Patchwork [23/39] i2400m: handling of the data/control transmission path

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Submitter Inaky Perez-Gonzalez
Date Nov. 24, 2008, 9:50 p.m.
Message ID <983e0c02aa9907b88a056425656a591377ee74ca.1227562829.git.inaky@linux.intel.com>
Download mbox | patch
Permalink /patch/10508/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

Inaky Perez-Gonzalez - Nov. 24, 2008, 9:50 p.m.
Implements data transmission to the device; this is done through a
software FIFO, as data/control frames can be coalesced (while the
device is reading the previous tx transaction, others accumulate).

A FIFO is used because at the end it is resource-cheaper that trying
to implement scatter/gather over USB. As well, most traffic is going
to be download (vs upload).

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
---
 drivers/net/wimax/i2400m/tx.c |  817 +++++++++++++++++++++++++++++++++++++++++
 1 files changed, 817 insertions(+), 0 deletions(-)
 create mode 100644 drivers/net/wimax/i2400m/tx.c

Patch

diff --git a/drivers/net/wimax/i2400m/tx.c b/drivers/net/wimax/i2400m/tx.c
new file mode 100644
index 0000000..613a88f
--- /dev/null
+++ b/drivers/net/wimax/i2400m/tx.c
@@ -0,0 +1,817 @@ 
+/*
+ * Intel Wireless WiMAX Connection 2400m
+ * Generic (non-bus specific) TX handling
+ *
+ *
+ * Copyright (C) 2007-2008 Intel Corporation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   * Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in
+ *     the documentation and/or other materials provided with the
+ *     distribution.
+ *   * Neither the name of Intel Corporation nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ *
+ * Intel Corporation <linux-wimax@intel.com>
+ * Yanir Lubetkin <yanirx.lubetkin@intel.com>
+ *  - Initial implementation
+ *
+ * Intel Corporation <linux-wimax@intel.com>
+ * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
+ *  - Rewritten to use a single FIFO to lower the memory allocation
+ *    pressure and optimize cache hits when copying to the queue, as
+ *    well as splitting out bus-specific code.
+ *
+ *
+ * Implements data transmission to the device; this is done through a
+ * software FIFO, as data/control frames can be coalesced (while the
+ * device is reading the previous tx transaction, others accumulate).
+ *
+ * A FIFO is used because at the end it is resource-cheaper that trying
+ * to implement scatter/gather over USB. As well, most traffic is going
+ * to be download (vs upload).
+ *
+ * The format for sending/receiving data to/from the i2400m is
+ * described in detail in rx.c:PROTOCOL FORMAT. In here we implement
+ * the transmission of that. This is split between a bus-independent
+ * part that just prepares everything and a bus-specific part that
+ * does the actual transmission over the bus to the device (in the
+ * bus-specific driver).
+ *
+ *
+ * The general format of a device-host transaction is MSG-HDR, PLD1,
+ * PLD2...PLDN, PL1, PL2,...PLN, PADDING.
+ *
+ * Because we need the send payload descriptors and then payloads and
+ * because it is kind of expensive to do scatterlists in USB (one URB
+ * per node), it becomes cheaper to append all the data to a FIFO
+ * (copying to a FIFO potentially in cache is cheaper).
+ *
+ * Then the bus-specific code takes the parts of that FIFO that are
+ * written and passes them to the device.
+ *
+ * So the concepts to keep in mind there are:
+ *
+ * We use a FIFO to queue the data in a linear buffer. We first append
+ * a MSG-HDR, space for I2400M_TX_PLD_MAX payload descriptors and then
+ * go appending payloads until we run out of space or of payload
+ * descriptors. Then we append padding to make the whole transaction a
+ * multiple of i2400m->bus_tx_block_size (as defined by the bus layer).
+ *
+ * - A TX message: a combination of a message header, payload
+ *   descriptors and payloads.
+ *
+ *     Open: it is marked as active (i2400m->tx_msg is valid) and we
+ *       can keep adding payloads to it.
+ *
+ *     Closed: we are not appending more payloads to this TX message
+ *       (exahusted space in the queue, too many payloads or
+ *       whichever).  We have appended padding so the whole message
+ *       length is aligned to i2400m->bus_tx_block_size (as set by the
+ *       bus/transport layer).
+ *
+ * - Most of the time we keep a TX message open to which we append
+ *   payloads.
