Re: [PATCH 09/15] NTB: Use DMA Engine to Transmit and Receive

Jon Mason
2013-08-19T20:37:47Z

On Mon, Aug 19, 2013 at 03:01:54AM -0700, Dan Williams wrote:
> On Fri, Aug 2, 2013 at 10:35 AM, Jon Mason <jon.mason@intel.com> wrote:
> > Allocate and use a DMA engine channel to transmit and receive data over
> > NTB. If none is allocated, fall back to using the CPU to transfer data.
> >
> > Cc: Dan Williams <djbw@fb.com>
> > Cc: Vinod Koul <vinod.koul@intel.com>
> > Cc: Dave Jiang <dave.jiang@intel.com>
> > Signed-off-by: Jon Mason <jon.mason@intel.com>
> > ---
> > drivers/ntb/ntb_hw.c | 17 +++
> > drivers/ntb/ntb_hw.h | 1 +
> > drivers/ntb/ntb_transport.c | 285 ++++++++++++++++++++++++++++++++++++-------
> > 3 files changed, 258 insertions(+), 45 deletions(-)
> >
> > diff --git a/drivers/ntb/ntb_hw.c b/drivers/ntb/ntb_hw.c
> > index 1d8e551..014222c 100644
> > --- a/drivers/ntb/ntb_hw.c
> > +++ b/drivers/ntb/ntb_hw.c
> > @@ -350,6 +350,23 @@ int ntb_read_remote_spad(struct ntb_device *ndev, unsigned int idx, u32 *val)
> > }
> >
> > /**
> > + * ntb_get_mw_base() - get addr for the NTB memory window
> > + * @ndev: pointer to ntb_device instance
> > + * @mw: memory window number
> > + *
> > + * This function provides the base address of the memory window specified.
> > + *
> > + * RETURNS: address, or NULL on error.
> > + */
> > +resource_size_t ntb_get_mw_base(struct ntb_device *ndev, unsigned int mw)
> > +{
> > + if (mw >= ntb_max_mw(ndev))
> > + return 0;
> > +
> > + return pci_resource_start(ndev->pdev, MW_TO_BAR(mw));
> > +}
> > +
> > +/**
> > * ntb_get_mw_vbase() - get virtual addr for the NTB memory window
> > * @ndev: pointer to ntb_device instance
> > * @mw: memory window number
> > diff --git a/drivers/ntb/ntb_hw.h b/drivers/ntb/ntb_hw.h
> > index b03de80..ab5f768 100644
> > --- a/drivers/ntb/ntb_hw.h
> > +++ b/drivers/ntb/ntb_hw.h
> > @@ -240,6 +240,7 @@ int ntb_write_local_spad(struct ntb_device *ndev, unsigned int idx, u32 val);
> > int ntb_read_local_spad(struct ntb_device *ndev, unsigned int idx, u32 *val);
> > int ntb_write_remote_spad(struct ntb_device *ndev, unsigned int idx, u32 val);
> > int ntb_read_remote_spad(struct ntb_device *ndev, unsigned int idx, u32 *val);
> > +resource_size_t ntb_get_mw_base(struct ntb_device *ndev, unsigned int mw);
> > void __iomem *ntb_get_mw_vbase(struct ntb_device *ndev, unsigned int mw);
> > u64 ntb_get_mw_size(struct ntb_device *ndev, unsigned int mw);
> > void ntb_ring_sdb(struct ntb_device *ndev, unsigned int idx);
> > diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> > index f7380e9..73a35e4 100644
> > --- a/drivers/ntb/ntb_transport.c
> > +++ b/drivers/ntb/ntb_transport.c
> > @@ -47,6 +47,7 @@
> > */
> > #include <linux/debugfs.h>
> > #include <linux/delay.h>
> > +#include <linux/dmaengine.h>
> > #include <linux/dma-mapping.h>
> > #include <linux/errno.h>
> > #include <linux/export.h>
> > @@ -68,6 +69,10 @@ static unsigned char max_num_clients;
> > module_param(max_num_clients, byte, 0644);
> > MODULE_PARM_DESC(max_num_clients, "Maximum number of NTB transport clients");
> >
> > +static unsigned int copy_bytes = 1024;
> > +module_param(copy_bytes, uint, 0644);
> > +MODULE_PARM_DESC(copy_bytes, "Threshold under which NTB will use the CPU to copy instead of DMA");
> > +
> > struct ntb_queue_entry {
> > /* ntb_queue list reference */
> > struct list_head entry;
> > @@ -76,6 +81,13 @@ struct ntb_queue_entry {
> > void *buf;
> > unsigned int len;
> > unsigned int flags;
> > +
> > + struct ntb_transport_qp *qp;
> > + union {
> > + struct ntb_payload_header __iomem *tx_hdr;
> > + struct ntb_payload_header *rx_hdr;
> > + };
> > + unsigned int index;
> > };
> >
> > struct ntb_rx_info {
> > @@ -86,6 +98,7 @@ struct ntb_transport_qp {
> > struct ntb_transport *transport;
> > struct ntb_device *ndev;
> > void *cb_data;
> > + struct dma_chan *dma_chan;
> >
> > bool client_ready;
> > bool qp_link;
> > @@ -99,6 +112,7 @@ struct ntb_transport_qp {
