drivers/uwb/wlp/txrx.c - kernel/msm-4.9 - Gitiles

 /*
  * WiMedia Logical Link Control Protocol (WLP)
  * Message exchange infrastructure
  *
  * Copyright (C) 2007 Intel Corporation
  * Reinette Chatre <reinette.chatre@intel.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License version
  * 2 as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  * 02110-1301, USA.
  *
  *
  * FIXME: Docs
  *
  */

 #include <linux/etherdevice.h>
 #include <linux/wlp.h>

 #include "wlp-internal.h"

 /*
  * Direct incoming association msg to correct parsing routine
  *
  * We only expect D1, E1, C1, C3 messages as new. All other incoming
  * association messages should form part of an established session that is
  * handled elsewhere.
  * The handling of these messages often require calling sleeping functions
  * - this cannot be done in interrupt context. We use the kernel's
  * workqueue to handle these messages.
  */
 static
 void wlp_direct_assoc_frame(struct wlp *wlp, struct sk_buff *skb,
 			   struct uwb_dev_addr *src)
 {
 	struct device *dev = &wlp->rc->uwb_dev.dev;
 	struct wlp_frame_assoc *assoc = (void *) skb->data;
 	struct wlp_assoc_frame_ctx *frame_ctx;

 	frame_ctx = kmalloc(sizeof(*frame_ctx), GFP_ATOMIC);
 	if (frame_ctx == NULL) {
 		dev_err(dev, "WLP: Unable to allocate memory for association "
 			"frame handling.\n");
 		kfree_skb(skb);
 		return;
 	}
 	frame_ctx->wlp = wlp;
 	frame_ctx->skb = skb;
 	frame_ctx->src = *src;
 	switch (assoc->type) {
 	case WLP_ASSOC_D1:
 		INIT_WORK(&frame_ctx->ws, wlp_handle_d1_frame);
 		schedule_work(&frame_ctx->ws);
 		break;
 	case WLP_ASSOC_E1:
 		kfree_skb(skb); /* Temporary until we handle it */
 		kfree(frame_ctx); /* Temporary until we handle it */
 		break;
 	case WLP_ASSOC_C1:
 		INIT_WORK(&frame_ctx->ws, wlp_handle_c1_frame);
 		schedule_work(&frame_ctx->ws);
 		break;
 	case WLP_ASSOC_C3:
 		INIT_WORK(&frame_ctx->ws, wlp_handle_c3_frame);
 		schedule_work(&frame_ctx->ws);
 		break;
 	default:
 		dev_err(dev, "Received unexpected association frame. "
 			"Type = %d \n", assoc->type);
 		kfree_skb(skb);
 		kfree(frame_ctx);
 		break;
 	}
 }

 /*
  * Process incoming association frame
  *
  * Although it could be possible to deal with some incoming association
  * messages without creating a new session we are keeping things simple. We
  * do not accept new association messages if there is a session in progress
  * and the messages do not belong to that session.
  *
  * If an association message arrives that causes the creation of a session
  * (WLP_ASSOC_E1) while we are in the process of creating a session then we
  * rely on the neighbor mutex to protect the data. That is, the new session
  * will not be started until the previous is completed.
  */
 static
 void wlp_receive_assoc_frame(struct wlp *wlp, struct sk_buff *skb,
 			     struct uwb_dev_addr *src)
 {
 	struct device *dev = &wlp->rc->uwb_dev.dev;
 	struct wlp_frame_assoc *assoc = (void *) skb->data;
 	struct wlp_session *session = wlp->session;
 	u8 version;

