@@ -26,6 +26,7 @@ config TEHUTI
config TEHUTI_TN40
tristate "Tehuti Networks TN40xx 10G Ethernet adapters"
depends on PCI
+ select PAGE_POOL
select FW_LOADER
help
This driver supports 10G Ethernet adapters using Tehuti Networks
@@ -8,6 +8,7 @@
#include <linux/netdevice.h>
#include <linux/pci.h>
#include <linux/vmalloc.h>
+#include <net/page_pool/helpers.h>
#include "tn40.h"
@@ -62,6 +63,348 @@ static void tn40_fifo_free(struct tn40_priv *priv, struct tn40_fifo *f)
f->memsz + TN40_FIFO_EXTRA_SPACE, f->va, f->da);
}
+static struct tn40_rxdb *tn40_rxdb_alloc(int nelem)
+{
+ size_t size = sizeof(struct tn40_rxdb) + (nelem * sizeof(int)) +
+ (nelem * sizeof(struct tn40_rx_map));
+ struct tn40_rxdb *db;
+ int i;
+
+ db = vzalloc(size);
+ if (db) {
+ db->stack = (int *)(db + 1);
+ db->elems = (void *)(db->stack + nelem);
+ db->nelem = nelem;
+ db->top = nelem;
+ /* make the first alloc close to db struct */
+ for (i = 0; i < nelem; i++)
+ db->stack[i] = nelem - i - 1;
+ }
+ return db;
+}
+
+static void tn40_rxdb_free(struct tn40_rxdb *db)
+{
+ vfree(db);
+}
+
+static int tn40_rxdb_alloc_elem(struct tn40_rxdb *db)
+{
+ return db->stack[--db->top];
+}
+
+static void *tn40_rxdb_addr_elem(struct tn40_rxdb *db, unsigned int n)
+{
+ return db->elems + n;
+}
+
+static int tn40_rxdb_available(struct tn40_rxdb *db)
+{
+ return db->top;
+}
+
+static void tn40_rxdb_free_elem(struct tn40_rxdb *db, unsigned int n)
+{
+ db->stack[db->top++] = n;
+}
+
+/**
+ * tn40_create_rx_ring - Initialize RX all related HW and SW resources
+ * @priv: NIC private structure
+ *
+ * create_rx_ring creates rxf and rxd fifos, updates the relevant HW registers,
+ * preallocates skbs for rx. It assumes that Rx is disabled in HW funcs are
+ * grouped for better cache usage
+ *
+ * RxD fifo is smaller then RxF fifo by design. Upon high load, RxD will be
+ * filled and packets will be dropped by the NIC without getting into the host
+ * or generating interrupts. In this situation the host has no chance of
+ * processing all the packets. Dropping packets by the NIC is cheaper, since it
+ * takes 0 CPU cycles.
+ *
+ * Return: 0 on success and negative value on error.
+ */
+static int tn40_create_rx_ring(struct tn40_priv *priv)
+{
+ struct page_pool_params pp = {
+ .dev = &priv->pdev->dev,
+ .napi = &priv->napi,
+ .dma_dir = DMA_FROM_DEVICE,
+ .netdev = priv->ndev,
+ .flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
+ .max_len = PAGE_SIZE,
+ };
+ int ret, pkt_size, nr;
+
+ priv->page_pool = page_pool_create(&pp);
+ if (IS_ERR(priv->page_pool))
+ return PTR_ERR(priv->page_pool);
+
+ ret = tn40_fifo_alloc(priv, &priv->rxd_fifo0.m, priv->rxd_size,
+ TN40_REG_RXD_CFG0_0, TN40_REG_RXD_CFG1_0,
+ TN40_REG_RXD_RPTR_0, TN40_REG_RXD_WPTR_0);
+ if (ret)
+ goto err_destroy_page_pool;
+
+ ret = tn40_fifo_alloc(priv, &priv->rxf_fifo0.m, priv->rxf_size,
+ TN40_REG_RXF_CFG0_0, TN40_REG_RXF_CFG1_0,
+ TN40_REG_RXF_RPTR_0, TN40_REG_RXF_WPTR_0);
+ if (ret)
+ goto err_free_rxd;
+
+ pkt_size = priv->ndev->mtu + VLAN_ETH_HLEN;
+ priv->rxf_fifo0.m.pktsz = pkt_size;
+ nr = priv->rxf_fifo0.m.memsz / sizeof(struct tn40_rxf_desc);
+ priv->rxdb0 = tn40_rxdb_alloc(nr);
+ if (!priv->rxdb0) {
+ ret = -ENOMEM;
+ goto err_free_rxf;
+ }
+ return 0;
+err_free_rxf:
+ tn40_fifo_free(priv, &priv->rxf_fifo0.m);
+err_free_rxd:
+ tn40_fifo_free(priv, &priv->rxd_fifo0.m);
+err_destroy_page_pool:
+ page_pool_destroy(priv->page_pool);
+ return ret;
+}
+
+static void tn40_rx_free_buffers(struct tn40_priv *priv)
+{
+ struct tn40_rxdb *db = priv->rxdb0;
+ struct tn40_rx_map *dm;
+ u16 i;
+
+ netdev_dbg(priv->ndev, "total =%d free =%d busy =%d\n", db->nelem,
+ tn40_rxdb_available(db),
+ db->nelem - tn40_rxdb_available(db));
+
+ for (i = 0; i < db->nelem; i++) {
+ dm = tn40_rxdb_addr_elem(db, i);
+ if (dm->page)
+ page_pool_put_full_page(priv->page_pool, dm->page,
+ false);
+ }
+}
+
+static void tn40_destroy_rx_ring(struct tn40_priv *priv)
+{
+ if (priv->rxdb0) {
+ tn40_rx_free_buffers(priv);
+ tn40_rxdb_free(priv->rxdb0);
+ priv->rxdb0 = NULL;
+ }
+ tn40_fifo_free(priv, &priv->rxf_fifo0.m);
+ tn40_fifo_free(priv, &priv->rxd_fifo0.m);
+ page_pool_destroy(priv->page_pool);
+}
+
+static void tn40_set_rx_desc(struct tn40_priv *priv, int idx, u64 dma)
+{
+ struct tn40_rxf_fifo *f = &priv->rxf_fifo0;
+ struct tn40_rxf_desc *rxfd;
+ int delta;
+
+ rxfd = (struct tn40_rxf_desc *)(f->m.va + f->m.wptr);
+ rxfd->info = cpu_to_le32(0x10003); /* INFO =1 BC =3 */
+ rxfd->va_lo = cpu_to_le32(idx);
+ rxfd->pa_lo = cpu_to_le32(lower_32_bits(dma));
+ rxfd->pa_hi = cpu_to_le32(upper_32_bits(dma));
+ rxfd->len = cpu_to_le32(f->m.pktsz);
+ f->m.wptr += sizeof(struct tn40_rxf_desc);
+ delta = f->m.wptr - f->m.memsz;
+ if (unlikely(delta >= 0)) {
+ f->m.wptr = delta;
+ if (delta > 0) {
+ memcpy(f->m.va, f->m.va + f->m.memsz, delta);
+ netdev_dbg(priv->ndev,
+ "wrapped rxd descriptor\n");
+ }
+ }
+}
+
+/**
+ * tn40_rx_alloc_buffers - Fill rxf fifo with buffers.
+ *
+ * @priv: NIC's private structure
+ *
+ * rx_alloc_buffers allocates buffers via the page pool API, builds rxf descs
+ * and pushes them (rxf descr) into the rxf fifo. The pages are stored in rxdb.
+ * To calculate the free space, we uses the cached values of RPTR and WPTR
+ * when needed. This function also updates RPTR and WPTR.
