver, the interface type is changed
  *	at runtime, mac80211 will never touch this field
+ * @offloaad_flags: hardware offload capabilities/flags for this interface.
+ *	These are initialized by mac80211 before calling .add_interface,
+ *	.change_interface or .update_vif_offload and updated by the driver
+ *	within these ops, based on supported features or runtime change
+ *	restrictions.
  * @hw_queue: hardware queue for each AC
  * @cab_queue: content-after-beacon (DTIM beacon really) queue, AP mode only
  * @chanctx_conf: The channel context this interface is assigned to, or %NULL
@@ -1662,6 +1682,7 @@ struct ieee80211_vif {
 	struct ieee80211_chanctx_conf __rcu *chanctx_conf;
 
 	u32 driver_flags;
+	u32 offload_flags;
 
 #ifdef CONFIG_MAC80211_DEBUGFS
 	struct dentry *debugfs_dir;
@@ -2328,6 +2349,9 @@ struct ieee80211_txq {
  *	aggregating MPDUs with the same keyid, allowing mac80211 to keep Tx
  *	A-MPDU sessions active while rekeying with Extended Key ID.
  *
+ * @IEEE80211_HW_SUPPORTS_TX_ENCAP_OFFLOAD: Hardware supports tx encapsulation
+ *	offload
+ *
  * @NUM_IEEE80211_HW_FLAGS: number of hardware flags, used for sizing arrays
  */
 enum ieee80211_hw_flags {
@@ -2380,6 +2404,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_SUPPORTS_MULTI_BSSID,
 	IEEE80211_HW_SUPPORTS_ONLY_HE_MULTI_BSSID,
 	IEEE80211_HW_AMPDU_KEYBORDER_SUPPORT,
+	IEEE80211_HW_SUPPORTS_TX_ENCAP_OFFLOAD,
 
 	/* keep last, obviously */
 	NUM_IEEE80211_HW_FLAGS
@@ -3814,6 +3839,8 @@ enum ieee80211_reconfig_type {
  * @set_tid_config: Apply TID specific configurations. This callback may sleep.
  * @reset_tid_config: Reset TID specific configuration for the peer.
  *	This callback may sleep.
+ * @update_vif_config: Update virtual interface offload flags
+ *	This callback may sleep.
  */
 struct ieee80211_ops {
 	void (*tx)(struct ieee80211_hw *hw,
@@ -4125,6 +4152,8 @@ struct ieee80211_ops {
 	int (*reset_tid_config)(struct ieee80211_hw *hw,
 				struct ieee80211_vif *vif,
 				struct ieee80211_sta *sta, u8 tids);
+	void (*update_vif_offload)(struct ieee80211_hw *hw,
+				   struct ieee80211_vif *vif);
 };
 
 /**