 	if (wlp_get_version(wlp, &assoc->version, &version,
 			    sizeof(assoc->version)) < 0)
 		goto error;
 	if (version != WLP_VERSION) {
 		dev_err(dev, "Unsupported WLP version in association "
 			"message.\n");
 		goto error;
 	}
 	if (session != NULL) {
 		/* Function that created this session is still holding the
 		 * &wlp->mutex to protect this session. */
 		if (assoc->type == session->exp_message ||
 		    assoc->type == WLP_ASSOC_F0) {
 			if (!memcmp(&session->neighbor_addr, src,
 				   sizeof(*src))) {
 				session->data = skb;
 				(session->cb)(wlp);
 			} else {
 				dev_err(dev, "Received expected message from "
 					"unexpected source.  Expected message "
 					"%d or F0 from %02x:%02x, but received "
 					"it from %02x:%02x. Dropping.\n",
 					session->exp_message,
 					session->neighbor_addr.data[1],
 					session->neighbor_addr.data[0],
 					src->data[1], src->data[0]);
 				goto error;
 			}
 		} else {
 			dev_err(dev, "Association already in progress. "
 				"Dropping.\n");
 			goto error;
 		}
 	} else {
 		wlp_direct_assoc_frame(wlp, skb, src);
 	}
 	return;
 error:
 	kfree_skb(skb);
 }

 /*
  * Verify incoming frame is from connected neighbor, prep to pass to WLP client
  *
  * Verification proceeds according to WLP 0.99 [7.3.1]. The source address
  * is used to determine which neighbor is sending the frame and the WSS tag
  * is used to know to which WSS the frame belongs (we only support one WSS
  * so this test is straight forward).
  * With the WSS found we need to ensure that we are connected before
  * allowing the exchange of data frames.
  */
 static
 int wlp_verify_prep_rx_frame(struct wlp *wlp, struct sk_buff *skb,
 			     struct uwb_dev_addr *src)
 {
 	struct device *dev = &wlp->rc->uwb_dev.dev;
 	int result = -EINVAL;
 	struct wlp_eda_node eda_entry;
 	struct wlp_frame_std_abbrv_hdr *hdr = (void *) skb->data;

 	/*verify*/
 	result = wlp_copy_eda_node(&wlp->eda, src, &eda_entry);
 	if (result < 0) {
 		if (printk_ratelimit())
 			dev_err(dev, "WLP: Incoming frame is from unknown "
 				"neighbor %02x:%02x.\n", src->data[1],
 				src->data[0]);
 		goto out;
 	}
 	if (hdr->tag != eda_entry.tag) {
 		if (printk_ratelimit())
 			dev_err(dev, "WLP: Tag of incoming frame from "
 				"%02x:%02x does not match expected tag. "
 				"Received 0x%02x, expected 0x%02x. \n",
 				src->data[1], src->data[0], hdr->tag,
 				eda_entry.tag);
 		result = -EINVAL;
 		goto out;
 	}
 	if (eda_entry.state != WLP_WSS_CONNECTED) {
 		if (printk_ratelimit())
 			dev_err(dev, "WLP: Incoming frame from "
 				"%02x:%02x does is not from connected WSS.\n",
 				src->data[1], src->data[0]);
 		result = -EINVAL;
 		goto out;
 	}
 	/*prep*/
 	skb_pull(skb, sizeof(*hdr));
 out:
 	return result;
 }

 /*
  * Receive a WLP frame from device
  *
  * @returns: 1 if calling function should free the skb
  *           0 if it successfully handled skb and freed it
  *           0 if error occured, will free skb in this case
  */
 int wlp_receive_frame(struct device *dev, struct wlp *wlp, struct sk_buff *skb,
 		      struct uwb_dev_addr *src)
 {
 	unsigned len = skb->len;
 	void *ptr = skb->data;
 	struct wlp_frame_hdr *hdr;
 	int result = 0;

