Commit a80509c7 authored by Mark A. Greer's avatar Mark A. Greer Committed by Samuel Ortiz
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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: default avatarThierry Escande <thierry.escande@linux.intel.com>
Tested-by: default avatarThierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: default avatarMark A. Greer <mgreer@animalcreek.com>
Signed-off-by: default avatarSamuel Ortiz <sameo@linux.intel.com>
parent c12715ab

include/net/nfc/digital.h

+2 −0
Original line number Diff line number Diff line
@@ -233,6 +233,8 @@ struct nfc_digital_dev { 
	struct sk_buff *chaining_skb;

	struct digital_data_exch *data_exch;



	int nack_count;



	u16 target_fsc;



	int (*skb_check_crc)(struct sk_buff *skb);

net/nfc/digital_dep.c

+64 −5
Original line number Diff line number Diff line
@@ -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)

{
@@ -575,13 +609,17 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg, 
	if (IS_ERR(resp)) {

		rc = PTR_ERR(resp);

		resp = NULL;

		goto exit;

	}



	rc = ddev->skb_check_crc(resp);

	if (rc) {

		PROTOCOL_ERR("14.4.1.6");

		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);
@@ -590,6 +628,25 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg, 
		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;

	}



	ddev->nack_count = 0;



	if (resp->len > ddev->local_payload_max) {

		rc = -EMSGSIZE;

		goto exit;
@@ -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);

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