[netdrvr e100] experiment with doing RX in a similar manner to eepro100

I was going to say that eepro100's speedo_rx_link() does the same DMA
abuse as e100, but then I noticed one little detail: eepro100 sets  both
EL (end of list) and S (suspend) bits in the RFD as it chains it  to the
RFD list.  e100 was only setting the EL bit.  Hmmm, that's  interesting.
That means that if HW reads a RFD with the S-bit set,  it'll process
that RFD and then suspend the receive unit.  The  receive unit will
resume when SW clears the S-bit.  There is no need  for SW to restart
the receive unit.  Which means a lot of the receive  unit state tracking
code in the driver goes away.

So here's a patch against 2.6.14.  (Sorry for inlining it; the mailer
I'm using now will mess with the word wrap).  I can't test this on
XScale (unless someone has an e100 module for Gumstix :) .  It should
be doing exactly what eepro100 does with RFDs.  I don't believe this
change will introduce a performance hit because the S-bit and EL-bit  go
hand-in-hand meaning if we're going to suspend because of the S- bit,
we're on the last resource anyway, so we'll have to wait for SW  to
replenish.
(cherry picked from 29e79da9495261119e3b2e4e7c72507348e75976 commit)

1 files changed, 9 insertions, 63 deletions

diff --git a/drivers/net/e100.c b/drivers/net/e100.c
index 4d0e0aea72bf..71c6d334bd7f 100644
--- a/drivers/net/e100.c
+++ b/drivers/net/e100.c
@@ -282,12 +282,6 @@ enum scb_status {
         rus_mask         = 0x3C,
 };
 
-enum ru_state  {
-        RU_SUSPENDED = 0,
-        RU_RUNNING       = 1,
-        RU_UNINITIALIZED = -1,
-};
-
 enum scb_stat_ack {
         stat_ack_not_ours    = 0x00,
         stat_ack_sw_gen      = 0x04,
@@ -529,7 +523,6 @@ struct nic {
         struct rx *rx_to_use;
         struct rx *rx_to_clean;
         struct rfd blank_rfd;
-        enum ru_state ru_running;
 
         spinlock_t cb_lock                      ____cacheline_aligned;
         spinlock_t cmd_lock;
@@ -951,7 +944,7 @@ static void e100_get_defaults(struct nic *nic)
                 ((nic->mac >= mac_82558_D101_A4) ? cb_cid : cb_i));
 
         /* Template for a freshly allocated RFD */
-        nic->blank_rfd.command = cpu_to_le16(cb_el);
+        nic->blank_rfd.command = cpu_to_le16(cb_el & cb_s);
         nic->blank_rfd.rbd = 0xFFFFFFFF;
         nic->blank_rfd.size = cpu_to_le16(VLAN_ETH_FRAME_LEN);
 
@@ -1746,19 +1739,11 @@ static int e100_alloc_cbs(struct nic *nic)
         return 0;
 }
 
-static inline void e100_start_receiver(struct nic *nic, struct rx *rx)
+static inline void e100_start_receiver(struct nic *nic)
 {
-        if(!nic->rxs) return;
-        if(RU_SUSPENDED != nic->ru_running) return;
-
-        /* handle init time starts */
-        if(!rx) rx = nic->rxs;
-
-        /* (Re)start RU if suspended or idle and RFA is non-NULL */
-        if(rx->skb) {
-                e100_exec_cmd(nic, ruc_start, rx->dma_addr);
-                nic->ru_running = RU_RUNNING;
-        }
+        /* Start if RFA is non-NULL */
+        if(nic->rx_to_clean->skb)
+                e100_exec_cmd(nic, ruc_start, nic->rx_to_clean->dma_addr);
 }
 
 #define RFD_BUF_LEN (sizeof(struct rfd) + VLAN_ETH_FRAME_LEN)
@@ -1787,7 +1772,7 @@ static int e100_rx_alloc_skb(struct nic *nic, struct rx *rx)
                 put_unaligned(cpu_to_le32(rx->dma_addr),
                         (u32 *)&prev_rfd->link);
                 wmb();
-                prev_rfd->command &= ~cpu_to_le16(cb_el);
+                prev_rfd->command &= ~cpu_to_le16(cb_el & cb_s);
                 pci_dma_sync_single_for_device(nic->pdev, rx->prev->dma_addr,
                         sizeof(struct rfd), PCI_DMA_TODEVICE);
         }
@@ -1825,10 +1810,6 @@ static int e100_rx_indicate(struct nic *nic, struct rx *rx,
         pci_unmap_single(nic->pdev, rx->dma_addr,
                 RFD_BUF_LEN, PCI_DMA_FROMDEVICE);
 