+ */
+static void tn40_rx_alloc_buffers(struct tn40_priv *priv)
+{
+ struct tn40_rxf_fifo *f = &priv->rxf_fifo0;
+ struct tn40_rxdb *db = priv->rxdb0;
+ struct tn40_rx_map *dm;
+ struct page *page;
+ int dno, i, idx;
+
+ dno = tn40_rxdb_available(db) - 1;
+ for (i = dno; i > 0; i--) {
+ page = page_pool_dev_alloc_pages(priv->page_pool);
+ if (!page)
+ break;
+
+ idx = tn40_rxdb_alloc_elem(db);
+ tn40_set_rx_desc(priv, idx, page_pool_get_dma_addr(page));
+ dm = tn40_rxdb_addr_elem(db, idx);
+ dm->page = page;
+ }
+ if (i != dno)
+ tn40_write_reg(priv, f->m.reg_wptr,
+ f->m.wptr & TN40_TXF_WPTR_WR_PTR);
+ netdev_dbg(priv->ndev, "write_reg 0x%04x f->m.reg_wptr 0x%x\n",
+ f->m.reg_wptr, f->m.wptr & TN40_TXF_WPTR_WR_PTR);
+ netdev_dbg(priv->ndev, "read_reg 0x%04x f->m.reg_rptr=0x%x\n",
+ f->m.reg_rptr, tn40_read_reg(priv, f->m.reg_rptr));
+ netdev_dbg(priv->ndev, "write_reg 0x%04x f->m.reg_wptr=0x%x\n",
+ f->m.reg_wptr, tn40_read_reg(priv, f->m.reg_wptr));
+}
+
+static void tn40_recycle_rx_buffer(struct tn40_priv *priv,
+ struct tn40_rxd_desc *rxdd)
+{
+ struct tn40_rxf_fifo *f = &priv->rxf_fifo0;
+ struct tn40_rx_map *dm;
+ int idx;
+
+ idx = le32_to_cpu(rxdd->va_lo);
+ dm = tn40_rxdb_addr_elem(priv->rxdb0, idx);
+ tn40_set_rx_desc(priv, idx, page_pool_get_dma_addr(dm->page));
+
+ tn40_write_reg(priv, f->m.reg_wptr, f->m.wptr & TN40_TXF_WPTR_WR_PTR);
+}
+
+static int tn40_rx_receive(struct tn40_priv *priv, int budget)
+{
+ struct tn40_rxd_fifo *f = &priv->rxd_fifo0;
+ u32 rxd_val1, rxd_err, pkt_id;
+ int tmp_len, size, done = 0;
+ struct tn40_rxdb *db = NULL;
+ struct tn40_rxd_desc *rxdd;
+ struct tn40_rx_map *dm;
+ struct sk_buff *skb;
+ u16 len, rxd_vlan;
+ int idx;
+
+ f->m.wptr = tn40_read_reg(priv, f->m.reg_wptr) & TN40_TXF_WPTR_WR_PTR;
+ size = f->m.wptr - f->m.rptr;
+ if (size < 0)
+ size += f->m.memsz; /* Size is negative :-) */
+
+ while (size > 0) {
+ rxdd = (struct tn40_rxd_desc *)(f->m.va + f->m.rptr);
+ db = priv->rxdb0;
+
+ /* We have a chicken and egg problem here. If the
+ * descriptor is wrapped we first need to copy the tail
+ * of the descriptor to the end of the buffer before
+ * extracting values from the descriptor. However in
+ * order to know if the descriptor is wrapped we need to
+ * obtain the length of the descriptor from (the
+ * wrapped) descriptor. Luckily the length is the first
+ * word of the descriptor. Descriptor lengths are
+ * multiples of 8 bytes so in case of a wrapped
+ * descriptor the first 8 bytes guaranteed to appear
+ * before the end of the buffer. We first obtain the
+ * length, we then copy the rest of the descriptor if
+ * needed and then extract the rest of the values from
+ * the descriptor.
+ *
+ * Do not change the order of operations as it will
+ * break the code!!!
+ */
+ rxd_val1 = le32_to_cpu(rxdd->rxd_val1);
+ tmp_len = TN40_GET_RXD_BC(rxd_val1) << 3;
+ pkt_id = TN40_GET_RXD_PKT_ID(rxd_val1);
+ size -= tmp_len;
+ /* CHECK FOR A PARTIALLY ARRIVED DESCRIPTOR */
+ if (size < 0) {
+ netdev_dbg(priv->ndev,
+ "%s partially arrived desc tmp_len %d\n",
+ __func__, tmp_len);
+ break;
+ }
+ /* make sure that the descriptor fully is arrived
+ * before reading the rest of the descriptor.
+ */
+ rmb();
+
+ /* A special treatment is given to non-contiguous
+ * descriptors that start near the end, wraps around
+ * and continue at the beginning. The second part is
+ * copied right after the first, and then descriptor
+ * is interpreted as normal. The fifo has an extra
+ * space to allow such operations.
