NFC: digital: Add NFC-DEP Receive Chaining Support

When the peer in an NFC-DEP exchange has a
packet to send that is larger than the local
maximum payload, it sets the 'MI' bit in the
'I' PDU.  This indicates that NFC-DEP chaining
is to occur.

When such a PDU is received, the local side
responds with an 'ACK' PDU and this continues
until the peer sends an 'I' PDU with the 'MI'
bit cleared.  This indicates that the chaining
sequence is complete and the entire packet has
been transferred.

Receiving chained PDUs is currently not supported
by the digital layer so add that support.  When a
chaining sequence is initiated by the peer, the
digital layer will allocate an skb large enough
to hold 8 maximum sized frame payloads.  The maximum
payload can range from 64 to 254 bytes so 8 * 254 =
2032 seems like a reasonable compromise between
potentially wasting memory and constantly reallocating
new, larger skbs.

Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

net/nfc/digital_dep.c

@@ -109,6 +109,8 @@ struct digital_dep_req_res {
 
 static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
 				    struct sk_buff *resp);
+static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
+				    struct sk_buff *resp);
 
 static const u8 digital_payload_bits_map[4] = {
 	[0] = 64,
@@ -201,6 +203,72 @@ digital_send_dep_data_prep(struct nfc_digital_dev *ddev, struct sk_buff *skb,
 	return new_skb;
 }
 
+static struct sk_buff *
+digital_recv_dep_data_gather(struct nfc_digital_dev *ddev, u8 pfb,
+			     struct sk_buff *resp,
+			     int (*send_ack)(struct nfc_digital_dev *ddev,
+					     struct digital_data_exch
+							     *data_exch),
+			     struct digital_data_exch *data_exch)
+{
+	struct sk_buff *new_skb;
+	int rc;
+
+	if (DIGITAL_NFC_DEP_MI_BIT_SET(pfb) && (!ddev->chaining_skb)) {
+		ddev->chaining_skb =
+			nfc_alloc_recv_skb(8 * ddev->local_payload_max,
+					   GFP_KERNEL);
+		if (!ddev->chaining_skb) {
+			rc = -ENOMEM;
+			goto error;
+		}
+	}
+
+	if (ddev->chaining_skb) {
+		if (resp->len > skb_tailroom(ddev->chaining_skb)) {
+			new_skb = skb_copy_expand(ddev->chaining_skb,
+						  skb_headroom(
+							  ddev->chaining_skb),
+						  8 * ddev->local_payload_max,
+						  GFP_KERNEL);
+			if (!new_skb) {
+				rc = -ENOMEM;
+				goto error;
+			}
+
+			kfree_skb(ddev->chaining_skb);
+			ddev->chaining_skb = new_skb;
+		}
+
+		memcpy(skb_put(ddev->chaining_skb, resp->len), resp->data,
+		       resp->len);
+
+		kfree_skb(resp);
+		resp = NULL;
+
+		if (DIGITAL_NFC_DEP_MI_BIT_SET(pfb)) {
+			rc = send_ack(ddev, data_exch);
+			if (rc)
+				goto error;
+
+			return NULL;
+		}
+
+		resp = ddev->chaining_skb;
+		ddev->chaining_skb = NULL;
+	}
+
+	return resp;
+
+error:
+	kfree_skb(resp);
+
+	kfree_skb(ddev->chaining_skb);
+	ddev->chaining_skb = NULL;
+
+	return ERR_PTR(rc);
+}
+
 static void digital_in_recv_psl_res(struct nfc_digital_dev *ddev, void *arg,
 				    struct sk_buff *resp)
 {
@@ -429,6 +497,38 @@ int digital_in_send_atr_req(struct nfc_digital_dev *ddev,
 	return rc;
 }
 
