qib_user_sdma.c

/*
 * Copyright (c) 2007, 2008, 2009 QLogic Corporation. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     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.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
#include <linux/mm.h>
#include <linux/types.h>
#include <linux/device.h>
#include <linux/dmapool.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/highmem.h>
#include <linux/io.h>
#include <linux/uio.h>
#include <linux/rbtree.h>
#include <linux/spinlock.h>
#include <linux/delay.h>

#include "qib.h"
#include "qib_user_sdma.h"

/* minimum size of header */
#define QIB_USER_SDMA_MIN_HEADER_LENGTH 64
/* expected size of headers (for dma_pool) */
#define QIB_USER_SDMA_EXP_HEADER_LENGTH 64
/* attempt to drain the queue for 5secs */
#define QIB_USER_SDMA_DRAIN_TIMEOUT 500

struct qib_user_sdma_pkt {
	u8 naddr;               /* dimension of addr (1..3) ... */
	u32 counter;            /* sdma pkts queued counter for this entry */
	u64 added;              /* global descq number of entries */

	struct {
		u32 offset;                     /* offset for kvaddr, addr */
		u32 length;                     /* length in page */
		u8  put_page;                   /* should we put_page? */
		u8  dma_mapped;                 /* is page dma_mapped? */
		struct page *page;              /* may be NULL (coherent mem) */
		void *kvaddr;                   /* FIXME: only for pio hack */
		dma_addr_t addr;
	} addr[4];   /* max pages, any more and we coalesce */
	struct list_head list;  /* list element */
};

struct qib_user_sdma_queue {
	/*
	 * pkts sent to dma engine are queued on this
	 * list head.  the type of the elements of this
	 * list are struct qib_user_sdma_pkt...
	 */
	struct list_head sent;

	/* headers with expected length are allocated from here... */
	char header_cache_name[64];
	struct dma_pool *header_cache;

	/* packets are allocated from the slab cache... */
	char pkt_slab_name[64];
	struct kmem_cache *pkt_slab;

	/* as packets go on the queued queue, they are counted... */
	u32 counter;
	u32 sent_counter;

	/* dma page table */
	struct rb_root dma_pages_root;

	/* protect everything above... */
	struct mutex lock;
};

struct qib_user_sdma_queue *
qib_user_sdma_queue_create(struct device *dev, int unit, int ctxt, int sctxt)
{
	struct qib_user_sdma_queue *pq =
		kmalloc(sizeof(struct qib_user_sdma_queue), GFP_KERNEL);

	if (!pq)
		goto done;

	pq->counter = 0;
	pq->sent_counter = 0;
	INIT_LIST_HEAD(&pq->sent);

	mutex_init(&pq->lock);

	snprintf(pq->pkt_slab_name, sizeof(pq->pkt_slab_name),
		 "qib-user-sdma-pkts-%u-%02u.%02u", unit, ctxt, sctxt);
	pq->pkt_slab = kmem_cache_create(pq->pkt_slab_name,
					 sizeof(struct qib_user_sdma_pkt),
					 0, 0, NULL);

	if (!pq->pkt_slab)
		goto err_kfree;

	snprintf(pq->header_cache_name, sizeof(pq->header_cache_name),
		 "qib-user-sdma-headers-%u-%02u.%02u", unit, ctxt, sctxt);
	pq->header_cache = dma_pool_create(pq->header_cache_name,
					   dev,
					   QIB_USER_SDMA_EXP_HEADER_LENGTH,
					   4, 0);
	if (!pq->header_cache)
		goto err_slab;

	pq->dma_pages_root = RB_ROOT;

	goto done;

err_slab:
	kmem_cache_destroy(pq->pkt_slab);
err_kfree:
	kfree(pq);
	pq = NULL;