 	if (len < sizeof(*hdr)) {
 		dev_err(dev, "Not enough data to parse WLP header.\n");
 		result = -EINVAL;
 		goto out;
 	}
 	hdr = ptr;
 	if (le16_to_cpu(hdr->mux_hdr) != WLP_PROTOCOL_ID) {
 		dev_err(dev, "Not a WLP frame type.\n");
 		result = -EINVAL;
 		goto out;
 	}
 	switch (hdr->type) {
 	case WLP_FRAME_STANDARD:
 		if (len < sizeof(struct wlp_frame_std_abbrv_hdr)) {
 			dev_err(dev, "Not enough data to parse Standard "
 				"WLP header.\n");
 			goto out;
 		}
 		result = wlp_verify_prep_rx_frame(wlp, skb, src);
 		if (result < 0) {
 			if (printk_ratelimit())
 				dev_err(dev, "WLP: Verification of frame "
 					"from neighbor %02x:%02x failed.\n",
 					src->data[1], src->data[0]);
 			goto out;
 		}
 		result = 1;
 		break;
 	case WLP_FRAME_ABBREVIATED:
 		dev_err(dev, "Abbreviated frame received. FIXME?\n");
 		kfree_skb(skb);
 		break;
 	case WLP_FRAME_CONTROL:
 		dev_err(dev, "Control frame received. FIXME?\n");
 		kfree_skb(skb);
 		break;
 	case WLP_FRAME_ASSOCIATION:
 		if (len < sizeof(struct wlp_frame_assoc)) {
 			dev_err(dev, "Not enough data to parse Association "
 				"WLP header.\n");
 			goto out;
 		}
 		wlp_receive_assoc_frame(wlp, skb, src);
 		break;
 	default:
 		dev_err(dev, "Invalid frame received.\n");
 		result = -EINVAL;
 		break;
 	}
 out:
 	if (result < 0) {
 		kfree_skb(skb);
 		result = 0;
 	}
 	return result;
 }
 EXPORT_SYMBOL_GPL(wlp_receive_frame);


 /*
  * Verify frame from network stack, prepare for further transmission
  *
  * @skb:   the socket buffer that needs to be prepared for transmission (it
  *         is in need of a WLP header). If this is a broadcast frame we take
  *         over the entire transmission.
  *         If it is a unicast the WSS connection should already be established
  *         and transmission will be done by the calling function.
  * @dst:   On return this will contain the device address to which the
  *         frame is destined.
  * @returns: 0 on success no tx : WLP header sucessfully applied to skb buffer,
  *                                calling function can proceed with tx
  *           1 on success with tx : WLP will take over transmission of this
  *                                  frame
  *           <0 on error
  *
  * The network stack (WLP client) is attempting to transmit a frame. We can
  * only transmit data if a local WSS is at least active (connection will be
  * done here if this is a broadcast frame and neighbor also has the WSS
  * active).
  *
  * The frame can be either broadcast or unicast. Broadcast in a WSS is
  * supported via multicast, but we don't support multicast yet (until
  * devices start to support MAB IEs). If a broadcast frame needs to be
  * transmitted it is treated as a unicast frame to each neighbor. In this
  * case the WLP takes over transmission of the skb and returns 1
  * to the caller to indicate so. Also, in this case, if a neighbor has the
  * same WSS activated but is not connected then the WSS connection will be
  * done at this time. The neighbor's virtual address will be learned at
  * this time.
  *
  * The destination address in a unicast frame is the virtual address of the
  * neighbor. This address only becomes known when a WSS connection is
  * established. We thus rely on a broadcast frame to trigger the setup of
  * WSS connections to all neighbors before we are able to send unicast
  * frames to them. This seems reasonable as IP would usually use ARP first
  * before any unicast frames are sent.
  *
  * If we are already connected to the neighbor (neighbor's virtual address
  * is known) we just prepare the WLP header and the caller will continue to
  * send the frame.
  *
  * A failure in this function usually indicates something that cannot be
  * fixed automatically. So, if this function fails (@return < 0) the calling
  * function should not retry to send the frame as it will very likely keep
  * failing.
  *
  */
 int wlp_prepare_tx_frame(struct device *dev, struct wlp *wlp,
 			 struct sk_buff *skb, struct uwb_dev_addr *dst)
 {
 	int result = -EINVAL;
 	struct ethhdr *eth_hdr = (void *) skb->data;