+ */
+
+ /* HAVE WE REACHED THE END OF THE QUEUE? */
+ f->m.rptr += tmp_len;
+ tmp_len = f->m.rptr - f->m.memsz;
+ if (unlikely(tmp_len >= 0)) {
+ f->m.rptr = tmp_len;
+ if (tmp_len > 0) {
+ /* COPY PARTIAL DESCRIPTOR
+ * TO THE END OF THE QUEUE
+ */
+ netdev_dbg(priv->ndev,
+ "wrapped desc rptr=%d tmp_len=%d\n",
+ f->m.rptr, tmp_len);
+ memcpy(f->m.va + f->m.memsz, f->m.va, tmp_len);
+ }
+ }
+ idx = le32_to_cpu(rxdd->va_lo);
+ dm = tn40_rxdb_addr_elem(db, idx);
+ prefetch(dm);
+
+ len = le16_to_cpu(rxdd->len);
+ rxd_vlan = le16_to_cpu(rxdd->rxd_vlan);
+ /* CHECK FOR ERRORS */
+ rxd_err = TN40_GET_RXD_ERR(rxd_val1);
+ if (unlikely(rxd_err)) {
+ netdev_err(priv->ndev, "rxd_err = 0x%x\n", rxd_err);
+ priv->net_stats.rx_errors++;
+ tn40_recycle_rx_buffer(priv, rxdd);
+ continue;
+ }
+
+ skb = napi_build_skb(page_address(dm->page), PAGE_SIZE);
+ if (!skb) {
+ netdev_err(priv->ndev, "napi_build_skb() failed\n");
+ priv->net_stats.rx_dropped++;
+ tn40_recycle_rx_buffer(priv, rxdd);
+ break;
+ }
+ skb_mark_for_recycle(skb);
+ skb_put(skb, len);
+ skb->protocol = eth_type_trans(skb, priv->ndev);
+ skb->ip_summed =
+ (pkt_id == 0) ? CHECKSUM_NONE : CHECKSUM_UNNECESSARY;
+ if (TN40_GET_RXD_VTAG(rxd_val1))
+ __vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q),
+ TN40_GET_RXD_VLAN_TCI(rxd_vlan));
+
+ dm->page = NULL;
+ tn40_rxdb_free_elem(db, idx);
+
+ napi_gro_receive(&priv->napi, skb);
+
+ priv->net_stats.rx_bytes += len;
+
+ if (unlikely(++done >= budget))
+ break;
+ }
+
+ priv->net_stats.rx_packets += done;
+ /* FIXME: Do something to minimize pci accesses */
+ tn40_write_reg(priv, f->m.reg_rptr, f->m.rptr & TN40_TXF_WPTR_WR_PTR);
+ tn40_rx_alloc_buffers(priv);
+ return done;
+}
+
/* TX HW/SW interaction overview
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* There are 2 types of TX communication channels between driver and NIC.
@@ -450,6 +793,56 @@ static int tn40_start_xmit(struct sk_buff *skb, struct net_device *ndev)
return NETDEV_TX_OK;
}
+static void tn40_tx_cleanup(struct tn40_priv *priv)
+{
+ struct tn40_txf_fifo *f = &priv->txf_fifo0;
+ struct tn40_txdb *db = &priv->txdb;
+ int tx_level = 0;
+
+ f->m.wptr = tn40_read_reg(priv, f->m.reg_wptr) & TN40_TXF_WPTR_MASK;
+
+ netif_tx_lock(priv->ndev);
+ while (f->m.wptr != f->m.rptr) {
+ f->m.rptr += TN40_TXF_DESC_SZ;
+ f->m.rptr &= f->m.size_mask;
+ /* Unmap all fragments */
+ /* First has to come tx_maps containing DMA */
+ do {
+ dma_unmap_page(&priv->pdev->dev, db->rptr->addr.dma,
+ db->rptr->len, DMA_TO_DEVICE);
+ tn40_tx_db_inc_rptr(db);
+ } while (db->rptr->len > 0);
+ tx_level -= db->rptr->len; /* '-' Because the len is negative */
+
+ /* Now should come skb pointer - free it */
+ dev_kfree_skb_any(db->rptr->addr.skb);
+ netdev_dbg(priv->ndev, "dev_kfree_skb_any %p %d\n",
+ db->rptr->addr.skb, -db->rptr->len);
+ tn40_tx_db_inc_rptr(db);
+ }
+
+ /* Let the HW know which TXF descriptors were cleaned */
+ tn40_write_reg(priv, f->m.reg_rptr, f->m.rptr & TN40_TXF_WPTR_WR_PTR);
+
+ /* We reclaimed resources, so in case the Q is stopped by xmit
+ * callback, we resume the transmission and use tx_lock to
+ * synchronize with xmit.