done:
	return pq;
}

static void qib_user_sdma_init_frag(struct qib_user_sdma_pkt *pkt,
				    int i, size_t offset, size_t len,
				    int put_page, int dma_mapped,
				    struct page *page,
				    void *kvaddr, dma_addr_t dma_addr)
{
	pkt->addr[i].offset = offset;
	pkt->addr[i].length = len;
	pkt->addr[i].put_page = put_page;
	pkt->addr[i].dma_mapped = dma_mapped;
	pkt->addr[i].page = page;
	pkt->addr[i].kvaddr = kvaddr;
	pkt->addr[i].addr = dma_addr;
}

static void qib_user_sdma_init_header(struct qib_user_sdma_pkt *pkt,
				      u32 counter, size_t offset,
				      size_t len, int dma_mapped,
				      struct page *page,
				      void *kvaddr, dma_addr_t dma_addr)
{
	pkt->naddr = 1;
	pkt->counter = counter;
	qib_user_sdma_init_frag(pkt, 0, offset, len, 0, dma_mapped, page,
				kvaddr, dma_addr);
}

/* we've too many pages in the iovec, coalesce to a single page */
static int qib_user_sdma_coalesce(const struct qib_devdata *dd,
				  struct qib_user_sdma_pkt *pkt,
				  const struct iovec *iov,
				  unsigned long niov)
{
	int ret = 0;
	struct page *page = alloc_page(GFP_KERNEL);
	void *mpage_save;
	char *mpage;
	int i;
	int len = 0;
	dma_addr_t dma_addr;

	if (!page) {
		ret = -ENOMEM;
		goto done;
	}

	mpage = kmap(page);
	mpage_save = mpage;
	for (i = 0; i < niov; i++) {
		int cfur;

		cfur = copy_from_user(mpage,
				      iov[i].iov_base, iov[i].iov_len);
		if (cfur) {
			ret = -EFAULT;
			goto free_unmap;
		}

		mpage += iov[i].iov_len;
		len += iov[i].iov_len;
	}

	dma_addr = dma_map_page(&dd->pcidev->dev, page, 0, len,
				DMA_TO_DEVICE);
	if (dma_mapping_error(&dd->pcidev->dev, dma_addr)) {
		ret = -ENOMEM;
		goto free_unmap;
	}

	qib_user_sdma_init_frag(pkt, 1, 0, len, 0, 1, page, mpage_save,
				dma_addr);
	pkt->naddr = 2;

	goto done;

free_unmap:
	kunmap(page);
	__free_page(page);
done:
	return ret;
}

/*
 * How many pages in this iovec element?
 */
static int qib_user_sdma_num_pages(const struct iovec *iov)
{
	const unsigned long addr  = (unsigned long) iov->iov_base;
	const unsigned long  len  = iov->iov_len;
	const unsigned long spage = addr & PAGE_MASK;
	const unsigned long epage = (addr + len - 1) & PAGE_MASK;

	return 1 + ((epage - spage) >> PAGE_SHIFT);
}

/*
 * Truncate length to page boundary.
 */
static int qib_user_sdma_page_length(unsigned long addr, unsigned long len)
{
	const unsigned long offset = addr & ~PAGE_MASK;

	return ((offset + len) > PAGE_SIZE) ? (PAGE_SIZE - offset) : len;
}

static void qib_user_sdma_free_pkt_frag(struct device *dev,
					struct qib_user_sdma_queue *pq,
					struct qib_user_sdma_pkt *pkt,
					int frag)
{
	const int i = frag;

	if (pkt->addr[i].page) {
		if (pkt->addr[i].dma_mapped)
			dma_unmap_page(dev,
				       pkt->addr[i].addr,
				       pkt->addr[i].length,
				       DMA_TO_DEVICE);

		if (pkt->addr[i].kvaddr)
			kunmap(pkt->addr[i].page);

		if (pkt->addr[i].put_page)
			put_page(pkt->addr[i].page);
		else
			__free_page(pkt->addr[i].page);
	} else if (pkt->addr[i].kvaddr)
		/* free coherent mem from cache... */
		dma_pool_free(pq->header_cache,
			      pkt->addr[i].kvaddr, pkt->addr[i].addr);
}