 	if (is_multicast_ether_addr(eth_hdr->h_dest)) {
 		result = wlp_eda_for_each(&wlp->eda, wlp_wss_send_copy, skb);
 		if (result < 0) {
 			if (printk_ratelimit())
 				dev_err(dev, "Unable to handle broadcast "
 					"frame from WLP client.\n");
 			goto out;
 		}
 		dev_kfree_skb_irq(skb);
 		result = 1;
 		/* Frame will be transmitted by WLP. */
 	} else {
 		result = wlp_eda_for_virtual(&wlp->eda, eth_hdr->h_dest, dst,
 					     wlp_wss_prep_hdr, skb);
 		if (unlikely(result < 0)) {
 			if (printk_ratelimit())
 				dev_err(dev, "Unable to prepare "
 					"skb for transmission. \n");
 			goto out;
 		}
 	}
 out:
 	return result;
 }
 EXPORT_SYMBOL_GPL(wlp_prepare_tx_frame);
	/*
	* WiMedia Logical Link Control Protocol (WLP)
	* Message exchange infrastructure
	*
	* Copyright (C) 2007 Intel Corporation
	* Reinette Chatre <reinette.chatre@intel.com>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License version
	* 2 as published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
	* 02110-1301, USA.
	*
	*
	* FIXME: Docs
	*
	*/

	#include <linux/etherdevice.h>
	#include <linux/wlp.h>

	#include "wlp-internal.h"

	/*
	* Direct incoming association msg to correct parsing routine
	*
	* We only expect D1, E1, C1, C3 messages as new. All other incoming
	* association messages should form part of an established session that is
	* handled elsewhere.
	* The handling of these messages often require calling sleeping functions
	* - this cannot be done in interrupt context. We use the kernel's
	* workqueue to handle these messages.
	*/
	static
	void wlp_direct_assoc_frame(struct wlp wlp, struct sk_buff skb,
	struct uwb_dev_addr *src)
	{
	struct device *dev = &wlp->rc->uwb_dev.dev;
	struct wlp_frame_assoc assoc = (void ) skb->data;
	struct wlp_assoc_frame_ctx *frame_ctx;

	frame_ctx = kmalloc(sizeof(*frame_ctx), GFP_ATOMIC);
	if (frame_ctx == NULL) {
	dev_err(dev, "WLP: Unable to allocate memory for association "
	"frame handling.\n");
	kfree_skb(skb);
	return;
	}
	frame_ctx->wlp = wlp;
	frame_ctx->skb = skb;
	frame_ctx->src = *src;
	switch (assoc->type) {
	case WLP_ASSOC_D1:
	INIT_WORK(&frame_ctx->ws, wlp_handle_d1_frame);
	schedule_work(&frame_ctx->ws);
	break;
	case WLP_ASSOC_E1:
	kfree_skb(skb); /* Temporary until we handle it */
	kfree(frame_ctx); /* Temporary until we handle it */
	break;
	case WLP_ASSOC_C1:
	INIT_WORK(&frame_ctx->ws, wlp_handle_c1_frame);
	schedule_work(&frame_ctx->ws);
	break;
	case WLP_ASSOC_C3:
	INIT_WORK(&frame_ctx->ws, wlp_handle_c3_frame);
	schedule_work(&frame_ctx->ws);
	break;
	default:
	dev_err(dev, "Received unexpected association frame. "
	"Type = %d \n", assoc->type);
	kfree_skb(skb);
	kfree(frame_ctx);
	break;
	}
	}

	/*
	* Process incoming association frame
	*
	* Although it could be possible to deal with some incoming association
	* messages without creating a new session we are keeping things simple. We
	* do not accept new association messages if there is a session in progress
	* and the messages do not belong to that session.
	*
	* If an association message arrives that causes the creation of a session
	* (WLP_ASSOC_E1) while we are in the process of creating a session then we
	* rely on the neighbor mutex to protect the data. That is, the new session
	* will not be started until the previous is completed.
	*/
	static
	void wlp_receive_assoc_frame(struct wlp wlp, struct sk_buff skb,
	struct uwb_dev_addr *src)
	{
	struct device *dev = &wlp->rc->uwb_dev.dev;
	struct wlp_frame_assoc assoc = (void ) skb->data;
	struct wlp_session *session = wlp->session;
	u8 version;