> > struct list_head tx_free_q;
> > spinlock_t ntb_tx_free_q_lock;
> > void __iomem *tx_mw;
> > + dma_addr_t tx_mw_raw;
> > unsigned int tx_index;
> > unsigned int tx_max_entry;
> > unsigned int tx_max_frame;
> > @@ -114,6 +128,7 @@ struct ntb_transport_qp {
> > unsigned int rx_index;
> > unsigned int rx_max_entry;
> > unsigned int rx_max_frame;
> > + dma_cookie_t last_cookie;
> >
> > void (*event_handler) (void *data, int status);
> > struct delayed_work link_work;
> > @@ -129,9 +144,14 @@ struct ntb_transport_qp {
> > u64 rx_err_no_buf;
> > u64 rx_err_oflow;
> > u64 rx_err_ver;
> > + u64 rx_memcpy;
> > + u64 rx_async;
> > u64 tx_bytes;
> > u64 tx_pkts;
> > u64 tx_ring_full;
> > + u64 tx_err_no_buf;
> > + u64 tx_memcpy;
> > + u64 tx_async;
> > };
> >
> > struct ntb_transport_mw {
> > @@ -381,7 +401,7 @@ static ssize_t debugfs_read(struct file *filp, char __user *ubuf, size_t count,
> > char *buf;
> > ssize_t ret, out_offset, out_count;
> >
> > - out_count = 600;
> > + out_count = 1000;
> >
> > buf = kmalloc(out_count, GFP_KERNEL);
> > if (!buf)
> > @@ -396,6 +416,10 @@ static ssize_t debugfs_read(struct file *filp, char __user *ubuf, size_t count,
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "rx_pkts - \t%llu\n", qp->rx_pkts);
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > + "rx_memcpy - \t%llu\n", qp->rx_memcpy);
> > + out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > + "rx_async - \t%llu\n", qp->rx_async);
> > + out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "rx_ring_empty - %llu\n", qp->rx_ring_empty);
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "rx_err_no_buf - %llu\n", qp->rx_err_no_buf);
> > @@ -415,8 +439,14 @@ static ssize_t debugfs_read(struct file *filp, char __user *ubuf, size_t count,
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "tx_pkts - \t%llu\n", qp->tx_pkts);
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > + "tx_memcpy - \t%llu\n", qp->tx_memcpy);
> > + out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > + "tx_async - \t%llu\n", qp->tx_async);
> > + out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "tx_ring_full - \t%llu\n", qp->tx_ring_full);
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > + "tx_err_no_buf - %llu\n", qp->tx_err_no_buf);
> > + out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "tx_mw - \t%p\n", qp->tx_mw);
> > out_offset += snprintf(buf + out_offset, out_count - out_offset,
> > "tx_index - \t%u\n", qp->tx_index);
> > @@ -488,11 +518,11 @@ static void ntb_transport_setup_qp_mw(struct ntb_transport *nt,
> > num_qps_mw = nt->max_qps / mw_max;
> >
> > rx_size = (unsigned int) nt->mw[mw_num].size / num_qps_mw;
> > - qp->remote_rx_info = nt->mw[mw_num].virt_addr +
> > - (qp_num / mw_max * rx_size);
> > + qp->rx_buff = nt->mw[mw_num].virt_addr + qp_num / mw_max * rx_size;
> > rx_size -= sizeof(struct ntb_rx_info);
> >
> > - qp->rx_buff = qp->remote_rx_info + 1;
> > + qp->remote_rx_info = qp->rx_buff + rx_size;
> > +
> > /* Due to housekeeping, there must be atleast 2 buffs */
> > qp->rx_max_frame = min(transport_mtu, rx_size / 2);
> > qp->rx_max_entry = rx_size / qp->rx_max_frame;
> > @@ -802,6 +832,7 @@ static void ntb_transport_init_queue(struct ntb_transport *nt,
> > struct ntb_transport_qp *qp;
> > unsigned int num_qps_mw, tx_size;
> > u8 mw_num, mw_max;
> > + u64 qp_offset;
> >
> > mw_max = ntb_max_mw(nt->ndev);
> > mw_num = QP_TO_MW(nt->ndev, qp_num);
> > @@ -820,11 +851,12 @@ static void ntb_transport_init_queue(struct ntb_transport *nt,
> > num_qps_mw = nt->max_qps / mw_max;
> >
> > tx_size = (unsigned int) ntb_get_mw_size(qp->ndev, mw_num) / num_qps_mw;
> > - qp->rx_info = ntb_get_mw_vbase(nt->ndev, mw_num) +
> > - (qp_num / mw_max * tx_size);
> > + qp_offset = qp_num / mw_max * tx_size;
> > + qp->tx_mw = ntb_get_mw_vbase(nt->ndev, mw_num) + qp_offset;
> > + qp->tx_mw_raw = ntb_get_mw_base(qp->ndev, mw_num) + qp_offset;
>
> Just a quibble with the name, why "raw" instead of "phys"?