/* return number of pages pinned... */
static int qib_user_sdma_pin_pages(const struct qib_devdata *dd,
				   struct qib_user_sdma_pkt *pkt,
				   unsigned long addr, int tlen, int npages)
{
	struct page *pages[2];
	int j;
	int ret;

	ret = get_user_pages(current, current->mm, addr,
			     npages, 0, 1, pages, NULL);

	if (ret != npages) {
		int i;

		for (i = 0; i < ret; i++)
			put_page(pages[i]);

		ret = -ENOMEM;
		goto done;
	}

	for (j = 0; j < npages; j++) {
		/* map the pages... */
		const int flen = qib_user_sdma_page_length(addr, tlen);
		dma_addr_t dma_addr =
			dma_map_page(&dd->pcidev->dev,
				     pages[j], 0, flen, DMA_TO_DEVICE);
		unsigned long fofs = addr & ~PAGE_MASK;

		if (dma_mapping_error(&dd->pcidev->dev, dma_addr)) {
			ret = -ENOMEM;
			goto done;
		}

		qib_user_sdma_init_frag(pkt, pkt->naddr, fofs, flen, 1, 1,
					pages[j], kmap(pages[j]), dma_addr);

		pkt->naddr++;
		addr += flen;
		tlen -= flen;
	}

done:
	return ret;
}

static int qib_user_sdma_pin_pkt(const struct qib_devdata *dd,
				 struct qib_user_sdma_queue *pq,
				 struct qib_user_sdma_pkt *pkt,
				 const struct iovec *iov,
				 unsigned long niov)
{
	int ret = 0;
	unsigned long idx;

	for (idx = 0; idx < niov; idx++) {
		const int npages = qib_user_sdma_num_pages(iov + idx);
		const unsigned long addr = (unsigned long) iov[idx].iov_base;

		ret = qib_user_sdma_pin_pages(dd, pkt, addr,
					      iov[idx].iov_len, npages);
		if (ret < 0)
			goto free_pkt;
	}

	goto done;

free_pkt:
	for (idx = 0; idx < pkt->naddr; idx++)
		qib_user_sdma_free_pkt_frag(&dd->pcidev->dev, pq, pkt, idx);

done:
	return ret;
}

static int qib_user_sdma_init_payload(const struct qib_devdata *dd,
				      struct qib_user_sdma_queue *pq,
				      struct qib_user_sdma_pkt *pkt,
				      const struct iovec *iov,
				      unsigned long niov, int npages)
{
	int ret = 0;

	if (npages >= ARRAY_SIZE(pkt->addr))
		ret = qib_user_sdma_coalesce(dd, pkt, iov, niov);
	else
		ret = qib_user_sdma_pin_pkt(dd, pq, pkt, iov, niov);

	return ret;
}

/* free a packet list -- return counter value of last packet */
static void qib_user_sdma_free_pkt_list(struct device *dev,
					struct qib_user_sdma_queue *pq,
					struct list_head *list)
{
	struct qib_user_sdma_pkt *pkt, *pkt_next;

	list_for_each_entry_safe(pkt, pkt_next, list, list) {
		int i;

		for (i = 0; i < pkt->naddr; i++)
			qib_user_sdma_free_pkt_frag(dev, pq, pkt, i);

		kmem_cache_free(pq->pkt_slab, pkt);
	}
	INIT_LIST_HEAD(list);
}

/*
 * copy headers, coalesce etc -- pq->lock must be held
 *
 * we queue all the packets to list, returning the
 * number of bytes total.  list must be empty initially,
 * as, if there is an error we clean it...
 */
static int qib_user_sdma_queue_pkts(const struct qib_devdata *dd,
				    struct qib_user_sdma_queue *pq,
				    struct list_head *list,
				    const struct iovec *iov,
				    unsigned long niov,
				    int maxpkts)
{
	unsigned long idx = 0;
	int ret = 0;
	int npkts = 0;
	struct page *page = NULL;
	__le32 *pbc;
	dma_addr_t dma_addr;
	struct qib_user_sdma_pkt *pkt = NULL;
	size_t len;
	size_t nw;
	u32 counter = pq->counter;
	int dma_mapped = 0;

