NFC: digital: Fix ACK & NACK PDUs handling in target mode

When the target receives a NACK PDU, it re-sends the last sent PDU.

ACK PDUs are received by the target as a reply from the initiator to
chained I-PDUs. There are 3 cases to handle:
- If the target has previously received 1 or more ATN PDUs and the PNI
  in the ACK PDU is equal to the target PNI - 1, then it means that the
  initiator did not received the last issued PDU from the target. In
  this case it re-sends this PDU.
- If the target has received 1 or more ATN PDUs but the ACK PNI is not
  the target PNI - 1, then this means that this ACK is the reply of the
  previous chained I-PDU sent by the target. The target did not received
  it on the first attempt and it is being re-sent by the initiator. The
  process continues as usual.
- No ATN PDU received before this ACK PDU. This is the reply of a
  chained I-PDU. The target keeps on processing its chained I-PDU.

The code has been refactored to avoid too many indentation levels.

Also, ACK and NACK PDUs were not freed. This is now fixed.

Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

1 files changed, 43 insertions, 28 deletions

diff --git a/net/nfc/digital_dep.c b/net/nfc/digital_dep.c
index 1778c23751d4..e0268777ab18 100644
--- a/net/nfc/digital_dep.c
+++ b/net/nfc/digital_dep.c
@@ -1141,49 +1141,64 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
                 rc = 0;
                 break;
         case DIGITAL_NFC_DEP_PFB_ACK_NACK_PDU:
-                if (!DIGITAL_NFC_DEP_NACK_BIT_SET(pfb)) { /* ACK */
-                        if ((ddev->atn_count &&
-                             (DIGITAL_NFC_DEP_PFB_PNI(pfb - 1) !=
-                                                ddev->curr_nfc_dep_pni)) ||
-                            (DIGITAL_NFC_DEP_PFB_PNI(pfb) !=
-                                                ddev->curr_nfc_dep_pni) ||
-                            !ddev->chaining_skb || !ddev->saved_skb) {
+                if (DIGITAL_NFC_DEP_NACK_BIT_SET(pfb)) { /* NACK */
+                        if (DIGITAL_NFC_DEP_PFB_PNI(pfb + 1) !=
+                                                ddev->curr_nfc_dep_pni) {
                                 rc = -EIO;
                                 goto exit;
                         }
 
-                        if (ddev->atn_count) {
-                                ddev->atn_count = 0;
+                        ddev->atn_count = 0;
+
+                        rc = digital_tg_send_saved_skb(ddev);
+                        if (rc)
+                                goto exit;
+
+                        goto free_resp;
+                }
+
+                /* ACK */
+                if (ddev->atn_count) {
+                        /* The target has previously recevied one or more ATN
+                         * PDUs.
+                         */
+                        ddev->atn_count = 0;
 
+                        /* If the ACK PNI is equal to the target PNI - 1 means
+                         * that the initiator did not receive the previous PDU
+                         * sent by the target so re-send it.
+                         */
+                        if (DIGITAL_NFC_DEP_PFB_PNI(pfb + 1) ==
+                                                ddev->curr_nfc_dep_pni) {
                                 rc = digital_tg_send_saved_skb(ddev);
                                 if (rc)
                                         goto exit;
 
-                                return;
+                                goto free_resp;
                         }
 
-                        kfree_skb(ddev->saved_skb);
-                        ddev->saved_skb = NULL;
+                        /* Otherwise, the target did not receive the previous
+                         * ACK PDU from the initiator. Fallback to normal
+                         * processing of chained PDU then.
+                         */
+                }
 
-                        rc = digital_tg_send_dep_res(ddev, ddev->chaining_skb);
-                        if (rc)
-                                goto exit;
-                } else { /* NACK */
-                        if ((DIGITAL_NFC_DEP_PFB_PNI(pfb + 1) !=
-                                                ddev->curr_nfc_dep_pni) ||
-                            !ddev->saved_skb) {
-                                rc = -EIO;
-                                goto exit;
-                        }
+                /* Keep on sending chained PDU */
+                if (!ddev->chaining_skb ||
+                    DIGITAL_NFC_DEP_PFB_PNI(pfb) !=
+                                        ddev->curr_nfc_dep_pni) {
+                        rc = -EIO;
+                        goto exit;
+                }
 
-                        ddev->atn_count = 0;
+                kfree_skb(ddev->saved_skb);
+                ddev->saved_skb = NULL;
 
-                        rc = digital_tg_send_saved_skb(ddev);
-                        if (rc)
-                                goto exit;
-                }
+                rc = digital_tg_send_dep_res(ddev, ddev->chaining_skb);
+                if (rc)
+                        goto exit;
 
-                return;
+                goto free_resp;
         case DIGITAL_NFC_DEP_PFB_SUPERVISOR_PDU:
                 if (DIGITAL_NFC_DEP_PFB_IS_TIMEOUT(pfb)) {
                         rc = -EINVAL;