ieee802154: cc2520: Check CRC & add promiscuous

This patch adds checking the "CRC_OK" bit at the end of packets coming
from the CC2520 radio. It also adds support for putting the radio in
promiscuous mode (in which packets are not dropped if the CRC fails).
In promiscuous mode the AUTOCRC flag is cleared so that the driver can
pass the received CRC to the monitors.

The radio now defaults to frame filtering (checking that the destination
and PANID in the incoming packet matches the local node). This matches
the other 15.4 radios and is what a user would expect to be the default.

Other changes:

1. Adds LQI calculation
2. Makes #defines for relevant bit fields in CC2520 registers

Signed-off-by: Brad Campbell <bradjc5@gmail.com>
Acked-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/net/ieee802154/cc2520.c

@@ -21,6 +21,8 @@
 #include <linux/skbuff.h>
 #include <linux/of_gpio.h>
 #include <linux/ieee802154.h>
+#include <linux/crc-ccitt.h>
+#include <asm/unaligned.h>
 
 #include <net/mac802154.h>
 #include <net/cfg802154.h>
@@ -189,6 +191,18 @@
 #define	CC2520_RXFIFOCNT		0x3E
 #define	CC2520_TXFIFOCNT		0x3F
 
+/* CC2520_FRMFILT0 */
+#define FRMFILT0_FRAME_FILTER_EN	BIT(0)
+#define FRMFILT0_PAN_COORDINATOR	BIT(1)
+
+/* CC2520_FRMCTRL0 */
+#define FRMCTRL0_AUTOACK		BIT(5)
+#define FRMCTRL0_AUTOCRC		BIT(6)
+
+/* CC2520_FRMCTRL1 */
+#define FRMCTRL1_SET_RXENMASK_ON_TX	BIT(0)
+#define FRMCTRL1_IGNORE_TX_UNDERF	BIT(1)
+
 /* Driver private information */
 struct cc2520_private {
 	struct spi_device *spi;		/* SPI device structure */
@@ -201,6 +215,7 @@ struct cc2520_private {
 	struct work_struct fifop_irqwork;/* Workqueue for FIFOP */
 	spinlock_t lock;		/* Lock for is_tx*/
 	struct completion tx_complete;	/* Work completion for Tx */
+	bool promiscuous;               /* Flag for promiscuous mode */
 };
 
 /* Generic Functions */
@@ -367,14 +382,14 @@ cc2520_read_register(struct cc2520_private *priv, u8 reg, u8 *data)
 }
 
 static int
-cc2520_write_txfifo(struct cc2520_private *priv, u8 *data, u8 len)
+cc2520_write_txfifo(struct cc2520_private *priv, u8 pkt_len, u8 *data, u8 len)
 {
 	int status;
 
 	/* length byte must include FCS even
 	 * if it is calculated in the hardware
 	 */
-	int len_byte = len + 2;
+	int len_byte = pkt_len;
 
 	struct spi_message msg;
 
@@ -414,7 +429,7 @@ cc2520_write_txfifo(struct cc2520_private *priv, u8 *data, u8 len)
 }
 
 static int
-cc2520_read_rxfifo(struct cc2520_private *priv, u8 *data, u8 len, u8 *lqi)
+cc2520_read_rxfifo(struct cc2520_private *priv, u8 *data, u8 len)
 {
 	int status;
 	struct spi_message msg;
@@ -470,12 +485,25 @@ cc2520_tx(struct ieee802154_hw *hw, struct sk_buff *skb)
 	unsigned long flags;
 	int rc;
 	u8 status = 0;
+	u8 pkt_len;
+
+	/* In promiscuous mode we disable AUTOCRC so we can get the raw CRC
+	 * values on RX. This means we need to manually add the CRC on TX.
+	 */
+	if (priv->promiscuous) {
+		u16 crc = crc_ccitt(0, skb->data, skb->len);
+
+		put_unaligned_le16(crc, skb_put(skb, 2));
+		pkt_len = skb->len;
+	} else {
+		pkt_len = skb->len + 2;
+	}
 
 	rc = cc2520_cmd_strobe(priv, CC2520_CMD_SFLUSHTX);
 	if (rc)
 		goto err_tx;
 