	while (idx < niov && npkts < maxpkts) {
		const unsigned long addr = (unsigned long) iov[idx].iov_base;
		const unsigned long idx_save = idx;
		unsigned pktnw;
		unsigned pktnwc;
		int nfrags = 0;
		int npages = 0;
		int cfur;

		dma_mapped = 0;
		len = iov[idx].iov_len;
		nw = len >> 2;
		page = NULL;

		pkt = kmem_cache_alloc(pq->pkt_slab, GFP_KERNEL);
		if (!pkt) {
			ret = -ENOMEM;
			goto free_list;
		}

		if (len < QIB_USER_SDMA_MIN_HEADER_LENGTH ||
		    len > PAGE_SIZE || len & 3 || addr & 3) {
			ret = -EINVAL;
			goto free_pkt;
		}

		if (len == QIB_USER_SDMA_EXP_HEADER_LENGTH)
			pbc = dma_pool_alloc(pq->header_cache, GFP_KERNEL,
					     &dma_addr);
		else
			pbc = NULL;

		if (!pbc) {
			page = alloc_page(GFP_KERNEL);
			if (!page) {
				ret = -ENOMEM;
				goto free_pkt;
			}
			pbc = kmap(page);
		}

		cfur = copy_from_user(pbc, iov[idx].iov_base, len);
		if (cfur) {
			ret = -EFAULT;
			goto free_pbc;
		}

		/*
		 * This assignment is a bit strange.  it's because the
		 * the pbc counts the number of 32 bit words in the full
		 * packet _except_ the first word of the pbc itself...
		 */
		pktnwc = nw - 1;

		/*
		 * pktnw computation yields the number of 32 bit words
		 * that the caller has indicated in the PBC.  note that
		 * this is one less than the total number of words that
		 * goes to the send DMA engine as the first 32 bit word
		 * of the PBC itself is not counted.  Armed with this count,
		 * we can verify that the packet is consistent with the
		 * iovec lengths.
		 */
		pktnw = le32_to_cpu(*pbc) & QIB_PBC_LENGTH_MASK;
		if (pktnw < pktnwc || pktnw > pktnwc + (PAGE_SIZE >> 2)) {
			ret = -EINVAL;
			goto free_pbc;
		}

		idx++;
		while (pktnwc < pktnw && idx < niov) {
			const size_t slen = iov[idx].iov_len;
			const unsigned long faddr =
				(unsigned long) iov[idx].iov_base;

			if (slen & 3 || faddr & 3 || !slen ||
			    slen > PAGE_SIZE) {
				ret = -EINVAL;
				goto free_pbc;
			}

			npages++;
			if ((faddr & PAGE_MASK) !=
			    ((faddr + slen - 1) & PAGE_MASK))
				npages++;

			pktnwc += slen >> 2;
			idx++;
			nfrags++;
		}

		if (pktnwc != pktnw) {
			ret = -EINVAL;
			goto free_pbc;
		}

		if (page) {
			dma_addr = dma_map_page(&dd->pcidev->dev,
						page, 0, len, DMA_TO_DEVICE);
			if (dma_mapping_error(&dd->pcidev->dev, dma_addr)) {
				ret = -ENOMEM;
				goto free_pbc;
			}

			dma_mapped = 1;
		}

		qib_user_sdma_init_header(pkt, counter, 0, len, dma_mapped,
					  page, pbc, dma_addr);

		if (nfrags) {
			ret = qib_user_sdma_init_payload(dd, pq, pkt,
							 iov + idx_save + 1,
							 nfrags, npages);
			if (ret < 0)
				goto free_pbc_dma;
		}