What's in a name? ;-)

phys is fine.

>
> > tx_size -= sizeof(struct ntb_rx_info);
> > + qp->rx_info = qp->tx_mw + tx_size;
> >
> > - qp->tx_mw = qp->rx_info + 1;
> > /* Due to housekeeping, there must be atleast 2 buffs */
> > qp->tx_max_frame = min(transport_mtu, tx_size / 2);
> > qp->tx_max_entry = tx_size / qp->tx_max_frame;
> > @@ -956,13 +988,22 @@ void ntb_transport_free(void *transport)
> > kfree(nt);
> > }
> >
> > -static void ntb_rx_copy_task(struct ntb_transport_qp *qp,
> > - struct ntb_queue_entry *entry, void *offset)
> > +static void ntb_rx_copy_callback(void *data)
> > {
> > + struct ntb_queue_entry *entry = data;
> > + struct ntb_transport_qp *qp = entry->qp;
> > void *cb_data = entry->cb_data;
> > unsigned int len = entry->len;
> > + struct ntb_payload_header *hdr = entry->rx_hdr;
> > +
> > + wmb();
>
> What is this barrier paired with?

You will see a wmb being removed from ntb_process_rxc below. It is
VERY necessary to be here.

> > + hdr->flags = 0;
> >
> > - memcpy(entry->buf, offset, entry->len);
> > + /* If the callbacks come out of order, the writing of the index to the
> > + * last completed will be out of order. This may result in the the
> > + * receive stalling forever.
> > + */
>
> Is this for the case where we are bouncing back and forth between
> sync/async? Otherwise I do not see how transactions could get out of
> order given you allocate a channel once per queue. Is this comment
> saying that the iowrite32 is somehow a fix, or is this comment a
> FIXME?