+static int digital_in_send_ack(struct nfc_digital_dev *ddev,
+			       struct digital_data_exch *data_exch)
+{
+	struct digital_dep_req_res *dep_req;
+	struct sk_buff *skb;
+	int rc;
+
+	skb = digital_skb_alloc(ddev, 1);
+	if (!skb)
+		return -ENOMEM;
+
+	skb_push(skb, sizeof(struct digital_dep_req_res));
+
+	dep_req = (struct digital_dep_req_res *)skb->data;
+
+	dep_req->dir = DIGITAL_NFC_DEP_FRAME_DIR_OUT;
+	dep_req->cmd = DIGITAL_CMD_DEP_REQ;
+	dep_req->pfb = DIGITAL_NFC_DEP_PFB_ACK_NACK_PDU |
+		       ddev->curr_nfc_dep_pni;
+
+	digital_skb_push_dep_sod(ddev, skb);
+
+	ddev->skb_add_crc(skb);
+
+	rc = digital_in_send_cmd(ddev, skb, 1500, digital_in_recv_dep_res,
+				 data_exch);
+	if (rc)
+		kfree_skb(skb);
+
+	return rc;
+}
+
 static int digital_in_send_rtox(struct nfc_digital_dev *ddev,
 				struct digital_data_exch *data_exch, u8 rtox)
 {
@@ -534,6 +634,23 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
 
 		ddev->curr_nfc_dep_pni =
 			DIGITAL_NFC_DEP_PFB_PNI(ddev->curr_nfc_dep_pni + 1);
+
+		resp = digital_recv_dep_data_gather(ddev, pfb, resp,
+						    digital_in_send_ack,
+						    data_exch);
+		if (IS_ERR(resp)) {
+			rc = PTR_ERR(resp);
+			resp = NULL;
+			goto error;
+		}
+
+		/* If resp is NULL then we're still chaining so return and
+		 * wait for the next part of the PDU.  Else, the PDU is
+		 * complete so pass it up.
+		 */
+		if (!resp)
+			return;
+
 		rc = 0;
 		break;
 
@@ -575,12 +692,6 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
 		return;
 	}
 
-	if (DIGITAL_NFC_DEP_MI_BIT_SET(pfb)) {
-		pr_err("MI bit set. Chained PDU not supported\n");
-		rc = -EIO;
-		goto error;
-	}
-
 exit:
 	data_exch->cb(data_exch->cb_context, resp, rc);
 
@@ -660,6 +771,48 @@ static void digital_tg_set_rf_tech(struct nfc_digital_dev *ddev, u8 rf_tech)
 	}
 }
 
+static int digital_tg_send_ack(struct nfc_digital_dev *ddev,
+			       struct digital_data_exch *data_exch)
+{
+	struct digital_dep_req_res *dep_res;
+	struct sk_buff *skb;
+	int rc;
+
+	skb = digital_skb_alloc(ddev, 1);
+	if (!skb)
+		return -ENOMEM;
+
+	skb_push(skb, sizeof(struct digital_dep_req_res));
+
+	dep_res = (struct digital_dep_req_res *)skb->data;
+
+	dep_res->dir = DIGITAL_NFC_DEP_FRAME_DIR_IN;
+	dep_res->cmd = DIGITAL_CMD_DEP_RES;
+	dep_res->pfb = DIGITAL_NFC_DEP_PFB_ACK_NACK_PDU |
+		       ddev->curr_nfc_dep_pni;
+
+	if (ddev->did) {
+		dep_res->pfb |= DIGITAL_NFC_DEP_PFB_DID_BIT;
+
+		memcpy(skb_put(skb, sizeof(ddev->did)), &ddev->did,
+		       sizeof(ddev->did));
+	}
+
+	ddev->curr_nfc_dep_pni =
+		DIGITAL_NFC_DEP_PFB_PNI(ddev->curr_nfc_dep_pni + 1);
+
+	digital_skb_push_dep_sod(ddev, skb);
+
+	ddev->skb_add_crc(skb);
+
+	rc = digital_tg_send_cmd(ddev, skb, 1500, digital_tg_recv_dep_req,
+				 data_exch);
+	if (rc)
+		kfree_skb(skb);
+
+	return rc;
+}
+
 static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
 				    struct sk_buff *resp)
 {
@@ -736,6 +889,21 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
 			goto exit;
 		}
 
+		resp = digital_recv_dep_data_gather(ddev, pfb, resp,
+						    digital_tg_send_ack, NULL);
+		if (IS_ERR(resp)) {
+			rc = PTR_ERR(resp);
+			resp = NULL;
+			goto exit;
+		}
+
+		/* If resp is NULL then we're still chaining so return and
+		 * wait for the next part of the PDU.  Else, the PDU is
+		 * complete so pass it up.
+		 */
+		if (!resp)
+			return;
+
 		rc = 0;
 		break;
 	case DIGITAL_NFC_DEP_PFB_ACK_NACK_PDU: