drivers/net/ethernet/sfc/tx_tso.c - kernel/msm-4.19 - Gitiles

 /****************************************************************************
  * Driver for Solarflare network controllers and boards
  * Copyright 2005-2006 Fen Systems Ltd.
  * Copyright 2005-2015 Solarflare Communications Inc.
  *
  * 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, incorporated herein by reference.
  */

 #include <linux/pci.h>
 #include <linux/tcp.h>
 #include <linux/ip.h>
 #include <linux/in.h>
 #include <linux/ipv6.h>
 #include <linux/slab.h>
 #include <net/ipv6.h>
 #include <linux/if_ether.h>
 #include <linux/highmem.h>
 #include <linux/moduleparam.h>
 #include <linux/cache.h>
 #include "net_driver.h"
 #include "efx.h"
 #include "io.h"
 #include "nic.h"
 #include "tx.h"
 #include "workarounds.h"
 #include "ef10_regs.h"

 /* Efx legacy TCP segmentation acceleration.
  *
  * Utilises firmware support to go faster than GSO (but not as fast as TSOv2).
  *
  * Requires TX checksum offload support.
  */

 #define PTR_DIFF(p1, p2)  ((u8 *)(p1) - (u8 *)(p2))

 /**
  * struct tso_state - TSO state for an SKB
  * @out_len: Remaining length in current segment
  * @seqnum: Current sequence number
  * @ipv4_id: Current IPv4 ID, host endian
  * @packet_space: Remaining space in current packet
  * @dma_addr: DMA address of current position
  * @in_len: Remaining length in current SKB fragment
  * @unmap_len: Length of SKB fragment
  * @unmap_addr: DMA address of SKB fragment
  * @protocol: Network protocol (after any VLAN header)
  * @ip_off: Offset of IP header
  * @tcp_off: Offset of TCP header
  * @header_len: Number of bytes of header
  * @ip_base_len: IPv4 tot_len or IPv6 payload_len, before TCP payload
  * @header_dma_addr: Header DMA address
  * @header_unmap_len: Header DMA mapped length
  *
  * The state used during segmentation.  It is put into this data structure
  * just to make it easy to pass into inline functions.
  */
 struct tso_state {
 	/* Output position */
 	unsigned int out_len;
 	unsigned int seqnum;
 	u16 ipv4_id;
 	unsigned int packet_space;

 	/* Input position */
 	dma_addr_t dma_addr;
 	unsigned int in_len;
 	unsigned int unmap_len;
 	dma_addr_t unmap_addr;

 	__be16 protocol;
 	unsigned int ip_off;
 	unsigned int tcp_off;
 	unsigned int header_len;
 	unsigned int ip_base_len;
 	dma_addr_t header_dma_addr;
 	unsigned int header_unmap_len;
 };

 static inline void prefetch_ptr(struct efx_tx_queue *tx_queue)
 {
 	unsigned int insert_ptr = efx_tx_queue_get_insert_index(tx_queue);
 	char *ptr;

 	ptr = (char *) (tx_queue->buffer + insert_ptr);
 	prefetch(ptr);
 	prefetch(ptr + 0x80);

 	ptr = (char *) (((efx_qword_t *)tx_queue->txd.buf.addr) + insert_ptr);
 	prefetch(ptr);
 	prefetch(ptr + 0x80);
 }

 /**
  * efx_tx_queue_insert - push descriptors onto the TX queue
  * @tx_queue:		Efx TX queue
  * @dma_addr:		DMA address of fragment
  * @len:		Length of fragment
  * @final_buffer:	The final buffer inserted into the queue
  *
  * Push descriptors onto the TX queue.
  */
 static void efx_tx_queue_insert(struct efx_tx_queue *tx_queue,
 				dma_addr_t dma_addr, unsigned int len,
 				struct efx_tx_buffer **final_buffer)
 {
 	struct efx_tx_buffer *buffer;
 	unsigned int dma_len;

 	EFX_BUG_ON_PARANOID(len <= 0);

 	while (1) {
 		buffer = efx_tx_queue_get_insert_buffer(tx_queue);
 		++tx_queue->insert_count;

 		EFX_BUG_ON_PARANOID(tx_queue->insert_count -
 				    tx_queue->read_count >=
 				    tx_queue->efx->txq_entries);

 		buffer->dma_addr = dma_addr;

 		dma_len = tx_queue->efx->type->tx_limit_len(tx_queue,
 				dma_addr, len);

 		/* If there's space for everything this is our last buffer. */
 		if (dma_len >= len)
 			break;

 		buffer->len = dma_len;
 		buffer->flags = EFX_TX_BUF_CONT;
 		dma_addr += dma_len;
 		len -= dma_len;
 	}

 	EFX_BUG_ON_PARANOID(!len);
 	buffer->len = len;
 	*final_buffer = buffer;
 }

 /*
  * Verify that our various assumptions about sk_buffs and the conditions
  * under which TSO will be attempted hold true.  Return the protocol number.
  */
 static __be16 efx_tso_check_protocol(struct sk_buff *skb)
 {
 	__be16 protocol = skb->protocol;

 	EFX_BUG_ON_PARANOID(((struct ethhdr *)skb->data)->h_proto !=
 			    protocol);
 	if (protocol == htons(ETH_P_8021Q)) {
 		struct vlan_ethhdr *veh = (struct vlan_ethhdr *)skb->data;

 		protocol = veh->h_vlan_encapsulated_proto;
 	}

 	if (protocol == htons(ETH_P_IP)) {
 		EFX_BUG_ON_PARANOID(ip_hdr(skb)->protocol != IPPROTO_TCP);
 	} else {
 		EFX_BUG_ON_PARANOID(protocol != htons(ETH_P_IPV6));
 		EFX_BUG_ON_PARANOID(ipv6_hdr(skb)->nexthdr != NEXTHDR_TCP);
 	}
 	EFX_BUG_ON_PARANOID((PTR_DIFF(tcp_hdr(skb), skb->data)
 			     + (tcp_hdr(skb)->doff << 2u)) >
 			    skb_headlen(skb));

 	return protocol;
 }


 /* Parse the SKB header and initialise state. */
 static int tso_start(struct tso_state *st, struct efx_nic *efx,
 		     struct efx_tx_queue *tx_queue,
 		     const struct sk_buff *skb)
 {
 	struct device *dma_dev = &efx->pci_dev->dev;
 	unsigned int header_len, in_len;
 	dma_addr_t dma_addr;

 	st->ip_off = skb_network_header(skb) - skb->data;
 	st->tcp_off = skb_transport_header(skb) - skb->data;
 	header_len = st->tcp_off + (tcp_hdr(skb)->doff << 2u);
 	in_len = skb_headlen(skb) - header_len;
 	st->header_len = header_len;
 	st->in_len = in_len;
 	if (st->protocol == htons(ETH_P_IP)) {
 		st->ip_base_len = st->header_len - st->ip_off;
 		st->ipv4_id = ntohs(ip_hdr(skb)->id);
 	} else {
 		st->ip_base_len = st->header_len - st->tcp_off;
 		st->ipv4_id = 0;
 	}
 	st->seqnum = ntohl(tcp_hdr(skb)->seq);

 	EFX_BUG_ON_PARANOID(tcp_hdr(skb)->urg);
 	EFX_BUG_ON_PARANOID(tcp_hdr(skb)->syn);
 	EFX_BUG_ON_PARANOID(tcp_hdr(skb)->rst);

 	st->out_len = skb->len - header_len;

 	dma_addr = dma_map_single(dma_dev, skb->data,
 				  skb_headlen(skb), DMA_TO_DEVICE);
 	st->header_dma_addr = dma_addr;
 	st->header_unmap_len = skb_headlen(skb);
 	st->dma_addr = dma_addr + header_len;
 	st->unmap_len = 0;