+ *
+ * - If we are going to append and there is no more space (we are at
+ *   the end of the FIFO), we close the message, mark the rest of the
+ *   FIFO space unusable (skip_tail), create a new message at the
+ *   beginning of the FIFO (if there is space) and append the message
+ *   there.
+ *
+ *   This is because we need to give linear TX messages to the bus
+ *   engine. So we don't write a message to the remaining FIFO space
+ *   until the tail and continue at the head of it.
+ *
+ * - We overload one of the fields in the message header to use it as
+ *   'size' of the TX message, so we can iterate over them. It also
+ *   contains a flag that indicates if we have to skip it or not.
+ *   When we send the buffer, we update that to its real on-the-wire
+ *   value.
+ *
+ * - The MSG-HDR PLD1...PLD2 stuff has to be a size multiple of 16.
+ *
+ *   It follows that if MSG-HDR says we have N messages, the whole
+ *   header + descriptors is 16 + 4*N; for those to be a multiple of
+ *   16, it follows that N can be 4, 8, 12, ... (32, 48, 64, 80...
+ *   bytes).
+ *
+ *   So if we have only 1 payload, we have to submit a header that in
+ *   all truth has space for 4.
+ *
+ *   The implication is that we reserve space for 12 (64 bytes); but
+ *   if we fill up only (eg) 2, our header becomes 32 bytes only. So
+ *   the TX engine has to shift those 32 bytes of msg header and 2
+ *   payloads and padding so that right after it the payloads start
+ *   and the TX engine has to know about that.
+ *
+ *   It is cheaper to move the header up than the whole payloads down.
+ *
+ *   We do this in i2400m_tx_close(). See 'i2400m_msg_hdr->offset'.
+ *
+ * - Each payload has to be size-padded to 16 bytes; before appending
+ *   it, we just do it.
+ *
+ * - The whole message has to be padded to i2400m->bus_tx_block_size;
+ *   we do this at close time. Thus, when reserving space for the
+ *   payload, we always make sure there is also free space for this
+ *   padding that sooner or later will happen.
+ *
+ * When we append a message, we tell the bus specific code to kick in
+ * TXs. It will TX (in parallel) until the buffer is exhausted--hence
+ * the lockin we do. The TX code will only send a TX message at the
+ * time (which remember, might contain more than one payload). Of
+ * course, when the bus-specific driver attempts to TX a message that
+ * is still open, it gets closed first.
+ *
+ * Gee, this is messy; well a picture. In the example below we have a
+ * partially full FIFO, with a closed message ready to be delivered
+ * (with a moved message header to make sure it is size-aligned to
+ * 16), TAIL room that was unusable (and thus is marked with a message
+ * header that says 'skip this') and at the head of the buffer, an
+ * imcomplete message with a couple of payloads.
+ *
+ * N   ___________________________________________________
+ *    |                                                   |
+ *    |     TAIL room                                     |
+ *    |                                                   |
+ *    |  msg_hdr to skip (size |= 0x80000)                |
+ *    |---------------------------------------------------|-------
+ *    |                                                   |  /|\
+ *    |                                                   |   |
+ *    |  TX message padding                               |   |
+ *    |                                                   |   |
+ *    |                                                   |   |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|   |
+ *    |                                                   |   |
+ *    |  payload 1                                        |   |
+ *    |                                                   | N * tx_block_size
+ *    |                                                   |   |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|   |
+ *    |                                                   |   |
+ *    |  payload 1                                        |   |
+ *    |                                                   |   |
+ *    |                                                   |   |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|- -|- - - -
+ *    |  padding 3                  /|\                   |   |   /|\
+ *    |  padding 2                   |                    |   |    |
+ *    |  pld 1                32 bytes (2 * 16)           |   |    |
+ *    |  pld 0                       |                    |   |    |
+ *    |  moved msg_hdr              \|/                   |  \|/   |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|- - -   |
+ *    |                                                   |    _PLD_SIZE
+ *    |  unused                                           |        |
+ *    |                                                   |        |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|        |
+ *    |  msg_hdr (size X)       [this message is closed]  |       \|/
+ *    |===================================================|========== <=== OUT
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |          Free rooom                               |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |===================================================|========== <=== IN
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |                                                   |
+ *    |  payload 1                                        |
+ *    |                                                   |
+ *    |                                                   |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|
+ *    |                                                   |
+ *    |  payload 0                                        |
+ *    |                                                   |
+ *    |                                                   |
+ *    |- - - - - - - - - - - - - - - - - - - - - - - - - -|
+ *    |  pld 11                     /|\                   |
+ *    |  ...                         |                    |
+ *    |  pld 1                64 bytes (2 * 16)           |
+ *    |  pld 0                       |                    |
+ *    |  msg_hdr (size X)           \|/ [message is open] |
+ * 0   ---------------------------------------------------
+ *
+ *
+ * ROADMAP
+ *
+ * i2400m_tx_setup()           Called by i2400m_setup
+ * i2400m_tx_release()         Called by i2400m_release()
+ *
+ *  i2400m_tx()                 Called to send data or control frames
+ *    i2400m_tx_fifo_push()     Allocates append-space in the FIFO
+ *    i2400m_tx_new()           Opens a new message in the FIFO
+ *    i2400m_tx_fits()          Checks if a new payload fits in the message
+ *    i2400m_tx_close()         Closes an open message in the FIFO
+ *    i2400m_tx_skip_tail()     Marks unusable FIFO tail space
+ *    i2400m->bus_tx_kick()
+ *
+ * Now i2400m->bus_tx_kick() is the the bus-specific driver backend
+ * implementation; that would do:
+ *
+ * i2400m->bus_tx_kick()
+ *   i2400m_tx_msg_get()	Gets first message ready to go
+ *   ...sends it...
