NFC: digital: Add NFC-DEP Initiator-side NACK Support

When an NFC-DEP Initiator receives a frame with
an incorrect CRC or with a parity error, and the
frame is at least 4 bytes long, its supposed to
send a NACK to the Target.  The Initiator can
send up to 'N(retry,nack)' consecutive NACKs
where 2 <= 'N(retry,nack)' <= 5.  When the limit
is exceeded, a PROTOCOL EXCEPTION is raised.
Any other type of transmission error is to be
ignored and the Initiator should continue
waiting for a new frame.  This is described
in section 14.12.5.4 of the NFC Digital Protocol
Spec.

The digital layer's NFC-DEP code doesn't implement
any of this so add it.  This support diverges from
the spec in two significant ways:

a) NACKs will be sent for ANY error reported by the
   driver except a timeout.  This is done because
   there is currently no way for the digital layer
   to distinguish a CRC or parity error from any
   other type of error reported by the driver.

b) All other errors will cause a PROTOCOL EXCEPTION
   even frames with CRC errors that are less than 4
   bytes.

The value chosen for 'N(retry,nack)' is 2.

Targets do not send NACK PDUs.

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>

1 files changed, 64 insertions, 5 deletions

diff --git a/net/nfc/digital_dep.c b/net/nfc/digital_dep.c
index 35a9edf0e360..9840e858ec5b 100644
--- a/net/nfc/digital_dep.c
+++ b/net/nfc/digital_dep.c
@@ -17,6 +17,8 @@
 
 #include "digital.h"
 
+#define DIGITAL_NFC_DEP_N_RETRY_NACK    2
+
 #define DIGITAL_NFC_DEP_FRAME_DIR_OUT 0xD4
 #define DIGITAL_NFC_DEP_FRAME_DIR_IN  0xD5
 
@@ -529,6 +531,38 @@ static int digital_in_send_ack(struct nfc_digital_dev *ddev,
         return rc;
 }
 
+static int digital_in_send_nack(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 |
+                       DIGITAL_NFC_DEP_PFB_NACK_BIT | 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)
 {
@@ -575,20 +609,43 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
         if (IS_ERR(resp)) {
                 rc = PTR_ERR(resp);
                 resp = NULL;
+
+                if ((rc != -ETIMEDOUT) &&
+                    (ddev->nack_count++ < DIGITAL_NFC_DEP_N_RETRY_NACK)) {
+                        rc = digital_in_send_nack(ddev, data_exch);
+                        if (rc)
+                                goto error;
+
+                        return;
+                }
+
+                goto exit;
+        }
+
+        rc = digital_skb_pull_dep_sod(ddev, resp);
+        if (rc) {
+                PROTOCOL_ERR("14.4.1.2");
                 goto exit;
         }
 
         rc = ddev->skb_check_crc(resp);
         if (rc) {
+                if ((resp->len >= 4) &&
+                    (ddev->nack_count++ < DIGITAL_NFC_DEP_N_RETRY_NACK)) {
+                        rc = digital_in_send_nack(ddev, data_exch);
+                        if (rc)
+                                goto error;
+
+                        kfree_skb(resp);
+
+                        return;
+                }
+
                 PROTOCOL_ERR("14.4.1.6");
                 goto error;
         }
 
-        rc = digital_skb_pull_dep_sod(ddev, resp);
-        if (rc) {
-                PROTOCOL_ERR("14.4.1.2");
-                goto exit;
-        }
+        ddev->nack_count = 0;
 
         if (resp->len > ddev->local_payload_max) {
                 rc = -EMSGSIZE;
@@ -721,6 +778,8 @@ int digital_in_send_dep_req(struct nfc_digital_dev *ddev,
         dep_req->cmd = DIGITAL_CMD_DEP_REQ;
         dep_req->pfb = ddev->curr_nfc_dep_pni;
 
+        ddev->nack_count = 0;
+
         chaining_skb = ddev->chaining_skb;
 
         tmp_skb = digital_send_dep_data_prep(ddev, skb, dep_req, data_exch);