		counter++;
		npkts++;

		list_add_tail(&pkt->list, list);
	}

	ret = idx;
	goto done;

free_pbc_dma:
	if (dma_mapped)
		dma_unmap_page(&dd->pcidev->dev, dma_addr, len, DMA_TO_DEVICE);
free_pbc:
	if (page) {
		kunmap(page);
		__free_page(page);
	} else
		dma_pool_free(pq->header_cache, pbc, dma_addr);
free_pkt:
	kmem_cache_free(pq->pkt_slab, pkt);
free_list:
	qib_user_sdma_free_pkt_list(&dd->pcidev->dev, pq, list);
done:
	return ret;
}

static void qib_user_sdma_set_complete_counter(struct qib_user_sdma_queue *pq,
					       u32 c)
{
	pq->sent_counter = c;
}

/* try to clean out queue -- needs pq->lock */
static int qib_user_sdma_queue_clean(struct qib_pportdata *ppd,
				     struct qib_user_sdma_queue *pq)
{
	struct qib_devdata *dd = ppd->dd;
	struct list_head free_list;
	struct qib_user_sdma_pkt *pkt;
	struct qib_user_sdma_pkt *pkt_prev;
	int ret = 0;

	INIT_LIST_HEAD(&free_list);

	list_for_each_entry_safe(pkt, pkt_prev, &pq->sent, list) {
		s64 descd = ppd->sdma_descq_removed - pkt->added;

		if (descd < 0)
			break;

		list_move_tail(&pkt->list, &free_list);

		/* one more packet cleaned */
		ret++;
	}

	if (!list_empty(&free_list)) {
		u32 counter;

		pkt = list_entry(free_list.prev,
				 struct qib_user_sdma_pkt, list);
		counter = pkt->counter;

		qib_user_sdma_free_pkt_list(&dd->pcidev->dev, pq, &free_list);
		qib_user_sdma_set_complete_counter(pq, counter);
	}

	return ret;
}

void qib_user_sdma_queue_destroy(struct qib_user_sdma_queue *pq)
{
	if (!pq)
		return;

	kmem_cache_destroy(pq->pkt_slab);
	dma_pool_destroy(pq->header_cache);
	kfree(pq);
}

/* clean descriptor queue, returns > 0 if some elements cleaned */
static int qib_user_sdma_hwqueue_clean(struct qib_pportdata *ppd)
{
	int ret;
	unsigned long flags;

	spin_lock_irqsave(&ppd->sdma_lock, flags);
	ret = qib_sdma_make_progress(ppd);
	spin_unlock_irqrestore(&ppd->sdma_lock, flags);

	return ret;
}

/* we're in close, drain packets so that we can cleanup successfully... */
void qib_user_sdma_queue_drain(struct qib_pportdata *ppd,
			       struct qib_user_sdma_queue *pq)
{
	struct qib_devdata *dd = ppd->dd;
	int i;

	if (!pq)
		return;

	for (i = 0; i < QIB_USER_SDMA_DRAIN_TIMEOUT; i++) {
		mutex_lock(&pq->lock);
		if (list_empty(&pq->sent)) {
			mutex_unlock(&pq->lock);
			break;
		}
		qib_user_sdma_hwqueue_clean(ppd);
		qib_user_sdma_queue_clean(ppd, pq);
		mutex_unlock(&pq->lock);
		msleep(10);
	}

	if (!list_empty(&pq->sent)) {
		struct list_head free_list;

		qib_dev_err(dd, "user sdma lists not empty: forcing!\n");
		INIT_LIST_HEAD(&free_list);
		mutex_lock(&pq->lock);
		list_splice_init(&pq->sent, &free_list);
		qib_user_sdma_free_pkt_list(&dd->pcidev->dev, pq, &free_list);
		mutex_unlock(&pq->lock);
	}
}