-	rc = cc2520_write_txfifo(priv, skb->data, skb->len);
+	rc = cc2520_write_txfifo(priv, pkt_len, skb->data, skb->len);
 	if (rc)
 		goto err_tx;
 
@@ -518,22 +546,62 @@ static int cc2520_rx(struct cc2520_private *priv)
 	u8 len = 0, lqi = 0, bytes = 1;
 	struct sk_buff *skb;
 
-	cc2520_read_rxfifo(priv, &len, bytes, &lqi);
+	/* Read single length byte from the radio. */
+	cc2520_read_rxfifo(priv, &len, bytes);
 
-	if (len < 2 || len > IEEE802154_MTU)
-		return -EINVAL;
+	if (!ieee802154_is_valid_psdu_len(len)) {
+		/* Corrupted frame received, clear frame buffer by
+		 * reading entire buffer.
+		 */
+		dev_dbg(&priv->spi->dev, "corrupted frame received\n");
+		len = IEEE802154_MTU;
+	}
 
 	skb = dev_alloc_skb(len);
 	if (!skb)
 		return -ENOMEM;
 
-	if (cc2520_read_rxfifo(priv, skb_put(skb, len), len, &lqi)) {
+	if (cc2520_read_rxfifo(priv, skb_put(skb, len), len)) {
 		dev_dbg(&priv->spi->dev, "frame reception failed\n");
 		kfree_skb(skb);
 		return -EINVAL;
 	}
 
-	skb_trim(skb, skb->len - 2);
+	/* In promiscuous mode, we configure the radio to include the
+	 * CRC (AUTOCRC==0) and we pass on the packet unconditionally. If not
+	 * in promiscuous mode, we check the CRC here, but leave the
+	 * RSSI/LQI/CRC_OK bytes as they will get removed in the mac layer.
+	 */
+	if (!priv->promiscuous) {
+		bool crc_ok;
+
+		/* Check if the CRC is valid. With AUTOCRC set, the most
+		 * significant bit of the last byte returned from the CC2520
+		 * is CRC_OK flag. See section 20.3.4 of the datasheet.
+		 */
+		crc_ok = skb->data[len - 1] & BIT(7);
+
+		/* If we failed CRC drop the packet in the driver layer. */
+		if (!crc_ok) {
+			dev_dbg(&priv->spi->dev, "CRC check failed\n");
+			kfree_skb(skb);
+			return -EINVAL;
+		}
+
+		/* To calculate LQI, the lower 7 bits of the last byte (the
+		 * correlation value provided by the radio) must be scaled to
+		 * the range 0-255. According to section 20.6, the correlation
+		 * value ranges from 50-110. Ideally this would be calibrated
+		 * per hardware design, but we use roughly the datasheet values
+		 * to get close enough while avoiding floating point.
+		 */
+		lqi = skb->data[len - 1] & 0x7f;
+		if (lqi < 50)
+			lqi = 50;
+		else if (lqi > 113)
+			lqi = 113;
+		lqi = (lqi - 50) * 4;
+	}
 
 	ieee802154_rx_irqsafe(priv->hw, skb, lqi);
 
@@ -619,14 +687,19 @@ cc2520_filter(struct ieee802154_hw *hw,
 	}
 
 	if (changed & IEEE802154_AFILT_PANC_CHANGED) {
+		u8 frmfilt0;
+
 		dev_vdbg(&priv->spi->dev,
 			 "cc2520_filter called for panc change\n");
+
+		cc2520_read_register(priv, CC2520_FRMFILT0, &frmfilt0);
+
 		if (filt->pan_coord)
-			ret = cc2520_write_register(priv, CC2520_FRMFILT0,
-						    0x02);
+			frmfilt0 |= FRMFILT0_PAN_COORDINATOR;
 		else
-			ret = cc2520_write_register(priv, CC2520_FRMFILT0,
-						    0x00);
+			frmfilt0 &= ~FRMFILT0_PAN_COORDINATOR;
+
+		ret = cc2520_write_register(priv, CC2520_FRMFILT0, frmfilt0);
 	}
 
 	return ret;
@@ -723,6 +796,30 @@ cc2520_set_txpower(struct ieee802154_hw *hw, s32 mbm)
 	return cc2520_cc2591_set_tx_power(priv, mbm);
 }
 