 	return unlikely(dma_mapping_error(dma_dev, dma_addr)) ? -ENOMEM : 0;
 }

 static int tso_get_fragment(struct tso_state *st, struct efx_nic *efx,
 			    skb_frag_t *frag)
 {
 	st->unmap_addr = skb_frag_dma_map(&efx->pci_dev->dev, frag, 0,
 					  skb_frag_size(frag), DMA_TO_DEVICE);
 	if (likely(!dma_mapping_error(&efx->pci_dev->dev, st->unmap_addr))) {
 		st->unmap_len = skb_frag_size(frag);
 		st->in_len = skb_frag_size(frag);
 		st->dma_addr = st->unmap_addr;
 		return 0;
 	}
 	return -ENOMEM;
 }


 /**
  * tso_fill_packet_with_fragment - form descriptors for the current fragment
  * @tx_queue:		Efx TX queue
  * @skb:		Socket buffer
  * @st:			TSO state
  *
  * Form descriptors for the current fragment, until we reach the end
  * of fragment or end-of-packet.
  */
 static void tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue,
 					  const struct sk_buff *skb,
 					  struct tso_state *st)
 {
 	struct efx_tx_buffer *buffer;
 	int n;

 	if (st->in_len == 0)
 		return;
 	if (st->packet_space == 0)
 		return;

 	EFX_BUG_ON_PARANOID(st->in_len <= 0);
 	EFX_BUG_ON_PARANOID(st->packet_space <= 0);

 	n = min(st->in_len, st->packet_space);

 	st->packet_space -= n;
 	st->out_len -= n;
 	st->in_len -= n;

 	efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);

 	if (st->out_len == 0) {
 		/* Transfer ownership of the skb */
 		buffer->skb = skb;
 		buffer->flags = EFX_TX_BUF_SKB;
 	} else if (st->packet_space != 0) {
 		buffer->flags = EFX_TX_BUF_CONT;
 	}

 	if (st->in_len == 0) {
 		/* Transfer ownership of the DMA mapping */
 		buffer->unmap_len = st->unmap_len;
 		buffer->dma_offset = buffer->unmap_len - buffer->len;
 		st->unmap_len = 0;
 	}

 	st->dma_addr += n;
 }


 #define TCP_FLAGS_OFFSET 13

 /**
  * tso_start_new_packet - generate a new header and prepare for the new packet
  * @tx_queue:		Efx TX queue
  * @skb:		Socket buffer
  * @st:			TSO state
  *
  * Generate a new header and prepare for the new packet.  Return 0 on
  * success, or -%ENOMEM if failed to alloc header, or other negative error.
  */
 static int tso_start_new_packet(struct efx_tx_queue *tx_queue,
 				const struct sk_buff *skb,
 				struct tso_state *st)
 {
 	struct efx_tx_buffer *buffer =
 		efx_tx_queue_get_insert_buffer(tx_queue);
 	bool is_last = st->out_len <= skb_shinfo(skb)->gso_size;
 	u8 tcp_flags_mask, tcp_flags;

 	if (!is_last) {
 		st->packet_space = skb_shinfo(skb)->gso_size;
 		tcp_flags_mask = 0x09; /* mask out FIN and PSH */
 	} else {
 		st->packet_space = st->out_len;
 		tcp_flags_mask = 0x00;
 	}

 	if (WARN_ON(!st->header_unmap_len))
 		return -EINVAL;
 	/* Send the original headers with a TSO option descriptor
 	 * in front
 	 */
 	tcp_flags = ((u8 *)tcp_hdr(skb))[TCP_FLAGS_OFFSET] & ~tcp_flags_mask;

 	buffer->flags = EFX_TX_BUF_OPTION;
 	buffer->len = 0;
 	buffer->unmap_len = 0;
 	EFX_POPULATE_QWORD_5(buffer->option,
 			     ESF_DZ_TX_DESC_IS_OPT, 1,
 			     ESF_DZ_TX_OPTION_TYPE,
 			     ESE_DZ_TX_OPTION_DESC_TSO,
 			     ESF_DZ_TX_TSO_TCP_FLAGS, tcp_flags,
 			     ESF_DZ_TX_TSO_IP_ID, st->ipv4_id,
 			     ESF_DZ_TX_TSO_TCP_SEQNO, st->seqnum);
 	++tx_queue->insert_count;

 	/* We mapped the headers in tso_start().  Unmap them
 	 * when the last segment is completed.
 	 */
 	buffer = efx_tx_queue_get_insert_buffer(tx_queue);
 	buffer->dma_addr = st->header_dma_addr;
 	buffer->len = st->header_len;
 	if (is_last) {
 		buffer->flags = EFX_TX_BUF_CONT | EFX_TX_BUF_MAP_SINGLE;
 		buffer->unmap_len = st->header_unmap_len;
 		buffer->dma_offset = 0;
 		/* Ensure we only unmap them once in case of a
 		 * later DMA mapping error and rollback
 		 */
 		st->header_unmap_len = 0;
 	} else {
 		buffer->flags = EFX_TX_BUF_CONT;
 		buffer->unmap_len = 0;
 	}
 	++tx_queue->insert_count;

 	st->seqnum += skb_shinfo(skb)->gso_size;

 	/* Linux leaves suitable gaps in the IP ID space for us to fill. */
 	++st->ipv4_id;

 	return 0;
 }

 /**
  * efx_enqueue_skb_tso - segment and transmit a TSO socket buffer
  * @tx_queue:		Efx TX queue
  * @skb:		Socket buffer
  * @data_mapped:        Did we map the data? Always set to true
  *                      by this on success.
  *
  * Context: You must hold netif_tx_lock() to call this function.
  *
  * Add socket buffer @skb to @tx_queue, doing TSO or return != 0 if
  * @skb was not enqueued.  @skb is consumed unless return value is
  * %EINVAL.
  */
 int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
 			struct sk_buff *skb,
 			bool *data_mapped)
 {
 	struct efx_nic *efx = tx_queue->efx;
 	int frag_i, rc;
 	struct tso_state state;

 	if (tx_queue->tso_version != 1)
 		return -EINVAL;

 	prefetch(skb->data);

 	/* Find the packet protocol and sanity-check it */
 	state.protocol = efx_tso_check_protocol(skb);

 	EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);

 	rc = tso_start(&state, efx, tx_queue, skb);
 	if (rc)
 		goto fail;

 	if (likely(state.in_len == 0)) {
 		/* Grab the first payload fragment. */
 		EFX_BUG_ON_PARANOID(skb_shinfo(skb)->nr_frags < 1);
 		frag_i = 0;
 		rc = tso_get_fragment(&state, efx,
 				      skb_shinfo(skb)->frags + frag_i);
 		if (rc)
 			goto fail;
 	} else {
 		/* Payload starts in the header area. */
 		frag_i = -1;
 	}

 	rc = tso_start_new_packet(tx_queue, skb, &state);
 	if (rc)
 		goto fail;

 	prefetch_ptr(tx_queue);

 	while (1) {
 		tso_fill_packet_with_fragment(tx_queue, skb, &state);

 		/* Move onto the next fragment? */
 		if (state.in_len == 0) {
 			if (++frag_i >= skb_shinfo(skb)->nr_frags)
 				/* End of payload reached. */
 				break;
 			rc = tso_get_fragment(&state, efx,
 					      skb_shinfo(skb)->frags + frag_i);
 			if (rc)
 				goto fail;
 		}

 		/* Start at new packet? */
 		if (state.packet_space == 0) {
 			rc = tso_start_new_packet(tx_queue, skb, &state);
 			if (rc)
 				goto fail;
 		}
 	}

 	*data_mapped = true;

 	return 0;

 fail:
 	if (rc == -ENOMEM)
 		netif_err(efx, tx_err, efx->net_dev,
 			  "Out of memory for TSO headers, or DMA mapping error\n");
 	else
 		netif_err(efx, tx_err, efx->net_dev, "TSO failed, rc = %d\n", rc);

 	/* Free the DMA mapping we were in the process of writing out */
 	if (state.unmap_len) {
 		dma_unmap_page(&efx->pci_dev->dev, state.unmap_addr,
 			       state.unmap_len, DMA_TO_DEVICE);
 	}

 	/* Free the header DMA mapping */
 	if (state.header_unmap_len)
 		dma_unmap_single(&efx->pci_dev->dev, state.header_dma_addr,
 				 state.header_unmap_len, DMA_TO_DEVICE);

 	return rc;
 }
	/****************************************************************************
	* Driver for Solarflare network controllers and boards
	* Copyright 2005-2006 Fen Systems Ltd.
	* Copyright 2005-2015 Solarflare Communications Inc.
	*
	* 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, incorporated herein by reference.
	*/

	#include <linux/pci.h>
	#include <linux/tcp.h>
	#include <linux/ip.h>
	#include <linux/in.h>
	#include <linux/ipv6.h>
	#include <linux/slab.h>
	#include <net/ipv6.h>
	#include <linux/if_ether.h>
	#include <linux/highmem.h>
	#include <linux/moduleparam.h>
	#include <linux/cache.h>
	#include "net_driver.h"
	#include "efx.h"
	#include "io.h"
	#include "nic.h"
	#include "tx.h"
	#include "workarounds.h"
	#include "ef10_regs.h"

	/* Efx legacy TCP segmentation acceleration.
	*
	* Utilises firmware support to go faster than GSO (but not as fast as TSOv2).
	*
	* Requires TX checksum offload support.
	*/

	#define PTR_DIFF(p1, p2) ((u8 )(p1) - (u8 )(p2))

	/**
	* struct tso_state - TSO state for an SKB
	* @out_len: Remaining length in current segment
	* @seqnum: Current sequence number
	* @ipv4_id: Current IPv4 ID, host endian
	* @packet_space: Remaining space in current packet
	* @dma_addr: DMA address of current position
	* @in_len: Remaining length in current SKB fragment
	* @unmap_len: Length of SKB fragment
	* @unmap_addr: DMA address of SKB fragment
	* @protocol: Network protocol (after any VLAN header)
	* @ip_off: Offset of IP header
	* @tcp_off: Offset of TCP header
	* @header_len: Number of bytes of header
	* @ip_base_len: IPv4 tot_len or IPv6 payload_len, before TCP payload
	* @header_dma_addr: Header DMA address
	* @header_unmap_len: Header DMA mapped length
	*
	* The state used during segmentation. It is put into this data structure
	* just to make it easy to pass into inline functions.
	*/
	struct tso_state {
	/* Output position */
	unsigned int out_len;
	unsigned int seqnum;
	u16 ipv4_id;
	unsigned int packet_space;

	/* Input position */
	dma_addr_t dma_addr;
	unsigned int in_len;
	unsigned int unmap_len;
	dma_addr_t unmap_addr;

	__be16 protocol;
	unsigned int ip_off;
	unsigned int tcp_off;
	unsigned int header_len;
	unsigned int ip_base_len;
	dma_addr_t header_dma_addr;
	unsigned int header_unmap_len;
	};

	static inline void prefetch_ptr(struct efx_tx_queue *tx_queue)
	{
	unsigned int insert_ptr = efx_tx_queue_get_insert_index(tx_queue);
	char *ptr;

	ptr = (char *) (tx_queue->buffer + insert_ptr);
	prefetch(ptr);
	prefetch(ptr + 0x80);

	ptr = (char ) (((efx_qword_t )tx_queue->txd.buf.addr) + insert_ptr);
	prefetch(ptr);
	prefetch(ptr + 0x80);
	}

	/**
	* efx_tx_queue_insert - push descriptors onto the TX queue
	* @tx_queue: Efx TX queue
	* @dma_addr: DMA address of fragment
	* @len: Length of fragment
	* @final_buffer: The final buffer inserted into the queue
	*
	* Push descriptors onto the TX queue.
	*/
	static void efx_tx_queue_insert(struct efx_tx_queue *tx_queue,
	dma_addr_t dma_addr, unsigned int len,
	struct efx_tx_buffer **final_buffer)
	{
	struct efx_tx_buffer *buffer;
	unsigned int dma_len;

	EFX_BUG_ON_PARANOID(len <= 0);

	while (1) {
	buffer = efx_tx_queue_get_insert_buffer(tx_queue);
	++tx_queue->insert_count;

	EFX_BUG_ON_PARANOID(tx_queue->insert_count -
	tx_queue->read_count >=
	tx_queue->efx->txq_entries);

	buffer->dma_addr = dma_addr;

	dma_len = tx_queue->efx->type->tx_limit_len(tx_queue,
	dma_addr, len);

	/* If there's space for everything this is our last buffer. */
	if (dma_len >= len)
	break;

	buffer->len = dma_len;
	buffer->flags = EFX_TX_BUF_CONT;
	dma_addr += dma_len;
	len -= dma_len;
	}

	EFX_BUG_ON_PARANOID(!len);
	buffer->len = len;
	*final_buffer = buffer;
	}

	/*
	* Verify that our various assumptions about sk_buffs and the conditions
	* under which TSO will be attempted hold true. Return the protocol number.
	*/
	static __be16 efx_tso_check_protocol(struct sk_buff *skb)
	{
	__be16 protocol = skb->protocol;

	EFX_BUG_ON_PARANOID(((struct ethhdr *)skb->data)->h_proto !=
	protocol);
	if (protocol == htons(ETH_P_8021Q)) {
	struct vlan_ethhdr veh = (struct vlan_ethhdr )skb->data;

	protocol = veh->h_vlan_encapsulated_proto;
	}

	if (protocol == htons(ETH_P_IP)) {
	EFX_BUG_ON_PARANOID(ip_hdr(skb)->protocol != IPPROTO_TCP);
	} else {
	EFX_BUG_ON_PARANOID(protocol != htons(ETH_P_IPV6));
	EFX_BUG_ON_PARANOID(ipv6_hdr(skb)->nexthdr != NEXTHDR_TCP);
	}
	EFX_BUG_ON_PARANOID((PTR_DIFF(tcp_hdr(skb), skb->data)
	+ (tcp_hdr(skb)->doff << 2u)) >
	skb_headlen(skb));

	return protocol;
	}


	/* Parse the SKB header and initialise state. */
	static int tso_start(struct tso_state st, struct efx_nic efx,
	struct efx_tx_queue *tx_queue,
	const struct sk_buff *skb)
	{
	struct device *dma_dev = &efx->pci_dev->dev;
	unsigned int header_len, in_len;
	dma_addr_t dma_addr;

	st->ip_off = skb_network_header(skb) - skb->data;
	st->tcp_off = skb_transport_header(skb) - skb->data;
	header_len = st->tcp_off + (tcp_hdr(skb)->doff << 2u);
	in_len = skb_headlen(skb) - header_len;
	st->header_len = header_len;
	st->in_len = in_len;
	if (st->protocol == htons(ETH_P_IP)) {
	st->ip_base_len = st->header_len - st->ip_off;
	st->ipv4_id = ntohs(ip_hdr(skb)->id);
	} else {
	st->ip_base_len = st->header_len - st->tcp_off;
	st->ipv4_id = 0;
	}
	st->seqnum = ntohl(tcp_hdr(skb)->seq);

	EFX_BUG_ON_PARANOID(tcp_hdr(skb)->urg);
	EFX_BUG_ON_PARANOID(tcp_hdr(skb)->syn);
	EFX_BUG_ON_PARANOID(tcp_hdr(skb)->rst);

	st->out_len = skb->len - header_len;

	dma_addr = dma_map_single(dma_dev, skb->data,
	skb_headlen(skb), DMA_TO_DEVICE);
	st->header_dma_addr = dma_addr;
	st->header_unmap_len = skb_headlen(skb);
	st->dma_addr = dma_addr + header_len;
	st->unmap_len = 0;