+ *   i2400m_tx_msg_sent()       Ack the message is sent; repeat from
+ *                              _tx_msg_get() until it returns NULL
+ *                               (FIFO empty).
+ */
+#include <linux/netdevice.h>
+#include "i2400m.h"
+
+
+#define D_SUBMODULE tx
+#include "debug-levels.h"
+
+enum {
+	/**
+	 * TX Buffer size
+	 *
+	 * Doc says maximum transaction is 16KiB. If we had 16KiB en
+	 * route and 16KiB being queued, it boils down to needing
+	 * 32KiB.
+	 */
+	I2400M_TX_BUF_SIZE = 32768,
+	/**
+	 * Message header and payload descriptors have to be 16
+	 * aligned (16 + 4 * N = 16 * M). If we take that average sent
+	 * packets are MTU size (~1400-~1500) it follows that we could
+	 * fit at most 10-11 payloads in one transaction. To meet the
+	 * alignment requirement, that means we need to leave space
+	 * for 12 (64 bytes). To simplify, we leave space for that. If
+	 * at the end there are less, we pad up to the nearest
+	 * multiple of 16.
+	 */
+	I2400M_TX_PLD_MAX = 12,
+	I2400M_TX_PLD_SIZE = sizeof(struct i2400m_msg_hdr)
+	+ I2400M_TX_PLD_MAX * sizeof(struct i2400m_pld),
+	I2400M_TX_SKIP = 0x80000000,
+};
+
+#define TAIL_FULL ((void *)~(unsigned long)NULL)
+
+/*
+ * Allocate @size bytes in the TX fifo, return a pointer to it
+ *
+ * @i2400m: device descriptor
+ * @size: size of the buffer we need to allocate
+ * @padding: ensure that there is at least this many bytes of free
+ *     contiguous space in the fifo. This is needed because later on
+ *     we might need to add padding.
+ *
+ * Returns:
+ *
+ *     Pointer to the allocated space. NULL if there is no
+ *     space. TAIL_FULL if there is no space at the tail but there is at
+ *     the head (Case B below).
+ *
+ * These are the two basic cases we need to keep an eye for -- it is
+ * much better explained in linux/kernel/kfifo.c, but this code
+ * basically does the same. No rocket science here.
+ *
+ *       Case A               Case B
+ * N  ___________          ___________
+ *   | tail room |        |   data    |
+ *   |           |        |           |
+ *   |<-  IN   ->|        |<-  OUT  ->|
+ *   |           |        |           |
+ *   |   data    |        |   room    |
+ *   |           |        |           |
+ *   |<-  OUT  ->|        |<-  IN   ->|
+ *   |           |        |           |
+ *   | head room |        |   data    |
+ * 0  -----------          -----------
+ *
+ * We allocate only *contiguous* space.
+ *
+ * We can allocate only from 'room'. In Case B, it is simple; in case
+ * A, we only try from the tail room; if it is not enough, we just
+ * fail and return TAIL_FULL and let the caller figure out if we wants to
+ * skip the tail room and try to allocate from the head.
+ *
+ * Note:
+ *
+ *     Assumes i2400m->tx_lock is taken, and we use that as a barrier
+ *
+ *     The indexes keep increasing and we reset them to zero when we
+ *     pop data off the queue
+ */
+static
+void *i2400m_tx_fifo_push(struct i2400m *i2400m, size_t size, size_t padding)
+{
+	struct device *dev = i2400m_dev(i2400m);
+	size_t room, tail_room, needed_size;
+	void *ptr;
+
+	needed_size = size + padding;
+	room = I2400M_TX_BUF_SIZE - (i2400m->tx_in - i2400m->tx_out);
+	if (room < needed_size)	{ /* this takes care of Case B */
+		d_printf(2, dev, "fifo push %zu/%zu: no space\n",
+			 size, padding);
+		return NULL;
+	}
+	/* Is there space at the tail? */
+	tail_room = I2400M_TX_BUF_SIZE - i2400m->tx_in % I2400M_TX_BUF_SIZE;
+	if (tail_room < needed_size) {
+		if (i2400m->tx_out % I2400M_TX_BUF_SIZE
+		    < i2400m->tx_in % I2400M_TX_BUF_SIZE) {
+			d_printf(2, dev, "fifo push %zu/%zu: tail full\n",
+				 size, padding);
+			return TAIL_FULL;	/* There might be head space */
+		} else {
+			d_printf(2, dev, "fifo push %zu/%zu: no head space\n",
+				 size, padding);
+			return NULL;	/* There is no space */
+		}
+	}
+	ptr = i2400m->tx_buf + i2400m->tx_in % I2400M_TX_BUF_SIZE;
+	d_printf(2, dev, "fifo push %zu/%zu: at @%zu\n", size, padding,
+		 i2400m->tx_in % I2400M_TX_BUF_SIZE);
+	i2400m->tx_in += size;
+	return ptr;
+}
+
+
+/*
+ * Mark the tail of the FIFO buffer as 'to-skip'
+ *
+ * We should never hit the BUG_ON() because all the sizes we push to
+ * the FIFO are padded to be a multiple of 16 -- the size of *msg
+ * (I2400M_PL_PAD for the payloads, I2400M_TX_PLD_SIZE for the
+ * header).
+ *
+ * Note:
+ *
+ *     Assumes i2400m->tx_lock is taken, and we use that as a barrier
+ */
+static
+void i2400m_tx_skip_tail(struct i2400m *i2400m)
+{
+	struct device *dev = i2400m_dev(i2400m);
+	size_t tx_in = i2400m->tx_in % I2400M_TX_BUF_SIZE;
+	size_t tail_room = I2400M_TX_BUF_SIZE - tx_in;
+	struct i2400m_msg_hdr *msg = i2400m->tx_buf + tx_in;
+	BUG_ON(tail_room < sizeof(*msg));
+	msg->size = tail_room | I2400M_TX_SKIP;
+	d_printf(2, dev, "skip tail: skipping %zu bytes @%zu\n",
+		 tail_room, tx_in);
+	i2400m->tx_in += tail_room;
+}
+
+
+/*
+ * Check if a skb will fit in the TX queue's current active TX
+ * message (if there are still descriptors left unused).
+ *
+ * Returns:
+ *     0 if the message won't fit, 1 if it will.
+ *
+ * Note:
+ *
+ *     Assumes a TX message is active (i2400m->tx_msg).
+ *
+ *     Assumes i2400m->tx_lock is taken, and we use that as a barrier
+ */
+static
+unsigned i2400m_tx_fits(struct i2400m *i2400m)
+{
+	struct i2400m_msg_hdr *msg_hdr = i2400m->tx_msg;
+	return le16_to_cpu(msg_hdr->num_pls) < I2400M_TX_PLD_MAX;
+
+}
+
+
+/*
+ * Start a new TX message header in the queue.
+ *
+ * Reserve memory from the base FIFO engine and then just initialize
+ * the message header.
+ *
+ * We allocate the biggest TX message header we might need (one that'd
+ * fit I2400M_TX_PLD_MAX payloads) -- when it is closed it will be
+ * 'ironed it out' and the unneeded parts removed.
+ *
+ * NOTE:
+ *
+ *     Assumes that the previous message is CLOSED (eg: either
+ *     there was none or 'i2400m_tx_close()' was called on it).
+ *
+ *     Assumes i2400m->tx_lock is taken, and we use that as a barrier
+ */
+static
+void i2400m_tx_new(struct i2400m *i2400m)
+{
+	struct device *dev = i2400m_dev(i2400m);
+	struct i2400m_msg_hdr *tx_msg;
+	BUG_ON(i2400m->tx_msg != NULL);
+try_head:
+	tx_msg = i2400m_tx_fifo_push(i2400m, I2400M_TX_PLD_SIZE, 0);
+	if (tx_msg == NULL)
+		goto out;
+	else if (tx_msg == TAIL_FULL) {
+		i2400m_tx_skip_tail(i2400m);
+		d_printf(2, dev, "new TX message: tail full, trying head\n");
+		goto try_head;
+	}
+	memset(tx_msg, 0, I2400M_TX_PLD_SIZE);
+	tx_msg->size = I2400M_TX_PLD_SIZE;
+out:
+	i2400m->tx_msg = tx_msg;
+	d_printf(2, dev, "new TX message: %p @%zu\n",
+		 tx_msg, (void *) tx_msg - i2400m->tx_buf);
+}
+
+
+/*
+ * Finalize the current TX message header
+ *
+ * Sets the message header to be at the proper location depending on
+ * how many descriptors we have (check documentation at the file's
+ * header for more info on that).
+ *
+ * Appends padding bytes to make sure the whole TX message (counting
+ * from the 'relocated' message header) is aligned to
+ * tx_block_size. We assume the _append() code has left enough space
+ * in the FIFO for that. If there are no payloads, just pass, as it
+ * won't be transferred.
+ *
+ * The amount of padding bytes depends on how many payloads are in the
+ * TX message, as the "msg header and payload descriptors" will be
+ * shifted up in the buffer.
+ */
+static
+void i2400m_tx_close(struct i2400m *i2400m)
+{
+	struct device *dev = i2400m_dev(i2400m);
+	struct i2400m_msg_hdr *tx_msg = i2400m->tx_msg;
+	struct i2400m_msg_hdr *tx_msg_moved;
+	size_t aligned_size, padding, hdr_size;
+	void *pad_buf;
+
+	if (tx_msg->size & I2400M_TX_SKIP)	/* a skipper? nothing to do */
+		goto out;
+
+	/* Relocate the message header
+	 *
+	 * Find the current header size, align it to 16 and if we need
+	 * to move it so the tail is next to the payloads, move it and
+	 * set the offset.
+	 *
+	 * If it moved, this header is good only for transmission; the
+	 * original one (it is kept if we moved) is still used to
+	 * figure out where the next TX message starts (and where the
+	 * offset to the moved header is).
+	 */
+	hdr_size = sizeof(*tx_msg)
+		+ le16_to_cpu(tx_msg->num_pls) * sizeof(tx_msg->pld[0]);
+	hdr_size = ALIGN(hdr_size, I2400M_PL_PAD);
+	tx_msg->offset = I2400M_TX_PLD_SIZE - hdr_size;
+	tx_msg_moved = (void *) tx_msg + tx_msg->offset;
+	memmove(tx_msg_moved, tx_msg, hdr_size);
+	tx_msg_moved->size -= tx_msg->offset;
+	/*
+	 * Now figure out how much we have to add to the (moved!)
+	 * message so the size is a multiple of i2400m->bus_tx_block_size.
+	 */
+	aligned_size = ALIGN(tx_msg_moved->size, i2400m->bus_tx_block_size);
+	padding = aligned_size - tx_msg_moved->size;
+	if (padding > 0) {
+		pad_buf = i2400m_tx_fifo_push(i2400m, padding, 0);
+		if (unlikely(WARN_ON(pad_buf == NULL
+				     || pad_buf == TAIL_FULL))) {
+			/* This should not happen -- append should verify
+			 * there is always space left at least to append
+			 * tx_block_size */
+			dev_err(dev,
+				"SW BUG! Possible data leakage from memory the "
+				"device should not read for padding - "
+				"size %lu aligned_size %zu tx_buf %p in "
+				"%zu out %zu\n",
+				(unsigned long) tx_msg_moved->size,
+				aligned_size, i2400m->tx_buf, i2400m->tx_in,
+				i2400m->tx_out);
+		} else
+			memset(pad_buf, 0xad, padding);
+	}
+	tx_msg_moved->padding = cpu_to_le16(padding);
+	tx_msg_moved->size += padding;
+	if (tx_msg != tx_msg_moved)
+		tx_msg->size += padding;
+out:
+	i2400m->tx_msg = NULL;
+}
+
+
+/**
+ * i2400m_tx - send the data in a buffer to the device
+ *
+ * @buf: pointer to the buffer to transmit
+ *
+ * @buf_len: buffer size
+ *
+ * @pl_type: type of the payload we are sending.
+ *
+ * Returns:
+ *     0 if ok, < 0 errno code on error (-ENOSPC, if there is no more
+ *     room for the message in the queue).
+ *
+ * Appends the buffer to the TX FIFO and notifies the bus-specific
+ * part of the driver that there is new data ready to transmit.
+ * Once this function returns, the buffer has been copied, so it can
+ * be reused.
+ *
+ * The steps followed to append are explained in detail in the file
+ * header.
+ *
+ * Whenever we write to a message, we increase msg->size, so it
+ * reflects exactly how big the message is. This is needed so that if
+ * we concatenate two messages before they can be sent, the code that
+ * sends the messages can find the boundaries (and it will replace the
+ * size with the real barker before sending).
+ *
+ * Note:
+ *
+ *     Cold and warm reset payloads need to be sent as a single
+ *     payload, so we handle that.
+ */
+int i2400m_tx(struct i2400m *i2400m, const void *buf, size_t buf_len,
+	      enum i2400m_pt pl_type)
+{
+	int result = -ENOSPC;
+	struct device *dev = i2400m_dev(i2400m);
+	unsigned long flags;
+	size_t padded_len;
+	void *ptr;
+	unsigned is_singleton = pl_type == I2400M_PT_RESET_WARM
+		|| pl_type == I2400M_PT_RESET_COLD;
+
+	d_fnstart(3, dev, "(i2400m %p skb %p [%zu bytes] pt %u)\n",
+		  i2400m, buf, buf_len, pl_type);
+	padded_len = ALIGN(buf_len, I2400M_PL_PAD);
+	d_printf(5, dev, "padded_len %zd buf_len %zd\n", padded_len, buf_len);
+	/* If there is no current TX message, create one; if the
+	 * current one is out of payload slots or we have a singleton,
+	 * close it and start a new one */
+	spin_lock_irqsave(&i2400m->tx_lock, flags);
+try_new:
+	if (unlikely(i2400m->tx_msg == NULL))
+		i2400m_tx_new(i2400m);
+	else if (unlikely(!i2400m_tx_fits(i2400m)
+			  || (is_singleton && i2400m->tx_msg->num_pls != 0))) {
+		d_printf(2, dev, "closing TX message (fits %u singleton "
+			 "%u num_pls %u)\n", i2400m_tx_fits(i2400m),
+			 is_singleton, i2400m->tx_msg->num_pls);
+		i2400m_tx_close(i2400m);
+		i2400m_tx_new(i2400m);
+	}
+	if (i2400m->tx_msg->size + padded_len > I2400M_TX_BUF_SIZE / 2) {
+		d_printf(2, dev, "TX: message too big, going new\n");
+		i2400m_tx_close(i2400m);
+		i2400m_tx_new(i2400m);
+	}
+	if (i2400m->tx_msg == NULL)
+		goto error_tx_new;
+	/* So we have a current message header; now append space for
+	 * the message -- if there is not enough, try the head */
+	ptr = i2400m_tx_fifo_push(i2400m, padded_len,
+				  i2400m->bus_tx_block_size);
+	if (ptr == TAIL_FULL) {	/* Tail is full, try head */
+		d_printf(2, dev, "pl append: tail full\n");
+		i2400m_tx_close(i2400m);
+		i2400m_tx_skip_tail(i2400m);
+		goto try_new;
+	} else if (ptr == NULL) {	/* All full */
+		result = -ENOSPC;
+		d_printf(2, dev, "pl append: all full\n");
+	} else {			/* Got space, copy it, set padding */
+		struct i2400m_msg_hdr *tx_msg = i2400m->tx_msg;
+		unsigned num_pls = le16_to_cpu(tx_msg->num_pls);
+		memcpy(ptr, buf, buf_len);
+		memset(ptr + buf_len, 0xad, padded_len - buf_len);
+		i2400m_pld_set(&tx_msg->pld[num_pls], buf_len, pl_type);
+		d_printf(3, dev, "pld 0x%08x (type 0x%1x len 0x%04zx\n",
+			 le32_to_cpu(tx_msg->pld[num_pls].val),
+			 pl_type, buf_len);
+		tx_msg->num_pls = le16_to_cpu(num_pls+1);
+		tx_msg->size += padded_len;
+		d_printf(2, dev, "TX: appended %zu b (up to %u b) pl #%u \n",
+			padded_len, tx_msg->size, num_pls+1);
+		d_printf(2, dev,
+			 "TX: appended hdr @%zu %zu b pl #%u @%zu %zu/%zu b\n",
+			 (void *)tx_msg - i2400m->tx_buf, (size_t)tx_msg->size,
+			 num_pls+1, ptr - i2400m->tx_buf, buf_len, padded_len);
+		result = 0;
+		if (is_singleton)
+			i2400m_tx_close(i2400m);
+	}
+error_tx_new:
+	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+	i2400m->bus_tx_kick(i2400m);	/* always kick, might free up space */
+	d_fnend(3, dev, "(i2400m %p skb %p [%zu bytes] pt %u) = %d\n",
+		i2400m, buf, buf_len, pl_type, result);
+	return result;
+}
+EXPORT_SYMBOL_GPL(i2400m_tx);
+
+
+/**
+ * i2400m_tx_msg_get - Get the first TX message in the FIFO to start sending it
+ *
+ * @i2400m: device descriptors
+ * @bus_size: where to place the size of the TX message
+ *
+ * Called by the bus-specific driver to get the first TX message at
+ * the FIF that is ready for transmission.
+ *
+ * It sets the state in @i2400m to indicate the bus-specific driver is
+ * transfering that message (i2400m->tx_msg_size).
+ *
+ * Once the transfer is completed, call i2400m_tx_msg_sent().
+ *
+ * Notes:
+ *
+ *     The size of the TX message to be transmitted might be smaller than
+ *     that of the TX message in the FIFO (in case the header was
+ *     shorter). Hence, we copy it in @bus_size, for the bus layer to
+ *     use. We keep the message's size in i2400m->tx_msg_size so that
+ *     when the bus later is done transferring we know how much to
+ *     advance the fifo.
+ *
+ *     We collect statistics here as all the data is available and we
+ *     assume it is going to work [see i2400m_tx_msg_sent()].
+ */
+struct i2400m_msg_hdr *i2400m_tx_msg_get(struct i2400m *i2400m,
+					 size_t *bus_size)
+{
+	struct device *dev = i2400m_dev(i2400m);
+	struct i2400m_msg_hdr *tx_msg, *tx_msg_moved;
+	unsigned long flags, pls;
+
+	d_fnstart(3, dev, "(i2400m %p bus_size %p)\n", i2400m, bus_size);
+	spin_lock_irqsave(&i2400m->tx_lock, flags);
+skip:
+	tx_msg_moved = NULL;
+	if (i2400m->tx_in == i2400m->tx_out) {	/* Empty FIFO? */
+		i2400m->tx_in = 0;
+		i2400m->tx_out = 0;
+		d_printf(2, dev, "TX: FIFO empty: resetting\n");
+		goto out_unlock;
+	}
+	tx_msg = i2400m->tx_buf + i2400m->tx_out % I2400M_TX_BUF_SIZE;
+	if (tx_msg->size & I2400M_TX_SKIP) {	/* skip? */
+		d_printf(2, dev, "TX: skip: msg @%zu (%zu b)\n",
+			 i2400m->tx_out % I2400M_TX_BUF_SIZE,
+			 (size_t) tx_msg->size & ~I2400M_TX_SKIP);
+		i2400m->tx_out += tx_msg->size & ~I2400M_TX_SKIP;
+		goto skip;
+	}
+
+	if (tx_msg->num_pls == 0) {		/* No payloads? */
+		if (tx_msg == i2400m->tx_msg) {	/* open, we are done */
+			d_printf(2, dev,
+				 "TX: FIFO empty: open msg w/o payloads @%zu\n",
+				 (void *) tx_msg - i2400m->tx_buf);
+			tx_msg = NULL;
+			goto out_unlock;
+		} else {			/* closed, skip it */
+			d_printf(2, dev,
+				 "TX: skip msg w/o payloads @%zu (%zu b)\n",
+				 (void *) tx_msg - i2400m->tx_buf,
+				 (size_t) tx_msg->size);
+			i2400m->tx_out += tx_msg->size & ~I2400M_TX_SKIP;
+			goto skip;
+		}
+	}
+	if (tx_msg == i2400m->tx_msg)		/* open msg? */
+		i2400m_tx_close(i2400m);
+
+	/* Now we have a valid TX message (with payloads) to TX */
+	tx_msg_moved = (void *) tx_msg + tx_msg->offset;
+	i2400m->tx_msg_size = tx_msg->size;
+	*bus_size = tx_msg_moved->size;
+	d_printf(2, dev, "TX: pid %d msg hdr at @%zu offset +@%zu "
+		 "size %zu bus_size %zu\n",
+		 current->pid, (void *) tx_msg - i2400m->tx_buf,
+		 (size_t) tx_msg->offset, (size_t) tx_msg->size,
+		 (size_t) tx_msg_moved->size);
+	tx_msg_moved->barker = le32_to_cpu(I2400M_H2D_PREVIEW_BARKER);
+	tx_msg_moved->sequence = le32_to_cpu(i2400m->tx_sequence++);