+static int
+cc2520_set_promiscuous_mode(struct ieee802154_hw *hw, bool on)
+{
+	struct cc2520_private *priv = hw->priv;
+	u8 frmfilt0;
+
+	dev_dbg(&priv->spi->dev, "%s : mode %d\n", __func__, on);
+
+	priv->promiscuous = on;
+
+	cc2520_read_register(priv, CC2520_FRMFILT0, &frmfilt0);
+
+	if (on) {
+		/* Disable automatic ACK, automatic CRC, and frame filtering. */
+		cc2520_write_register(priv, CC2520_FRMCTRL0, 0);
+		frmfilt0 &= ~FRMFILT0_FRAME_FILTER_EN;
+	} else {
+		cc2520_write_register(priv, CC2520_FRMCTRL0, FRMCTRL0_AUTOACK |
+							     FRMCTRL0_AUTOCRC);
+		frmfilt0 |= FRMFILT0_FRAME_FILTER_EN;
+	}
+	return cc2520_write_register(priv, CC2520_FRMFILT0, frmfilt0);
+}
+
 static const struct ieee802154_ops cc2520_ops = {
 	.owner = THIS_MODULE,
 	.start = cc2520_start,
@@ -732,6 +829,7 @@ static const struct ieee802154_ops cc2520_ops = {
 	.set_channel = cc2520_set_channel,
 	.set_hw_addr_filt = cc2520_filter,
 	.set_txpower = cc2520_set_txpower,
+	.set_promiscuous_mode = cc2520_set_promiscuous_mode,
 };
 
 static int cc2520_register(struct cc2520_private *priv)
@@ -749,7 +847,8 @@ static int cc2520_register(struct cc2520_private *priv)
 
 	/* We do support only 2.4 Ghz */
 	priv->hw->phy->supported.channels[0] = 0x7FFF800;
-	priv->hw->flags = IEEE802154_HW_OMIT_CKSUM | IEEE802154_HW_AFILT;
+	priv->hw->flags = IEEE802154_HW_TX_OMIT_CKSUM | IEEE802154_HW_AFILT |
+			  IEEE802154_HW_PROMISCUOUS;
 
 	priv->hw->phy->flags = WPAN_PHY_FLAG_TXPOWER;
 
@@ -919,6 +1018,11 @@ static int cc2520_hw_init(struct cc2520_private *priv)
 	}
 
 	/* Registers default value: section 28.1 in Datasheet */
+
+	/* Set the CCA threshold to -50 dBm. This seems to have been copied
+	 * from the TinyOS CC2520 driver and is much higher than the -84 dBm
+	 * threshold suggested in the datasheet.
+	 */
 	ret = cc2520_write_register(priv, CC2520_CCACTRL0, 0x1A);
 	if (ret)
 		goto err_ret;
@@ -955,15 +1059,10 @@ static int cc2520_hw_init(struct cc2520_private *priv)
 	if (ret)
 		goto err_ret;
 
-	ret = cc2520_write_register(priv, CC2520_FRMCTRL0, 0x60);
-	if (ret)
-		goto err_ret;
-
-	ret = cc2520_write_register(priv, CC2520_FRMCTRL1, 0x03);
-	if (ret)
-		goto err_ret;
-
-	ret = cc2520_write_register(priv, CC2520_FRMFILT0, 0x00);
+	/* Configure registers correctly for this driver. */
+	ret = cc2520_write_register(priv, CC2520_FRMCTRL1,
+				    FRMCTRL1_SET_RXENMASK_ON_TX |
+				    FRMCTRL1_IGNORE_TX_UNDERF);
 	if (ret)
 		goto err_ret;