	return unlikely(dma_mapping_error(dma_dev, dma_addr)) ? -ENOMEM : 0;
	}

	static int tso_get_fragment(struct tso_state st, struct efx_nic efx,
	skb_frag_t *frag)
	{
	st->unmap_addr = skb_frag_dma_map(&efx->pci_dev->dev, frag, 0,
	skb_frag_size(frag), DMA_TO_DEVICE);
	if (likely(!dma_mapping_error(&efx->pci_dev->dev, st->unmap_addr))) {
	st->unmap_len = skb_frag_size(frag);
	st->in_len = skb_frag_size(frag);
	st->dma_addr = st->unmap_addr;
	return 0;
	}
	return -ENOMEM;
	}


	/**
	* tso_fill_packet_with_fragment - form descriptors for the current fragment
	* @tx_queue: Efx TX queue
	* @skb: Socket buffer
	* @st: TSO state
	*
	* Form descriptors for the current fragment, until we reach the end
	* of fragment or end-of-packet.
	*/
	static void tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue,
	const struct sk_buff *skb,
	struct tso_state *st)
	{
	struct efx_tx_buffer *buffer;
	int n;

	if (st->in_len == 0)
	return;
	if (st->packet_space == 0)
	return;

	EFX_BUG_ON_PARANOID(st->in_len <= 0);
	EFX_BUG_ON_PARANOID(st->packet_space <= 0);

	n = min(st->in_len, st->packet_space);

	st->packet_space -= n;
	st->out_len -= n;
	st->in_len -= n;

	efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);

	if (st->out_len == 0) {
	/* Transfer ownership of the skb */
	buffer->skb = skb;
	buffer->flags = EFX_TX_BUF_SKB;
	} else if (st->packet_space != 0) {
	buffer->flags = EFX_TX_BUF_CONT;
	}

	if (st->in_len == 0) {
	/* Transfer ownership of the DMA mapping */
	buffer->unmap_len = st->unmap_len;
	buffer->dma_offset = buffer->unmap_len - buffer->len;
	st->unmap_len = 0;
	}

	st->dma_addr += n;
	}


	#define TCP_FLAGS_OFFSET 13

	/**
	* tso_start_new_packet - generate a new header and prepare for the new packet
	* @tx_queue: Efx TX queue
	* @skb: Socket buffer
	* @st: TSO state
	*
	* Generate a new header and prepare for the new packet. Return 0 on
	* success, or -%ENOMEM if failed to alloc header, or other negative error.
	*/
	static int tso_start_new_packet(struct efx_tx_queue *tx_queue,
	const struct sk_buff *skb,
	struct tso_state *st)
	{
	struct efx_tx_buffer *buffer =
	efx_tx_queue_get_insert_buffer(tx_queue);
	bool is_last = st->out_len <= skb_shinfo(skb)->gso_size;
	u8 tcp_flags_mask, tcp_flags;

	if (!is_last) {
	st->packet_space = skb_shinfo(skb)->gso_size;
	tcp_flags_mask = 0x09; /* mask out FIN and PSH */
	} else {
	st->packet_space = st->out_len;
	tcp_flags_mask = 0x00;
	}

	if (WARN_ON(!st->header_unmap_len))
	return -EINVAL;
	/* Send the original headers with a TSO option descriptor
	* in front
	*/
	tcp_flags = ((u8 *)tcp_hdr(skb))[TCP_FLAGS_OFFSET] & ~tcp_flags_mask;

	buffer->flags = EFX_TX_BUF_OPTION;
	buffer->len = 0;
	buffer->unmap_len = 0;
	EFX_POPULATE_QWORD_5(buffer->option,
	ESF_DZ_TX_DESC_IS_OPT, 1,
	ESF_DZ_TX_OPTION_TYPE,
	ESE_DZ_TX_OPTION_DESC_TSO,
	ESF_DZ_TX_TSO_TCP_FLAGS, tcp_flags,
	ESF_DZ_TX_TSO_IP_ID, st->ipv4_id,
	ESF_DZ_TX_TSO_TCP_SEQNO, st->seqnum);
	++tx_queue->insert_count;