+
+	pls = le32_to_cpu(tx_msg_moved->num_pls);
+	i2400m->tx_pl_num += pls;		/* Update stats */
+	if (pls > i2400m->tx_pl_max)
+		i2400m->tx_pl_max = pls;
+	if (pls < i2400m->tx_pl_min)
+		i2400m->tx_pl_min = pls;
+	i2400m->tx_num++;
+	i2400m->tx_size_acc += *bus_size;
+	if (*bus_size < i2400m->tx_size_min)
+		i2400m->tx_size_min = *bus_size;
+	if (*bus_size > i2400m->tx_size_max)
+		i2400m->tx_size_max = *bus_size;
+out_unlock:
+	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+	d_fnstart(3, dev, "(i2400m %p bus_size %p [%zu]) = %p\n",
+		  i2400m, bus_size, *bus_size, tx_msg_moved);
+	return tx_msg_moved;
+}
+EXPORT_SYMBOL_GPL(i2400m_tx_msg_get);
+
+
+/**
+ * i2400m_tx_msg_sent - indicate the transmission of a TX message
+ *
+ * @i2400m: device descriptor
+ *
+ * Called by the bus-specific driver when a message has been sent;
+ * this pops it from the FIFO; and as there is space, start the queue
+ * in case it was stopped.
+ *
+ * Should be called even if the message send failed and we are
+ * dropping this TX message.
+ */
+void i2400m_tx_msg_sent(struct i2400m *i2400m)
+{
+	unsigned n;
+	unsigned long flags;
+	struct device *dev = i2400m_dev(i2400m);
+
+	d_fnstart(3, dev, "(i2400m %p)\n", i2400m);
+	spin_lock_irqsave(&i2400m->tx_lock, flags);
+	i2400m->tx_out += i2400m->tx_msg_size;
+	d_printf(2, dev, "TX: sent %zu b\n", (size_t) i2400m->tx_msg_size);
+	i2400m->tx_msg_size = 0;
+	BUG_ON(i2400m->tx_out > i2400m->tx_in);
+	/* level them FIFO markers off */
+	n = i2400m->tx_out / I2400M_TX_BUF_SIZE;
+	i2400m->tx_out %= I2400M_TX_BUF_SIZE;
+	i2400m->tx_in -= n * I2400M_TX_BUF_SIZE;
+	netif_start_queue(i2400m->wimax_dev.net_dev);
+	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+	d_fnend(3, dev, "(i2400m %p) = void\n", i2400m);
+}
+EXPORT_SYMBOL_GPL(i2400m_tx_msg_sent);
+
+
+/**
+ * i2400m_tx_setup - Initialize the TX queue and infrastructure
+ *
+ * Make sure we reset the TX sequence to zero, as when this function
+ * is called, the firmware has been just restarted.
+ */
+int i2400m_tx_setup(struct i2400m *i2400m)
+{
+	int result;
+
+	/* Do this here only once -- can't do on
+	 * i2400m_hard_start_xmit() as we'll cause race conditions if
+	 * the WS was scheduled on another CPU */
+	INIT_WORK(&i2400m->wake_tx_ws, i2400m_wake_tx_work);
+
+	i2400m->tx_sequence = 0;
+	i2400m->tx_buf = kmalloc(I2400M_TX_BUF_SIZE, GFP_KERNEL);
+	if (i2400m->tx_buf == NULL)
+		result = -ENOMEM;
+	else
+		result = 0;
+	/* Huh? the bus layer has to define this... */
+	BUG_ON(i2400m->bus_tx_block_size == 0);
+	return result;
+
+}
+
+
+/**
+ * i2400m_tx_release - Tear down the TX queue and infrastructure
+ */
+void i2400m_tx_release(struct i2400m *i2400m)
+{
+	kfree(i2400m->tx_buf);
+}