	if (wlp_get_version(wlp, &assoc->version, &version,
	sizeof(assoc->version)) < 0)
	goto error;
	if (version != WLP_VERSION) {
	dev_err(dev, "Unsupported WLP version in association "
	"message.\n");
	goto error;
	}
	if (session != NULL) {
	/* Function that created this session is still holding the
	* &wlp->mutex to protect this session. */
	if (assoc->type == session->exp_message \|\|
	assoc->type == WLP_ASSOC_F0) {
	if (!memcmp(&session->neighbor_addr, src,
	sizeof(*src))) {
	session->data = skb;
	(session->cb)(wlp);
	} else {
	dev_err(dev, "Received expected message from "
	"unexpected source. Expected message "
	"%d or F0 from %02x:%02x, but received "
	"it from %02x:%02x. Dropping.\n",
	session->exp_message,
	session->neighbor_addr.data[1],
	session->neighbor_addr.data[0],
	src->data[1], src->data[0]);
	goto error;
	}
	} else {
	dev_err(dev, "Association already in progress. "
	"Dropping.\n");
	goto error;
	}
	} else {
	wlp_direct_assoc_frame(wlp, skb, src);
	}
	return;
	error:
	kfree_skb(skb);
	}

	/*
	* Verify incoming frame is from connected neighbor, prep to pass to WLP client
	*
	* Verification proceeds according to WLP 0.99 [7.3.1]. The source address
	* is used to determine which neighbor is sending the frame and the WSS tag
	* is used to know to which WSS the frame belongs (we only support one WSS
	* so this test is straight forward).
	* With the WSS found we need to ensure that we are connected before
	* allowing the exchange of data frames.
	*/
	static
	int wlp_verify_prep_rx_frame(struct wlp wlp, struct sk_buff skb,
	struct uwb_dev_addr *src)
	{
	struct device *dev = &wlp->rc->uwb_dev.dev;
	int result = -EINVAL;
	struct wlp_eda_node eda_entry;
	struct wlp_frame_std_abbrv_hdr hdr = (void ) skb->data;

	/verify/
	result = wlp_copy_eda_node(&wlp->eda, src, &eda_entry);
	if (result < 0) {
	if (printk_ratelimit())
	dev_err(dev, "WLP: Incoming frame is from unknown "
	"neighbor %02x:%02x.\n", src->data[1],
	src->data[0]);
	goto out;
	}
	if (hdr->tag != eda_entry.tag) {
	if (printk_ratelimit())
	dev_err(dev, "WLP: Tag of incoming frame from "
	"%02x:%02x does not match expected tag. "
	"Received 0x%02x, expected 0x%02x. \n",
	src->data[1], src->data[0], hdr->tag,
	eda_entry.tag);
	result = -EINVAL;
	goto out;
	}
	if (eda_entry.state != WLP_WSS_CONNECTED) {
	if (printk_ratelimit())
	dev_err(dev, "WLP: Incoming frame from "
	"%02x:%02x does is not from connected WSS.\n",
	src->data[1], src->data[0]);
	result = -EINVAL;
	goto out;
	}
	/prep/
	skb_pull(skb, sizeof(*hdr));
	out:
	return result;
	}

	/*
	* Receive a WLP frame from device
	*
	* @returns: 1 if calling function should free the skb
	* 0 if it successfully handled skb and freed it
	* 0 if error occured, will free skb in this case
	*/
	int wlp_receive_frame(struct device dev, struct wlp wlp, struct sk_buff *skb,
	struct uwb_dev_addr *src)
	{
	unsigned len = skb->len;
	void *ptr = skb->data;
	struct wlp_frame_hdr *hdr;
	int result = 0;

	if (len < sizeof(*hdr)) {
	dev_err(dev, "Not enough data to parse WLP header.\n");
	result = -EINVAL;
	goto out;
	}
	hdr = ptr;
	if (le16_to_cpu(hdr->mux_hdr) != WLP_PROTOCOL_ID) {
	dev_err(dev, "Not a WLP frame type.\n");
	result = -EINVAL;
	goto out;
	}
	switch (hdr->type) {
	case WLP_FRAME_STANDARD:
	if (len < sizeof(struct wlp_frame_std_abbrv_hdr)) {
	dev_err(dev, "Not enough data to parse Standard "
	"WLP header.\n");
	goto out;
	}
	result = wlp_verify_prep_rx_frame(wlp, skb, src);
	if (result < 0) {
	if (printk_ratelimit())
	dev_err(dev, "WLP: Verification of frame "
	"from neighbor %02x:%02x failed.\n",
	src->data[1], src->data[0]);
	goto out;
	}
	result = 1;
	break;
	case WLP_FRAME_ABBREVIATED:
	dev_err(dev, "Abbreviated frame received. FIXME?\n");
	kfree_skb(skb);
	break;
	case WLP_FRAME_CONTROL:
	dev_err(dev, "Control frame received. FIXME?\n");
	kfree_skb(skb);
	break;
	case WLP_FRAME_ASSOCIATION:
	if (len < sizeof(struct wlp_frame_assoc)) {
	dev_err(dev, "Not enough data to parse Association "
	"WLP header.\n");
	goto out;
	}
	wlp_receive_assoc_frame(wlp, skb, src);
	break;
	default:
	dev_err(dev, "Invalid frame received.\n");
	result = -EINVAL;
	break;
	}
	out:
	if (result < 0) {
	kfree_skb(skb);
	result = 0;
	}
	return result;
	}
	EXPORT_SYMBOL_GPL(wlp_receive_frame);


