drivers: bluetooth: silabs: Potentially discard unimportant HCI events

Certain HCI events, like advertising reports, are of less importance than
others. This takes the discardable buffer pool into use for such events.
When the system is flooded with advertising reports, discarding some of
them ensures that the system can still handle other events.

Signed-off-by: Kalle Kietäväinen <kalle.kietavainen@silabs.com>

Author: kietavainen

drivers/bluetooth/hci/hci_silabs_efr32.c

@@ -71,6 +71,82 @@ void rail_isr_installer(void)
 	IRQ_CONNECT(AGC_IRQn, 0, AGC_IRQHandler, NULL, 0);
 }
 
+static bool slz_is_evt_discardable(const struct bt_hci_evt_hdr *hdr, const uint8_t *params,
+				   int16_t params_len)
+{
+	switch (hdr->evt) {
+	case BT_HCI_EVT_LE_META_EVENT: {
+		struct bt_hci_evt_le_meta_event *meta_evt = (void *)params;
+
+		if (params_len < sizeof(*meta_evt)) {
+			return false;
+		}
+		params += sizeof(*meta_evt);
+		params_len -= sizeof(*meta_evt);
+
+		switch (meta_evt->subevent) {
+		case BT_HCI_EVT_LE_ADVERTISING_REPORT:
+			return true;
+		case BT_HCI_EVT_LE_EXT_ADVERTISING_REPORT: {
+			struct bt_hci_evt_le_ext_advertising_report *evt = (void *)params;
+
+			if (!IS_ENABLED(CONFIG_BT_EXT_ADV)) {
+				return false;
+			}
+
+			if (params_len < sizeof(*evt) + sizeof(*evt->adv_info)) {
+				return false;
+			}
+
+			/* Never discard if the event could be part of a multi-part report event,
+			 * because the missing part could confuse the BT host.
+			 */
+			return (evt->num_reports == 1) &&
+			       ((evt->adv_info[0].evt_type & BT_HCI_LE_ADV_EVT_TYPE_LEGACY) != 0);
+		}
+		default:
+			return false;
+		}
+	}
+	default:
+		return false;
+	}
+}
+
+static struct net_buf *slz_bt_recv_evt(const uint8_t *data, const int16_t len)
+{
+	struct net_buf *buf;
+	bool discardable;
+	const struct bt_hci_evt_hdr *hdr = (void *)data;
+	const uint8_t *params = &data[sizeof(*hdr)];
+	const int16_t params_len = len - sizeof(*hdr);
+
+	if (len < sizeof(*hdr)) {
+		LOG_ERR("Event header is missing");
+		return NULL;
+	}
+
+	discardable = slz_is_evt_discardable(hdr, params, params_len);
+	buf = bt_buf_get_evt(hdr->evt, discardable, discardable ? K_NO_WAIT : K_FOREVER);
+	if (!buf) {
+		LOG_DBG("Discardable buffer pool full, ignoring event");
+		return buf;
+	}
+
+	net_buf_add_mem(buf, data, len);
+
+	return buf;
+}
+
+static struct net_buf *slz_bt_recv_acl(const uint8_t *data, const int16_t len)
+{
+	struct net_buf *buf = bt_buf_get_rx(BT_BUF_ACL_IN, K_FOREVER);
+
+	net_buf_add_mem(buf, data, len);
+
+	return buf;
+}
+
 /**
  * @brief Transmit HCI message using the currently used transport layer.
  * The HCI calls this function to transmit a full HCI message.
@@ -81,30 +157,35 @@ void rail_isr_installer(void)
 uint32_t hci_common_transport_transmit(uint8_t *data, int16_t len)
 {
 	struct net_buf *buf;
-	uint8_t packet_type = data[0];
-	uint8_t event_code;
+	uint8_t packet_type;
 
 	LOG_HEXDUMP_DBG(data, len, "host packet data:");
 
+	if (len < 1) {
+		LOG_ERR("HCI packet type is missing");
+		return -EINVAL;
+	}
+
+	packet_type = data[0];
 	/* drop packet type from the frame buffer - it is no longer needed */
-	data = &data[1];
+	data += 1;
 	len -= 1;
 
 	switch (packet_type) {
 	case BT_HCI_H4_EVT:
-		event_code = data[0];
-		buf = bt_buf_get_evt(event_code, false, K_FOREVER);
+		buf = slz_bt_recv_evt(data, len);
 		break;
 	case BT_HCI_H4_ACL:
-		buf = bt_buf_get_rx(BT_BUF_ACL_IN, K_FOREVER);
+		buf = slz_bt_recv_acl(data, len);
 		break;
 	default:
 		LOG_ERR("Unknown HCI type: %d", packet_type);
 		return -EINVAL;
 	}
 
-	net_buf_add_mem(buf, data, len);
-	k_fifo_put(&slz_rx_fifo, buf);
+	if (buf) {
+		k_fifo_put(&slz_rx_fifo, buf);
+	}
 
 	sl_btctrl_hci_transmit_complete(0);