+ */
+ priv->tx_level += tx_level;
+ if (priv->tx_noupd) {
+ priv->tx_noupd = 0;
+ tn40_write_reg(priv, priv->txd_fifo0.m.reg_wptr,
+ priv->txd_fifo0.m.wptr & TN40_TXF_WPTR_WR_PTR);
+ }
+ if (unlikely(netif_queue_stopped(priv->ndev) &&
+ netif_carrier_ok(priv->ndev) &&
+ (priv->tx_level >= TN40_MAX_TX_LEVEL / 2))) {
+ netdev_dbg(priv->ndev, "TX Q WAKE level %d\n", priv->tx_level);
+ netif_wake_queue(priv->ndev);
+ }
+ netif_tx_unlock(priv->ndev);
+}
+
static void tn40_tx_free_skbs(struct tn40_priv *priv)
{
struct tn40_txdb *db = &priv->txdb;
@@ -713,6 +1106,10 @@ static irqreturn_t tn40_isr_napi(int irq, void *dev)
tn40_isr_extra(priv, isr);
if (isr & (TN40_IR_RX_DESC_0 | TN40_IR_TX_FREE_0 | TN40_IR_TMR1)) {
+ if (likely(napi_schedule_prep(&priv->napi))) {
+ __napi_schedule(&priv->napi);
+ return IRQ_HANDLED;
+ }
/* We get here if an interrupt has slept into the
* small time window between these lines in
* tn40_poll: tn40_enable_interrupts(priv); return 0;
@@ -730,6 +1127,25 @@ static irqreturn_t tn40_isr_napi(int irq, void *dev)
return IRQ_HANDLED;
}
+static int tn40_poll(struct napi_struct *napi, int budget)
+{
+ struct tn40_priv *priv = container_of(napi, struct tn40_priv, napi);
+ int work_done;
+
+ tn40_tx_cleanup(priv);
+
+ if (!budget)
+ return 0;
+
+ work_done = tn40_rx_receive(priv, budget);
+ if (work_done == budget)
+ return budget;
+
+ if (napi_complete_done(napi, work_done))
+ tn40_enable_interrupts(priv);
+ return work_done;
+}
+
static int tn40_fw_load(struct tn40_priv *priv)
{
const struct firmware *fw = NULL;
@@ -812,6 +1228,8 @@ static void tn40_hw_start(struct tn40_priv *priv)
tn40_write_reg(priv, TN40_REG_TX_FULLNESS, 0);
tn40_write_reg(priv, TN40_REG_VGLB, 0);
+ tn40_write_reg(priv, TN40_REG_MAX_FRAME_A,
+ priv->rxf_fifo0.m.pktsz & TN40_MAX_FRAME_AB_VAL);
tn40_write_reg(priv, TN40_REG_RDINTCM0, priv->rdintcm);
tn40_write_reg(priv, TN40_REG_RDINTCM2, 0);
@@ -913,15 +1331,30 @@ static int tn40_start(struct tn40_priv *priv)
return ret;
}
+ ret = tn40_create_rx_ring(priv);
+ if (ret) {
+ netdev_err(priv->ndev, "failed to rx init %d\n", ret);
+ goto err_tx_ring;
+ }
+
+ tn40_rx_alloc_buffers(priv);
+ if (tn40_rxdb_available(priv->rxdb0) != 1) {
+ ret = -ENOMEM;
+ netdev_err(priv->ndev, "failed to allocate rx buffers\n");
+ goto err_rx_ring;
+ }
+
ret = request_irq(priv->pdev->irq, &tn40_isr_napi, IRQF_SHARED,
priv->ndev->name, priv->ndev);
if (ret) {
netdev_err(priv->ndev, "failed to request irq %d\n", ret);
- goto err_tx_ring;
+ goto err_rx_ring;
}
tn40_hw_start(priv);
return 0;
+err_rx_ring:
+ tn40_destroy_rx_ring(priv);
err_tx_ring:
tn40_destroy_tx_ring(priv);
return ret;
@@ -933,12 +1366,15 @@ static void tn40_stop(struct tn40_priv *priv)