	/*
	* Verify frame from network stack, prepare for further transmission
	*
	* @skb: the socket buffer that needs to be prepared for transmission (it
	* is in need of a WLP header). If this is a broadcast frame we take
	* over the entire transmission.
	* If it is a unicast the WSS connection should already be established
	* and transmission will be done by the calling function.
	* @dst: On return this will contain the device address to which the
	* frame is destined.
	* @returns: 0 on success no tx : WLP header sucessfully applied to skb buffer,
	* calling function can proceed with tx
	* 1 on success with tx : WLP will take over transmission of this
	* frame
	* <0 on error
	*
	* The network stack (WLP client) is attempting to transmit a frame. We can
	* only transmit data if a local WSS is at least active (connection will be
	* done here if this is a broadcast frame and neighbor also has the WSS
	* active).
	*
	* The frame can be either broadcast or unicast. Broadcast in a WSS is
	* supported via multicast, but we don't support multicast yet (until
	* devices start to support MAB IEs). If a broadcast frame needs to be
	* transmitted it is treated as a unicast frame to each neighbor. In this
	* case the WLP takes over transmission of the skb and returns 1
	* to the caller to indicate so. Also, in this case, if a neighbor has the
	* same WSS activated but is not connected then the WSS connection will be
	* done at this time. The neighbor's virtual address will be learned at
	* this time.
	*
	* The destination address in a unicast frame is the virtual address of the
	* neighbor. This address only becomes known when a WSS connection is
	* established. We thus rely on a broadcast frame to trigger the setup of
	* WSS connections to all neighbors before we are able to send unicast
	* frames to them. This seems reasonable as IP would usually use ARP first
	* before any unicast frames are sent.
	*
	* If we are already connected to the neighbor (neighbor's virtual address
	* is known) we just prepare the WLP header and the caller will continue to
	* send the frame.
	*
	* A failure in this function usually indicates something that cannot be
	* fixed automatically. So, if this function fails (@return < 0) the calling
	* function should not retry to send the frame as it will very likely keep
	* failing.
	*
	*/
	int wlp_prepare_tx_frame(struct device dev, struct wlp wlp,
	struct sk_buff skb, struct uwb_dev_addr dst)
	{
	int result = -EINVAL;
	struct ethhdr eth_hdr = (void ) skb->data;

	if (is_multicast_ether_addr(eth_hdr->h_dest)) {
	result = wlp_eda_for_each(&wlp->eda, wlp_wss_send_copy, skb);
	if (result < 0) {
	if (printk_ratelimit())
	dev_err(dev, "Unable to handle broadcast "
	"frame from WLP client.\n");
	goto out;
	}
	dev_kfree_skb_irq(skb);
	result = 1;
	/* Frame will be transmitted by WLP. */
	} else {
	result = wlp_eda_for_virtual(&wlp->eda, eth_hdr->h_dest, dst,
	wlp_wss_prep_hdr, skb);
	if (unlikely(result < 0)) {
	if (printk_ratelimit())
	dev_err(dev, "Unable to prepare "
	"skb for transmission. \n");
	goto out;
	}
	}
	out:
	return result;
	}
	EXPORT_SYMBOL_GPL(wlp_prepare_tx_frame);