-        /* this allows for a fast restart without re-enabling interrupts */
-        if(le16_to_cpu(rfd->command) & cb_el)
-                nic->ru_running = RU_SUSPENDED;
-
         /* Pull off the RFD and put the actual data (minus eth hdr) */
         skb_reserve(skb, sizeof(struct rfd));
         skb_put(skb, actual_size);
@@ -1859,45 +1840,18 @@ static void e100_rx_clean(struct nic *nic, unsigned int *work_done,
         unsigned int work_to_do)
 {
         struct rx *rx;
-        int restart_required = 0;
-        struct rx *rx_to_start = NULL;
-
-        /* are we already rnr? then pay attention!!! this ensures that
-         * the state machine progression never allows a start with a
-         * partially cleaned list, avoiding a race between hardware
-         * and rx_to_clean when in NAPI mode */
-        if(RU_SUSPENDED == nic->ru_running)
-                restart_required = 1;
 
         /* Indicate newly arrived packets */
         for(rx = nic->rx_to_clean; rx->skb; rx = nic->rx_to_clean = rx->next) {
-                int err = e100_rx_indicate(nic, rx, work_done, work_to_do);
-                if(-EAGAIN == err) {
-                        /* hit quota so have more work to do, restart once
-                         * cleanup is complete */
-                        restart_required = 0;
-                        break;
-                } else if(-ENODATA == err)
+                if(e100_rx_indicate(nic, rx, work_done, work_to_do))
                         break; /* No more to clean */
         }
 
-        /* save our starting point as the place we'll restart the receiver */
-        if(restart_required)
-                rx_to_start = nic->rx_to_clean;
-
         /* Alloc new skbs to refill list */
         for(rx = nic->rx_to_use; !rx->skb; rx = nic->rx_to_use = rx->next) {
                 if(unlikely(e100_rx_alloc_skb(nic, rx)))
                         break; /* Better luck next time (see watchdog) */
         }
-
-        if(restart_required) {
-                // ack the rnr?
-                writeb(stat_ack_rnr, &nic->csr->scb.stat_ack);
-                e100_start_receiver(nic, rx_to_start);
-                if(work_done)
-                        (*work_done)++;
-        }
 }
 
 static void e100_rx_clean_list(struct nic *nic)
@@ -1905,8 +1859,6 @@ static void e100_rx_clean_list(struct nic *nic)
         struct rx *rx;
         unsigned int i, count = nic->params.rfds.count;
 
-        nic->ru_running = RU_UNINITIALIZED;
-
         if(nic->rxs) {
                 for(rx = nic->rxs, i = 0; i < count; rx++, i++) {
                         if(rx->skb) {
@@ -1928,7 +1880,6 @@ static int e100_rx_alloc_list(struct nic *nic)
         unsigned int i, count = nic->params.rfds.count;
 
         nic->rx_to_use = nic->rx_to_clean = NULL;
-        nic->ru_running = RU_UNINITIALIZED;
 
         if(!(nic->rxs = kcalloc(count, sizeof(struct rx), GFP_ATOMIC)))
                 return -ENOMEM;
@@ -1943,7 +1894,6 @@ static int e100_rx_alloc_list(struct nic *nic)
         }
 
         nic->rx_to_use = nic->rx_to_clean = nic->rxs;
-        nic->ru_running = RU_SUSPENDED;
 
         return 0;
 }
@@ -1963,10 +1913,6 @@ static irqreturn_t e100_intr(int irq, void *dev_id)
         /* Ack interrupt(s) */
         writeb(stat_ack, &nic->csr->scb.stat_ack);
 
-        /* We hit Receive No Resource (RNR); restart RU after cleaning */
-        if(stat_ack & stat_ack_rnr)
-                nic->ru_running = RU_SUSPENDED;
-
         if(likely(netif_rx_schedule_prep(netdev))) {
                 e100_disable_irq(nic);
                 __netif_rx_schedule(netdev);
@@ -2058,7 +2004,7 @@ static int e100_up(struct nic *nic)
         if((err = e100_hw_init(nic)))
                 goto err_clean_cbs;
         e100_set_multicast_list(nic->netdev);
-        e100_start_receiver(nic, NULL);
+        e100_start_receiver(nic);
         mod_timer(&nic->watchdog, jiffies);
         if((err = request_irq(nic->pdev->irq, e100_intr, IRQF_SHARED,
                 nic->netdev->name, nic->netdev)))
@@ -2139,7 +2085,7 @@ static int e100_loopback_test(struct nic *nic, enum loopback loopback_mode)
                 mdio_write(nic->netdev, nic->mii.phy_id, MII_BMCR,
                         BMCR_LOOPBACK);
 
-        e100_start_receiver(nic, NULL);
+        e100_start_receiver(nic);
 
         if(!(skb = netdev_alloc_skb(nic->netdev, ETH_DATA_LEN))) {
                 err = -ENOMEM;