static inline __le64 qib_sdma_make_desc0(struct qib_pportdata *ppd,
					 u64 addr, u64 dwlen, u64 dwoffset)
{
	u8 tmpgen;

	tmpgen = ppd->sdma_generation;

	return cpu_to_le64(/* SDmaPhyAddr[31:0] */
			   ((addr & 0xfffffffcULL) << 32) |
			   /* SDmaGeneration[1:0] */
			   ((tmpgen & 3ULL) << 30) |
			   /* SDmaDwordCount[10:0] */
			   ((dwlen & 0x7ffULL) << 16) |
			   /* SDmaBufOffset[12:2] */
			   (dwoffset & 0x7ffULL));
}

static inline __le64 qib_sdma_make_first_desc0(__le64 descq)
{
	return descq | cpu_to_le64(1ULL << 12);
}

static inline __le64 qib_sdma_make_last_desc0(__le64 descq)
{
					      /* last */  /* dma head */
	return descq | cpu_to_le64(1ULL << 11 | 1ULL << 13);
}

static inline __le64 qib_sdma_make_desc1(u64 addr)
{
	/* SDmaPhyAddr[47:32] */
	return cpu_to_le64(addr >> 32);
}

static void qib_user_sdma_send_frag(struct qib_pportdata *ppd,
				    struct qib_user_sdma_pkt *pkt, int idx,
				    unsigned ofs, u16 tail)
{
	const u64 addr = (u64) pkt->addr[idx].addr +
		(u64) pkt->addr[idx].offset;
	const u64 dwlen = (u64) pkt->addr[idx].length / 4;
	__le64 *descqp;
	__le64 descq0;

	descqp = &ppd->sdma_descq[tail].qw[0];

	descq0 = qib_sdma_make_desc0(ppd, addr, dwlen, ofs);
	if (idx == 0)
		descq0 = qib_sdma_make_first_desc0(descq0);
	if (idx == pkt->naddr - 1)
		descq0 = qib_sdma_make_last_desc0(descq0);

	descqp[0] = descq0;
	descqp[1] = qib_sdma_make_desc1(addr);
}

/* pq->lock must be held, get packets on the wire... */
static int qib_user_sdma_push_pkts(struct qib_pportdata *ppd,
				   struct qib_user_sdma_queue *pq,
				   struct list_head *pktlist)
{
	struct qib_devdata *dd = ppd->dd;
	int ret = 0;
	unsigned long flags;
	u16 tail;
	u8 generation;
	u64 descq_added;

	if (list_empty(pktlist))
		return 0;

	if (unlikely(!(ppd->lflags & QIBL_LINKACTIVE)))
		return -ECOMM;

	spin_lock_irqsave(&ppd->sdma_lock, flags);

	/* keep a copy for restoring purposes in case of problems */
	generation = ppd->sdma_generation;
	descq_added = ppd->sdma_descq_added;

	if (unlikely(!__qib_sdma_running(ppd))) {
		ret = -ECOMM;
		goto unlock;
	}

	tail = ppd->sdma_descq_tail;
	while (!list_empty(pktlist)) {
		struct qib_user_sdma_pkt *pkt =
			list_entry(pktlist->next, struct qib_user_sdma_pkt,
				   list);
		int i;
		unsigned ofs = 0;
		u16 dtail = tail;

		if (pkt->naddr > qib_sdma_descq_freecnt(ppd))
			goto unlock_check_tail;

		for (i = 0; i < pkt->naddr; i++) {
			qib_user_sdma_send_frag(ppd, pkt, i, ofs, tail);
			ofs += pkt->addr[i].length >> 2;

			if (++tail == ppd->sdma_descq_cnt) {
				tail = 0;
				++ppd->sdma_generation;
			}
		}