free_irq(priv->pdev->irq, priv->ndev);
tn40_sw_reset(priv);
tn40_destroy_tx_ring(priv);
+ tn40_destroy_rx_ring(priv);
}
static int tn40_close(struct net_device *ndev)
{
struct tn40_priv *priv = netdev_priv(ndev);
+ napi_disable(&priv->napi);
+ netif_napi_del(&priv->napi);
tn40_stop(priv);
return 0;
}
@@ -954,6 +1390,8 @@ static int tn40_open(struct net_device *dev)
netdev_err(dev, "failed to start %d\n", ret);
return ret;
}
+ napi_enable(&priv->napi);
+ netif_start_queue(priv->ndev);
return 0;
}
@@ -1203,6 +1641,7 @@ static int tn40_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
priv = netdev_priv(ndev);
pci_set_drvdata(pdev, priv);
+ netif_napi_add(ndev, &priv->napi, tn40_poll);
priv->regs = regs;
priv->pdev = pdev;
@@ -60,6 +60,25 @@ struct tn40_txd_fifo {
struct tn40_fifo m; /* The minimal set of variables used by all fifos */
};
+struct tn40_rxf_fifo {
+ struct tn40_fifo m; /* The minimal set of variables used by all fifos */
+};
+
+struct tn40_rxd_fifo {
+ struct tn40_fifo m; /* The minimal set of variables used by all fifos */
+};
+
+struct tn40_rx_map {
+ struct page *page;
+};
+
+struct tn40_rxdb {
+ unsigned int *stack;
+ struct tn40_rx_map *elems;
+ unsigned int nelem;
+ unsigned int top;
+};
+
union tn40_tx_dma_addr {
dma_addr_t dma;
struct sk_buff *skb;
@@ -87,6 +106,13 @@ struct tn40_priv {
struct net_device *ndev;
struct pci_dev *pdev;
+ struct napi_struct napi;
+ /* RX FIFOs: 1 for data (full) descs, and 2 for free descs */
+ struct tn40_rxd_fifo rxd_fifo0;
+ struct tn40_rxf_fifo rxf_fifo0;
+ struct tn40_rxdb *rxdb0; /* Rx dbs to store skb pointers */
+ struct page_pool *page_pool;
+
/* Tx FIFOs: 1 for data desc, 1 for empty (acks) desc */
struct tn40_txd_fifo txd_fifo0;
struct tn40_txf_fifo txf_fifo0;
@@ -115,6 +141,32 @@ struct tn40_priv {
char *b0_va; /* Virtual address of buffer */
};
+/* RX FREE descriptor - 64bit */
+struct tn40_rxf_desc {
+ __le32 info; /* Buffer Count + Info - described below */
+ __le32 va_lo; /* VAdr[31:0] */
+ __le32 va_hi; /* VAdr[63:32] */
+ __le32 pa_lo; /* PAdr[31:0] */
+ __le32 pa_hi; /* PAdr[63:32] */
+ __le32 len; /* Buffer Length */
+};
+
+#define TN40_GET_RXD_BC(x) FIELD_GET(GENMASK(4, 0), (x))
+#define TN40_GET_RXD_ERR(x) FIELD_GET(GENMASK(26, 21), (x))
+#define TN40_GET_RXD_PKT_ID(x) FIELD_GET(GENMASK(30, 28), (x))
+#define TN40_GET_RXD_VTAG(x) FIELD_GET(BIT(31), (x))
+#define TN40_GET_RXD_VLAN_TCI(x) FIELD_GET(GENMASK(15, 0), (x))
+
+struct tn40_rxd_desc {
+ __le32 rxd_val1;
+ __le16 len;
+ __le16 rxd_vlan;
+ __le32 va_lo;
+ __le32 va_hi;
+ __le32 rss_lo;
+ __le32 rss_hash;
+};
+
#define TN40_MAX_PBL (19)
/* PBL describes each virtual buffer to be transmitted from the host. */
struct tn40_pbl {