	/* We mapped the headers in tso_start(). Unmap them
	* when the last segment is completed.
	*/
	buffer = efx_tx_queue_get_insert_buffer(tx_queue);
	buffer->dma_addr = st->header_dma_addr;
	buffer->len = st->header_len;
	if (is_last) {
	buffer->flags = EFX_TX_BUF_CONT \| EFX_TX_BUF_MAP_SINGLE;
	buffer->unmap_len = st->header_unmap_len;
	buffer->dma_offset = 0;
	/* Ensure we only unmap them once in case of a
	* later DMA mapping error and rollback
	*/
	st->header_unmap_len = 0;
	} else {
	buffer->flags = EFX_TX_BUF_CONT;
	buffer->unmap_len = 0;
	}
	++tx_queue->insert_count;

	st->seqnum += skb_shinfo(skb)->gso_size;

	/* Linux leaves suitable gaps in the IP ID space for us to fill. */
	++st->ipv4_id;

	return 0;
	}

	/**
	* efx_enqueue_skb_tso - segment and transmit a TSO socket buffer
	* @tx_queue: Efx TX queue
	* @skb: Socket buffer
	* @data_mapped: Did we map the data? Always set to true
	* by this on success.
	*
	* Context: You must hold netif_tx_lock() to call this function.
	*
	* Add socket buffer @skb to @tx_queue, doing TSO or return != 0 if
	* @skb was not enqueued. @skb is consumed unless return value is
	* %EINVAL.
	*/
	int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
	struct sk_buff *skb,
	bool *data_mapped)
	{
	struct efx_nic *efx = tx_queue->efx;
	int frag_i, rc;
	struct tso_state state;

	if (tx_queue->tso_version != 1)
	return -EINVAL;

	prefetch(skb->data);

	/* Find the packet protocol and sanity-check it */
	state.protocol = efx_tso_check_protocol(skb);

	EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);

	rc = tso_start(&state, efx, tx_queue, skb);
	if (rc)
	goto fail;

	if (likely(state.in_len == 0)) {
	/* Grab the first payload fragment. */
	EFX_BUG_ON_PARANOID(skb_shinfo(skb)->nr_frags < 1);
	frag_i = 0;
	rc = tso_get_fragment(&state, efx,
	skb_shinfo(skb)->frags + frag_i);
	if (rc)
	goto fail;
	} else {
	/* Payload starts in the header area. */
	frag_i = -1;
	}

	rc = tso_start_new_packet(tx_queue, skb, &state);
	if (rc)
	goto fail;

	prefetch_ptr(tx_queue);

	while (1) {
	tso_fill_packet_with_fragment(tx_queue, skb, &state);

	/* Move onto the next fragment? */
	if (state.in_len == 0) {
	if (++frag_i >= skb_shinfo(skb)->nr_frags)
	/* End of payload reached. */
	break;
	rc = tso_get_fragment(&state, efx,
	skb_shinfo(skb)->frags + frag_i);
	if (rc)
	goto fail;
	}

	/* Start at new packet? */
	if (state.packet_space == 0) {
	rc = tso_start_new_packet(tx_queue, skb, &state);
	if (rc)
	goto fail;
	}
	}

	*data_mapped = true;

	return 0;

	fail:
	if (rc == -ENOMEM)
	netif_err(efx, tx_err, efx->net_dev,
	"Out of memory for TSO headers, or DMA mapping error\n");
	else
	netif_err(efx, tx_err, efx->net_dev, "TSO failed, rc = %d\n", rc);

	/* Free the DMA mapping we were in the process of writing out */
	if (state.unmap_len) {
	dma_unmap_page(&efx->pci_dev->dev, state.unmap_addr,
	state.unmap_len, DMA_TO_DEVICE);
	}

	/* Free the header DMA mapping */
	if (state.header_unmap_len)
	dma_unmap_single(&efx->pci_dev->dev, state.header_dma_addr,
	state.header_unmap_len, DMA_TO_DEVICE);

	return rc;
	}