There is a case for a mix, the "copy_bytes" variable above switches to
CPU for small transfers (which greatly increases throughput on small
transfers). The caveat to it is the need to flush the DMA engine to
prevent out-of-order. This comment is mainly an reminder of this issue.

> > + iowrite32(entry->index, &qp->rx_info->entry);
> >
> > ntb_list_add(&qp->ntb_rx_free_q_lock, &entry->entry, &qp->rx_free_q);
> >
> > @@ -970,6 +1011,80 @@ static void ntb_rx_copy_task(struct ntb_transport_qp *qp,
> > qp->rx_handler(qp, qp->cb_data, cb_data, len);
> > }
> >
> > +static void ntb_memcpy_rx(struct ntb_queue_entry *entry, void *offset)
> > +{
> > + void *buf = entry->buf;
> > + size_t len = entry->len;
> > +
> > + memcpy(buf, offset, len);
> > +
> > + ntb_rx_copy_callback(entry);
> > +}
> > +
> > +static void ntb_async_rx(struct ntb_queue_entry *entry, void *offset,
> > + size_t len)
> > +{
> > + struct dma_async_tx_descriptor *txd;
> > + struct ntb_transport_qp *qp = entry->qp;
> > + struct dma_chan *chan = qp->dma_chan;
> > + struct dma_device *device;
> > + dma_addr_t src, dest;
> > + dma_cookie_t cookie;
> > + void *buf = entry->buf;
> > + unsigned long flags;
> > +
> > + entry->len = len;
> > +
> > + if (!chan)
> > + goto err;
> > +
> > + device = chan->device;
> > +
> > + if (len < copy_bytes ||
> > + !is_dma_copy_aligned(device, __pa(offset), __pa(buf), len))
>
> __pa()'s necessary here? I don't think the alignment requirements
> will ever cross PAGE_OFFSET.

The __pa calls cast the void* to an unsigned long, thus keeping
is_dma_copy_aligned happy.

> > + goto err1;
> > +
> > + dest = dma_map_single(device->dev, buf, len, DMA_FROM_DEVICE);
> > + if (dma_mapping_error(device->dev, dest))
> > + goto err1;
> > +
> > + src = dma_map_single(device->dev, offset, len, DMA_TO_DEVICE);
> > + if (dma_mapping_error(device->dev, src))
> > + goto err2;
> > +
> > + flags = DMA_COMPL_DEST_UNMAP_SINGLE | DMA_COMPL_SRC_UNMAP_SINGLE |
> > + DMA_PREP_INTERRUPT;
> > + txd = device->device_prep_dma_memcpy(chan, dest, src, len, flags);
> > + if (!txd)
> > + goto err3;
> > +
> > + txd_clear_parent(txd);
> > + txd_clear_next(txd);
>
> Neither of these should be necessary.

I had crashes in early versions of the code without them, but a quick
test with the removed doesn't show any issues. Good catch.

> > + txd->callback = ntb_rx_copy_callback;
> > + txd->callback_param = entry;
> > +
> > + cookie = dmaengine_submit(txd);
> > + if (dma_submit_error(cookie))
> > + goto err3;
> > +
> > + qp->last_cookie = cookie;
> > +
> > + dma_async_issue_pending(chan);
>
> hmm... can this go in ntb_process_rx() so that the submission is
> batched? Cuts down on mmio.

I moved it down to ntb_transport_rx (after the calls to
ntb_process_rxc), and the performance seems to be roughly the same.

> > + qp->rx_async++;
> > +
> > + return;
> > +
> > +err3:
> > + dma_unmap_single(device->dev, src, len, DMA_TO_DEVICE);
> > +err2:
> > + dma_unmap_single(device->dev, dest, len, DMA_FROM_DEVICE);
> > +err1:
> > + dma_sync_wait(chan, qp->last_cookie);
> > +err:
> > + ntb_memcpy_rx(entry, offset);
> > + qp->rx_memcpy++;
> > +}
> > +
> > static int ntb_process_rxc(struct ntb_transport_qp *qp)
> > {
> > struct ntb_payload_header *hdr;
> > @@ -1008,41 +1123,44 @@ static int ntb_process_rxc(struct ntb_transport_qp *qp)
> > if (hdr->flags & LINK_DOWN_FLAG) {
> > ntb_qp_link_down(qp);
> >
> > - ntb_list_add(&qp->ntb_rx_pend_q_lock, &entry->entry,
> > - &qp->rx_pend_q);
> > - goto out;
> > + goto err;
> > }
> >
> > dev_dbg(&ntb_query_pdev(qp->ndev)->dev,
> > "rx offset %u, ver %u - %d payload received, buf size %d\n",
> > qp->rx_index, hdr->ver, hdr->len, entry->len);
> >
> > - if (hdr->len <= entry->len) {
> > - entry->len = hdr->len;
> > - ntb_rx_copy_task(qp, entry, offset);
> > - } else {
> > - ntb_list_add(&qp->ntb_rx_pend_q_lock, &entry->entry,
> > - &qp->rx_pend_q);
> > + qp->rx_bytes += hdr->len;
> > + qp->rx_pkts++;
> >
> > + if (hdr->len > entry->len) {
> > qp->rx_err_oflow++;
> > dev_dbg(&ntb_query_pdev(qp->ndev)->dev,
> > "RX overflow! Wanted %d got %d\n",
> > hdr->len, entry->len);
> > +
> > + goto err;
> > }
> >
> > - qp->rx_bytes += hdr->len;
> > - qp->rx_pkts++;
> > + entry->index = qp->rx_index;
> > + entry->rx_hdr = hdr;
> >
> > -out:
> > - /* Ensure that the data is fully copied out before clearing the flag */
> > - wmb();
> > - hdr->flags = 0;
> > - iowrite32(qp->rx_index, &qp->rx_info->entry);
> > + ntb_async_rx(entry, offset, hdr->len);
> >
> > +out:
> > qp->rx_index++;
> > qp->rx_index %= qp->rx_max_entry;
> >
> > return 0;
> > +
> > +err:
> > + ntb_list_add(&qp->ntb_rx_pend_q_lock, &entry->entry,
> > + &qp->rx_pend_q);
> > + wmb();
> > + hdr->flags = 0;
> > + iowrite32(qp->rx_index, &qp->rx_info->entry);
> > +
> > + goto out;
> > }
> >
> > static void ntb_transport_rx(unsigned long data)
> > @@ -1070,19 +1188,12 @@ static void ntb_transport_rxc_db(void *data, int db_num)
> > tasklet_schedule(&qp->rx_work);
> > }
> >
> > -static void ntb_tx_copy_task(struct ntb_transport_qp *qp,
> > - struct ntb_queue_entry *entry,
> > - void __iomem *offset)
> > +static void ntb_tx_copy_callback(void *data)
> > {
> > - struct ntb_payload_header __iomem *hdr;
> > -
> > - memcpy_toio(offset, entry->buf, entry->len);
> > -
> > - hdr = offset + qp->tx_max_frame - sizeof(struct ntb_payload_header);
> > - iowrite32(entry->len, &hdr->len);
> > - iowrite32((u32) qp->tx_pkts, &hdr->ver);
> > + struct ntb_queue_entry *entry = data;
> > + struct ntb_transport_qp *qp = entry->qp;
> > + struct ntb_payload_header __iomem *hdr = entry->tx_hdr;
> >
> > - /* Ensure that the data is fully copied out before setting the flag */
> > wmb();
> > iowrite32(entry->flags | DESC_DONE_FLAG, &hdr->flags);
> >
> > @@ -1103,15 +1214,79 @@ static void ntb_tx_copy_task(struct ntb_transport_qp *qp,
> > ntb_list_add(&qp->ntb_tx_free_q_lock, &entry->entry, &qp->tx_free_q);
> > }
> >
> > -static int ntb_process_tx(struct ntb_transport_qp *qp,
> > - struct ntb_queue_entry *entry)
> > +static void ntb_memcpy_tx(struct ntb_queue_entry *entry, void __iomem *offset)
> > +{
> > + memcpy_toio(offset, entry->buf, entry->len);
> > +
> > + ntb_tx_copy_callback(entry);
> > +}
> > +
> > +static void ntb_async_tx(struct ntb_transport_qp *qp,
> > + struct ntb_queue_entry *entry)
> > {
> > + struct dma_async_tx_descriptor *txd;
> > + struct dma_chan *chan = qp->dma_chan;
> > + struct dma_device *device;
> > + dma_addr_t src, dest;
> > + dma_cookie_t cookie;
> > + struct ntb_payload_header __iomem *hdr;
> > void __iomem *offset;
> > + size_t len = entry->len;
> > + void *buf = entry->buf;
> > + unsigned long flags;
> >
> > offset = qp->tx_mw + qp->tx_max_frame * qp->tx_index;
> > + hdr = offset + qp->tx_max_frame - sizeof(struct ntb_payload_header);
> > + entry->tx_hdr = hdr;
> > +
> > + iowrite32(entry->len, &hdr->len);
> > + iowrite32((u32) qp->tx_pkts, &hdr->ver);
> > +
> > + if (!chan)
> > + goto err;
> >
> > - dev_dbg(&ntb_query_pdev(qp->ndev)->dev, "%lld - offset %p, tx %u, entry len %d flags %x buff %p\n",
> > - qp->tx_pkts, offset, qp->tx_index, entry->len, entry->flags,
> > + device = chan->device;
> > +
> > + dest = qp->tx_mw_raw + qp->tx_max_frame * qp->tx_index;
> > +
> > + if (len < copy_bytes ||
> > + !is_dma_copy_aligned(device, __pa(buf), dest, len))
>
> ditto on the use of __pa here.
>
> > + goto err;
> > +
> > + src = dma_map_single(device->dev, buf, len, DMA_TO_DEVICE);
> > + if (dma_mapping_error(device->dev, src))
> > + goto err;
> > +
> > + flags = DMA_COMPL_SRC_UNMAP_SINGLE | DMA_PREP_INTERRUPT;
> > + txd = device->device_prep_dma_memcpy(chan, dest, src, len, flags);
> > + if (!txd)
> > + goto err1;
> > +
> > + txd_clear_parent(txd);
> > + txd_clear_next(txd);
>
> ...again not needed.
>
> > + txd->callback = ntb_tx_copy_callback;
> > + txd->callback_param = entry;
> > +
> > + cookie = dmaengine_submit(txd);
> > + if (dma_submit_error(cookie))
> > + goto err1;
> > +
> > + dma_async_issue_pending(chan);
> > + qp->tx_async++;
> > +
> > + return;
> > +err1:
> > + dma_unmap_single(device->dev, src, len, DMA_TO_DEVICE);
> > +err:
> > + ntb_memcpy_tx(entry, offset);
> > + qp->tx_memcpy++;
> > +}
> > +
> > +static int ntb_process_tx(struct ntb_transport_qp *qp,
> > + struct ntb_queue_entry *entry)
> > +{
> > + dev_dbg(&ntb_query_pdev(qp->ndev)->dev, "%lld - tx %u, entry len %d flags %x buff %p\n",
> > + qp->tx_pkts, qp->tx_index, entry->len, entry->flags,
> > entry->buf);
> > if (qp->tx_index == qp->remote_rx_info->entry) {
> > qp->tx_ring_full++;
> > @@ -1127,7 +1302,7 @@ static int ntb_process_tx(struct ntb_transport_qp *qp,
> > return 0;
> > }
> >
> > - ntb_tx_copy_task(qp, entry, offset);
> > + ntb_async_tx(qp, entry);
> >
> > qp->tx_index++;
> > qp->tx_index %= qp->tx_max_entry;
> > @@ -1213,11 +1388,16 @@ ntb_transport_create_queue(void *data, struct pci_dev *pdev,
> > qp->tx_handler = handlers->tx_handler;
> > qp->event_handler = handlers->event_handler;
> >
> > + qp->dma_chan = dma_find_channel(DMA_MEMCPY);
> > + if (!qp->dma_chan)
> > + dev_info(&pdev->dev, "Unable to allocate private DMA channel, using CPU instead\n");
>
> You can drop "private" since this is a public allocation.

Good catch

> > +
> > for (i = 0; i < NTB_QP_DEF_NUM_ENTRIES; i++) {
> > entry = kzalloc(sizeof(struct ntb_queue_entry), GFP_ATOMIC);
> > if (!entry)
> > goto err1;
> >
> > + entry->qp = qp;
> > ntb_list_add(&qp->ntb_rx_free_q_lock, &entry->entry,
> > &qp->rx_free_q);
> > }
> > @@ -1227,6 +1407,7 @@ ntb_transport_create_queue(void *data, struct pci_dev *pdev,
> > if (!entry)
> > goto err2;
> >
> > + entry->qp = qp;
> > ntb_list_add(&qp->ntb_tx_free_q_lock, &entry->entry,
> > &qp->tx_free_q);
> > }
> > @@ -1272,11 +1453,14 @@ void ntb_transport_free_queue(struct ntb_transport_qp *qp)
> >
> > pdev = ntb_query_pdev(qp->ndev);
> >
> > - cancel_delayed_work_sync(&qp->link_work);
> > + if (qp->dma_chan)
> > + dmaengine_terminate_all(qp->dma_chan);
>
> Do you need this or can you just wait for all outstanding tx / rx to quiesce?

I'd prefer not to spin in the shutdown code waiting for the channel to
quiesce. I suppose I could be nice and give it a small time to do so,
before I smash it in the head with a rock.

> > ntb_unregister_db_callback(qp->ndev, qp->qp_num);
> > tasklet_disable(&qp->rx_work);
> >
> > + cancel_delayed_work_sync(&qp->link_work);
> > +
> > while ((entry = ntb_list_rm(&qp->ntb_rx_free_q_lock, &qp->rx_free_q)))
> > kfree(entry);
> >
> > @@ -1382,8 +1566,10 @@ int ntb_transport_tx_enqueue(struct ntb_transport_qp *qp, void *cb, void *data,
> > return -EINVAL;
> >
> > entry = ntb_list_rm(&qp->ntb_tx_free_q_lock, &qp->tx_free_q);
> > - if (!entry)
> > + if (!entry) {
> > + qp->tx_err_no_buf++;
> > return -ENOMEM;
> > + }
> >
> > entry->cb_data = cb;
> > entry->buf = data;
> > @@ -1499,9 +1685,18 @@ EXPORT_SYMBOL_GPL(ntb_transport_qp_num);
> > */
> > unsigned int ntb_transport_max_size(struct ntb_transport_qp *qp)
> > {
> > + unsigned int max;
> > +
> > if (!qp)
> > return 0;
> >
> > - return qp->tx_max_frame - sizeof(struct ntb_payload_header);
> > + if (!qp->dma_chan)
> > + return qp->tx_max_frame - sizeof(struct ntb_payload_header);
> > +
> > + /* If DMA engine usage is possible, try to find the max size for that */
> > + max = qp->tx_max_frame - sizeof(struct ntb_payload_header);
> > + max -= max % (1 << qp->dma_chan->device->copy_align);
>
> Unless I missed it you need a dmaengine_get() dmaengine_put() pair in
> your driver setup/teardown. dmaengine_get() notifies dmaengine of a
> dma_find_channel() user.

Good catch.

Thanks for the review! I'll make the changes and do another spin of
the patch.

Thanks,
Jon