		if ((ofs << 2) > ppd->ibmaxlen) {
			ret = -EMSGSIZE;
			goto unlock;
		}

		/*
		 * If the packet is >= 2KB mtu equivalent, we have to use
		 * the large buffers, and have to mark each descriptor as
		 * part of a large buffer packet.
		 */
		if (ofs > dd->piosize2kmax_dwords) {
			for (i = 0; i < pkt->naddr; i++) {
				ppd->sdma_descq[dtail].qw[0] |=
					cpu_to_le64(1ULL << 14);
				if (++dtail == ppd->sdma_descq_cnt)
					dtail = 0;
			}
		}

		ppd->sdma_descq_added += pkt->naddr;
		pkt->added = ppd->sdma_descq_added;
		list_move_tail(&pkt->list, &pq->sent);
		ret++;
	}

unlock_check_tail:
	/* advance the tail on the chip if necessary */
	if (ppd->sdma_descq_tail != tail)
		dd->f_sdma_update_tail(ppd, tail);

unlock:
	if (unlikely(ret < 0)) {
		ppd->sdma_generation = generation;
		ppd->sdma_descq_added = descq_added;
	}
	spin_unlock_irqrestore(&ppd->sdma_lock, flags);

	return ret;
}

int qib_user_sdma_writev(struct qib_ctxtdata *rcd,
			 struct qib_user_sdma_queue *pq,
			 const struct iovec *iov,
			 unsigned long dim)
{
	struct qib_devdata *dd = rcd->dd;
	struct qib_pportdata *ppd = rcd->ppd;
	int ret = 0;
	struct list_head list;
	int npkts = 0;

	INIT_LIST_HEAD(&list);

	mutex_lock(&pq->lock);

	/* why not -ECOMM like qib_user_sdma_push_pkts() below? */
	if (!qib_sdma_running(ppd))
		goto done_unlock;

	if (ppd->sdma_descq_added != ppd->sdma_descq_removed) {
		qib_user_sdma_hwqueue_clean(ppd);
		qib_user_sdma_queue_clean(ppd, pq);
	}

	while (dim) {
		const int mxp = 8;

		down_write(&current->mm->mmap_sem);
		ret = qib_user_sdma_queue_pkts(dd, pq, &list, iov, dim, mxp);
		up_write(&current->mm->mmap_sem);

		if (ret <= 0)
			goto done_unlock;
		else {
			dim -= ret;
			iov += ret;
		}

		/* force packets onto the sdma hw queue... */
		if (!list_empty(&list)) {
			/*
			 * Lazily clean hw queue.  the 4 is a guess of about
			 * how many sdma descriptors a packet will take (it
			 * doesn't have to be perfect).
			 */
			if (qib_sdma_descq_freecnt(ppd) < ret * 4) {
				qib_user_sdma_hwqueue_clean(ppd);
				qib_user_sdma_queue_clean(ppd, pq);
			}

			ret = qib_user_sdma_push_pkts(ppd, pq, &list);
			if (ret < 0)
				goto done_unlock;
			else {
				npkts += ret;
				pq->counter += ret;

				if (!list_empty(&list))
					goto done_unlock;
			}
		}
	}

done_unlock:
	if (!list_empty(&list))
		qib_user_sdma_free_pkt_list(&dd->pcidev->dev, pq, &list);
	mutex_unlock(&pq->lock);

	return (ret < 0) ? ret : npkts;
}

int qib_user_sdma_make_progress(struct qib_pportdata *ppd,
				struct qib_user_sdma_queue *pq)
{
	int ret = 0;

	mutex_lock(&pq->lock);
	qib_user_sdma_hwqueue_clean(ppd);
	ret = qib_user_sdma_queue_clean(ppd, pq);
	mutex_unlock(&pq->lock);

	return ret;
}

u32 qib_user_sdma_complete_counter(const struct qib_user_sdma_queue *pq)
{
	return pq ? pq->sent_counter : 0;
}

u32 qib_user_sdma_inflight_counter(struct qib_user_sdma_queue *pq)
{
	return pq ? pq->counter : 0;
}